United States Patent (19) 11) 4,053,845 Gould 45) Oct. 11, 1977
(54) OPTICALLY PUMPED LASER AMPLIFIERS Levgyel, "Evolution of Masers and Lasers', Amer. Jour. of Physics, vol. 34, No. 10, 10/66, pp. 903-913. 76 Inventor: Gordon Gould, 329 E. 82 St., New York, N.Y. 10028 Primary Examiner-Nelson Moskowitz Attorney, Agent, or Firm-Lerner, David, Littenberg & (21) Appl. No.: 498,065 Samuel 22 Filed: Aug. 16, 1974 (57) ABSTRACT Optically pumped laser amplifiers are disclosed. One Related U.S. Application Data type of such amplifier utilizes an excitable medium, the 60 Continuation of Ser. No. 644,035, March 6, 1967, atoms, ions or molecules of said medium having well abandoned, and Ser. No. 804,540, April 6, 1959, defined energy states including a lowest state, a lower abandoned, said Ser. No. 644,035, is a division of Ser. state above said lowest state, and a higher state above No. 804,540, , and a continuation-in-part of Ser. No. said lower state, and a bright pumping light source 804,539, April 6, 1959. composed of a radiative substance different from such medium which radiative substance emits energy in a 51) Int. Cl? ...... H01S 3/091; H01S 3/22 spectral range which can be absorbed by such medium, 52 U.S. C...... 330/4.3; 331/94.5 G; and wherein the major portion of the energy absorbed 331/94.5 P by such medium causes transitions of the atoms, ions, or 58) Field of Search ...... 330/4.3; 331/94.5 G, molecules thereof to populate the higher state. Another 331/94.5 P, 94.5 D; 324/15F type of such amplifier utilizes a medium of atoms, ions, (56) References Cited or molecules, some of which have broad bands of en ergy levels corresponding to a broadband of absorption U.S. PATENT DOCUMENTS transitions and energy levels corresponding to at least 2,929,922 3/1960 Schawlow et al...... 330/4.3 one fluorescent emission transition, the upper energy levels of said broad bands being above the upper level FOREIGN PATENT DOCUMENTS of said fluorescent emission transition, and wherein 148,441 1959 U.S.S.R...... 330/4.3 some of the upper energy levels above the upper level 123,209 1959 U.S.S.R...... 330/4.3 of said fluorescent emission transition are rapidly quenched via non-radiating transitions to the upper OTHER PUBLICATIONS level of said fluorescent emission transition. In a pre Fabrickart, "Electronic and Ionic Devices (Transla ferred embodiment of the latter amplifier, the lower tion)', Trudy, vol. 41, 1940, pp. 236-296. energy level corresponding to the fluorescent emission Butaeva et al., "Investigations in Experimental and transition is relaxed by non-radiating transitions. Theoretical Physics', 1959, pp. 62-70, Studies in Exper imental and Theoretical Physics. 12 Claims, 7 Drawing Figures
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4,053,845 2 sion has a spectral distribution similar to that of the OPTICALLY PUMPED LASER AMPLIFTERS inducing radiation and may be in a very "sharp' line. This application is a continuation of both of my appli Spontaneously emitted photons, because of the ran cations, Ser. No. 644,035 filed on Mar. 6, 1967 and Ser. dom nature of the zero-point fluctuations, have no defi No. 804,540 filed on Apr. 6, 1959, which were co-pend- 5 nite phase or polarization. Because the zero-point fluc ing herewith and both are now abandoned. My continu tuations contain all frequencies, spontaneously emitted ation application Ser. No. 644,035 was co-pending with radiation has a finite bandwidth, characterized, at the and (1) a divisional application of my application Ser. least, by a Lorentzian line shape. No. 804,540 filed on Apr. 6, 1959, now abandoned, and In thermal equilibrium, the populations of two states (2) a continuation-in-part of my application Ser. No. O are related by the Boltzmann distribution factor: 804,539 filed Apr. 6, 1959, now abandoned. The present invention relates to amplifiers, and par ticularly to optically pumped light amplifiers. Ehigh - Etow A short explanation of the physical principles in KT volved will be helpful in explaining the nature of the 15 invention. It is known that atoms, ions or molecules (hereinafter Thus, in equilibrium the population of a higher energy called molecules) ordinarily exist in so-called "station state is less than that of a lower energy state. In particu ary' states possessing a more or less well defined en lar, the population of a state separated from the lowest ergy. While in such a state a molecule does not exhibit by an optical frequency is practically nil at ordinary an oscillating electric or magnetic moment. However, temperatures. Induced transitions under these condi since a molecule is made up of charged particles, it will tions necessarily absorb photons from the radiation be perturbed by any oscillating electric or magnetic field. field in which it may lie. When so perturbed, a molecule The foregoing principles can be utilized to devise originally known to be definitely in stationary state "a" 25 apparatus for microwave amplification by stimulated will possess a certain probability of being found in state emission of radiation which has been termed a MASER. “b' with different energy. When in such a "mixed' If by some means the population of a higher energy state, the molecule may exhibit an oscillating electric or state is made larger than that of a lower energy state, magnetic moment (i.e., it may appear as a system of 30 induced transitions must necessarily result in the emis oscillating charges, or charges in changing orbits). A sion of photons to the radiation field. Thus a molecule molecule will undergo a transition from state 'a' to may emit spontaneously a photon which in turn may state 'b' (i.e., have a large probability of being in state induce coherent emissions in neighboring molecules, "b') if the induced electric or magnetic moment oscil adding to the total radiation energy. If the transition is lates with almost the same frequency as the applied is at a microwave frequency, the system may be enclosed electric or magnetic field, and if the polarizations and in a cavity resonant at the same frequency and the es phases of the oscillations correspond. The frequency of cape of the photons prevented. If the power loss from the oscillating moment is determined by the Einstein the cavity is less than the power emitted from the mole relationship: cules, the system will oscillate with a frequency which fluctuates much less than the (Lorentz) bandwidth of the transition. The condition for MASER oscillation in where a gas is that the excess population density vo E the oscillation frequency h = Planok's constant h N - Na >> - - - AE = the energy difference between the two molecu 45 8ar pro lar states. The same equation E = hly gives the energy of the if the gas fills the cavity, photons associated with the electro-magnetic field. The T = T = T, is the relaxation time or state lifetime. photon density is proportional to the energy density of Q = the "quality factor' of the cavity. the field. During a transition, a photon or "quantum' 50 p is the oscillating electric or magnetic moment char electro-magnetic energy is emitted to or absorbed from acterizing the transition. the field, depending on whether the molecule is chang If the condition for oscillation is not quite met but ing from a higher to lower energy state or vice-versa. external power is coupled into the cavity, the "sensi Even when there is no radiation energy density of the tized' or "pumped' molecules will add to or amplify right frequency directly observable at the molecule, 55 the signal. Because power is lost through the output spontaneous transitions occur from higher to lower coupling, the condition for infinite gain, at optimum states with the emission of photons. These transitions output, is are actually induced by random fluctuations in the elec tro-magnetic field of so-called "empty' space. The photons emitted during an induced transition N - N --rpr unloaded have the same phase and polarization as the inducing wave - i.e., they are "coherent' with it. A single atom This amplification adds very little random "noise' to may radiate a photon in any direction. However many the amplified signal. The minimum noise is determined atoms distributed over a finite volume and radiating by thermal fluctuations in the radiation field or by ran coherently cooperate to generate a wave having the 65 dom spontaneous emission, whichever is larger. same propagation vector as the inducing wave, within Several methods have been proposed for maintaining the limits of a diffraction pattern. That is, they amplify an excess population in the higher of two molecular the inducing wave. The radiation from induced emis energy states of a gas filling a resonant MASER cavity.
4,053,845 3 4. One form of MASER which has been proposed Apparatus according to the present invention pro achieves "optical pumping" by unpolarized light. vides the capability of amplifying light coherently, at The discussion of this form of "optical pumping' will least with respect to frequency and phase and in some be given in terms of rubidium (atoms) but would be cases also with respect to direction of propagation, and similar for other cases. Light, characteristic of various axis of polarization. Insofar as is known no apparatus spontaneous transitions in Rb, is generated in a dis with this capability has heretofore been produced. charge lamp and passed through a filter. The filter re A coherent infrared light molecular amplifier and moves all frequencies except that component line which generator has been proposed in U.S. Pat. No. 2,851,652 induces transitions from the F = 1 hyperfine level of to Robert H. Dicke. This apparatus and methods pro the ground electronic level to some particular higher 10 posed by Dicke differ in many respects from those of electronic level. Spontaneous decays back to both hy the present invention. In the Dicke device ammonia perfine ground levels will result in a net pumping of Rb molecules are provided in a bounded volume wherein atoms from F = 1 to F = 2. the higher of two molecular energy states is more To maintain an excess population in F = 2 over F = highly populated than the lower; this is accomplished 1, the optical pumping rate need only exceed the colli 15 by physically separating, by electric fields, the mole sion relaxation rate which may be made as small as cules in the lower state from a beam of molecules before 10/sec. Of course this minimum pumping rate would give a correspondingly small power output from the the beam is permitted to enter the bounded volume. MASER. Such activated molecules are capable of amplifying an 20 electromagnetic wave within a particular frequency In the light amplifier, on the other hand, the negligi range. ble thermal population of higher electronic states and the high rate of spontaneous emission from these states, The present invention, on the other hand, causes the make necessary a much higher pumping rate. In gen atoms, ions or molecules of the working medium to be eral, these effects preclude light amplifier operation activated to produce the desired population excess in 25 the higher energy level without actual physical separa between a higher state and a ground state. Usually, a tion. Furthermore, the desired population excess is pro transition between two higher electronic states must be duced within the bounded volume in which emission utilized. takes place in the present invention; whereas, in the Like the MASER, the light amplifier will operate on Dicke apparatus the physical separation to produce the the principle of induced transitions from a higher en ergy state to a lower energy state with smaller popula 30 desired population distribution is accomplished outside tion. However, the techniques usable and possible are the cavity after which the working medium is physi appropriate to the optical region of the electro-mag cally transported into the bounded volume in which netic spectrum. This frequency range is defined for the stimulated emission takes place, present purpose by the limit of transparency of materi A simple very effective apparatus results from the als in the infrared and ultraviolet to be approximately: 35 different method and apparatus for activation utilized in 10 cmd. As 10 cm the present invention. 3 x 101 cycles/sec 4,053,845 7 8 ergy level to the lower energy level with the emission Considerable study has been made of the phenome of more light of this same frequency. non of "sensitized fluorescence'. Atoms of one kind, Accordingly, when the pumping rate due to excita excited to a particular electronic level, may, on collision tion from the source 24 is sufficiently great to maintain with atoms of a second kind, transfer their excitation a large population difference between these two levels energy. It has been shown experimentally and theoreti in favor of the higher level, and when losses in the cally that the transfer process is most probable if two cavity are reduced to a sufficiently low level as by conditions are fulfilled: maximizing the reflectivity of the surface 20, conditions a. The smaller the energy difference between the for sustained oscillation will be met and the apparatus of levels of interest in the two kinds of atoms, the greater FIG. 2 will operate as a nonresonant light oscillator. 10 is the collision cross-section for the exchange. Obviously, if the conditions for oscillations are ap b. The total electronic angular momentum of the two proached but are not met, light of the appropriate fre atoms remains the same before and after the collision quency (8660 Angstroms) introduced into the cavity (Wigner partial selection rule). will be amplified by the stimulated emission of radia In connection with rule (a), the energy difference tions and the output of the cavity at that frequency will 15 must be converted to or from kinetic energy of the be greater than the input thus providing amplification, atoms. If the energy difference is less than "thermal but self-sustained oscillation will not occur. energy' ( 4,053,845 11 12 circuit over a plurality of circuits of the reflecting ting, the emitted radiation will also be a substantially means is not the same for each and every portion of the plane wave with the same propagation vector except reflecting surface within the accuracy of a fraction of for small diffraction effects. With this understanding it the wavelength, interference will be produced and a will be seen that the resonant light amplifier of FIG. 3, resonant nature of the system will be diminished or although it has only small reflecting surfaces compared destroyed. with its total cavity internal area, effectively confines It is likely that one limit of the efficiency of the system the amplifying operation due to the fact that only light will be the tolerances to which flat optical surfaces may energy within a very narrow range of frequency and be produced. It may be impossible to obtain a surface propagation direction is amplified and this energy has a with a closer tolerance of flatness than approximately 10 one-fiftieth of a wavelength as a practical matter. This, direction of propagation vector such that it is substan of course, will limit the efficiency of resonant light tially contained between the two reflecting surfaces. amplifiers utilizing prisms as well as the resonant light There will be slight losses of energy off the edge of amplifier utilizing flat mirrors. In the case of the mir the reflectors due to slight discrepancies in the angle of rors, however, it would also be necessary to place and 15 propagation of the rays being amplified. This slight retain the mirrors in respective ends of the cavity energy loss will not be sufficient in a well designed (which may be separated in a typical case by 30 centi apparatus to prevent proper operation of the device. meters) in parallel relationship with a tolerance of one Within its frequency and angular limits, determined fiftieth of a wavelength, approximately. This can likely by the dimensions and loss coefficient on reflection, the be achieved although it would necessarily involve a 20 resonant light amplifier will amplify plane waves con phenomenal degree of precision and expensive tech tinuously variable in direction and frequency. niques that would go with such a precise operation. If the input wave is plane, the output wave is almost Furthermore, the completed device would be highly but not exactly plane. The finite size of a wavelength, A, sensitive to disturbances and vibration of all types in allows the wave front to spread as it travels. At great cluding physical accelerations, changes in temperature, 25 distances from a circular end-plate, the wave front, etc. instead of remaining a circle of constant diameter, ex The prisms 69 and 71 are preferably provided with hibits the Fraunhofer diffraction pattern of intensities. non-reflective coating on their front faces 74 and 75, as In this pattern approximately 98% of the light falls in a light reflected from these faces will generally be lost central spot of angular radius due to being out of phase or slightly misdirected and 30 will not add coherently to the main standing wave in A8 = 1.220(A/2R) the cavity. w The faces 73 of the prism 71 would normally be sub more than half the light falls in a cone of half this angu stantially 100% reflective. An output from the cavity lar radius. If the wave is focused on a nearby plane, one (or in the case of an amplifier operation, an input as 35 observes the same pattern instead of a point. The Ray well) may be provided through one or both of the faces leigh criterion for angular resolution of two plane 72 of the prism 69. The face 72 may be rendered par waves focused in a telescope is that the waves shall tially transmissive by placing on or near the face a mate make an angle with each other equal to A6. That is, the rial which has an index of refraction which does not maximum of one falls on the first dark ring of the other differ from the index of refraction of the prism suffi pattern. Thus plane waves from different points of a ciently to provide total internal reflection. By this distant object could be amplified coherently by the means, any desired portion of the light impinging on resonant light amplifier and then focused on a screen or one or both faces 72 may be transmitted to the outside the face of a television camera tube. The resulting image of the cavity. Conversely, if the apparatus is to be used could be scanned or otherwise used. as an amplifier, thus necessitating an input, the same 45 path or a similar path may be used for the input to the If a plane wave passes through a circular aperture, light amplifier. then at nearby distances the wave starts to spread and In the case of an amplification operation as contrasted forms the Fresnel diffraction pattern. to an oscillator operation, there will generally be a loss Thus as a "plane' wave reflects back and forth inside of energy involved in transmitting the input signal into 50 the tube, light dribbles out of the cylindrical space be the cavity and transmitting the output signal out of the tween the reflectors. The fraction of light lost by this cavity. Obviously any normal type of transmission path mechanism in travelling a distance l = L/a is very for light energy into the cavity will also provide a path approximately given by for the same kind of light energy out of the cavity. One may expect a loss on the order of 50% in this operation, 55 but this will not be serious in view of the overall gain dbp = fract. lost st -- L produced by the light amplifier. Such a problem need 2a not arise in the case of a light oscillator as no input signal is required due to the fact that oscillations are where L/a is the mean distance travelled by a photon built up from ever-present random fluctuations as is the before it is lost at a reflector. case with other types of oscillator devices. If db->1 then the effective loss on reflection, a, will be appreciably increased. This puts a lower limit on the OPERATION OF RESONANT LIGHT radius of the reflector. If AMPLIFIER L = 100 cm As previously explained, the induced emission from 65 A = 5 X 10-5cm atoms is coherent with the inducing radiation. That is, it a = 0.05 has the same phase, frequency and polarization. If many 2R = 1 cm atoms over the breadth of the inducing wave are emit then dpi si 0.3 which is about as high as desirable. 4,053,845 13 14 MIRRORTYPE RESONANT LIGHT AMPLIFIER or the rate of energy loss is FIG. 4 shows an alternative form of resonant light amplifier device comprising a cavity 101 having trans - dE.-- parent side walls and enclosed at its ends by flat mirrors at 102 and 103. The interior 104 of the cavity 101 is filled with a As a increases, the gain of the light amplifier will de sensitized working medium such as sodium vapor. cline proportionately in the range of linear amplifica Placed around the cavity 101 is a concentric cylindrical tion. A practical measure of the limiting angle at which discharge tube 105. The surface 106 may be provided 10 effective amplification obtains might be that angle for with a reflective coating to conserve light while the which inner wall 107 of the discharge tube 105 is transparent to the desired component of the light produced in the 2cabsorption. discharge tube. Electrodes 108 are provided in the discharge tube 105 15 e abs. which are supplied with power from a power supply 2R L 109 through leads 111. O In the form of apparatus shown in FIG. 4 the medium in the gas discharge tube 105 is a mixture of sodium and e = 2yr mercury. As previously explained, such a mixture pro 20 vides an enhancement of a desired spectral line by colli the maximum one might conceive would be 6 - 0.1 sions of the second kind. This brings about a considera radian, while for the dimensions immediately above, bly increased intensity of the desired spectral line in the lamp and increases the optical pumping power which 8at 5 x 10' radian. creates the desired population distribution in the energy 25 levels of the atoms of sodium in the interior 04 in the The fact that the loss coefficient falls off with increasing cavity 101 conducive to stimulated emission of light angle, 6, determines a most important characteristic of radiation. the resonant light oscillator output, a very narrow In FIG. 4 the reservoirs, ovens, and auxiliary equip beam. ment for maintaining the proper atmosphere in the dis 30 It can be calculated that virtually the entire output charge tube 105 and in the cavity 101 have been omitted beam will fall within the Fraunhofer diffraction pattern for simplicity. Such elements may be provided for the for 6 = 0. It may also be shown that, with P = 1 watt apparatus of FIG. 4 in accordance with other figures of at M = 1, the frequency bandwidth of the output beam the drawings or any other suitable means for maintain 35 will be less than 100 cycles/sec. This is residual band ing the appropriate atmosphere may be utilized. width due to the noise discussed below. The mirrors 102 and 103 may be metallized or multi layered interference reflectors. The latter are almost As pointed out previously, the random-fluctuation lossless (i.e., the transmission plus the reflection equals spontaneous emission background in the visible will approximately 100%). Interference reflectors may have correspond to transitions induced by thermal radiation a very high reflectance, for a given wavelength, de at a temperature of 30,000 K. However, this is not so pending on the number of layers. A practical achieve high as it first appears, since a resonant light amplifier ment is 98% in the visible for a 7-layer reflector. Flats may discriminate against all signals outside a narrow with a closer tolerance than approximately 1/50 M are optical band and against all directions of propagation not currently available so if a resonant system is desired outside the central Fraunhofer lobe. and more accurate flats are not available, higher reflec 45 It can be estimated that the minimum equivalent noise tance would not be useful. An additional advantage of input power in a Fraunhofer lobe is given by : interference reflectors is that photons from other than the desired transition would not be reflected (due to Past 1.5 x 10 watts in the visible. frequency selectivity), and hence, undesired stimulated transitions would be prevented. 50 If the bandwidth, Af, is limited in a succeeding elec It is clear from FIG. 4 that a plane wave travelling in tronic amplifier, it can be shown that the following a direction other than 90 to the mirror surface will expression for this noise holds "walk' off the edge and loss energy at a rate faster than the normal wave. The lateral displacement per reflec tion is 55 P = h; Ava x = L sins.L6 The fraction of wave energy which walks off at each Thus the minimum noise depends on the square root of reflection is roughly the bandwidth but not on the area of the reflectors 102, 60 103 at the tube ends. Le The apparatus of FIG. 4 may be used as an amplifier as distinguished from a self-sustained oscillator by limit ing the "gain', that is, by limiting the amount of light So the effective loss coefficient on reflection is power introduced from the discharge tube 105 so that a 65 self-sustained oscillation is not produced. A signal may, therefore, be introduced through the mirror 103 as indi a = aTit. -- - 2R - cated by the arrow 112 as the mirrors 103 and 102 are partially transmitting. 5. it's . 4,053,845 15 16 The light ray indicated at 112 will cause stimulated However, in none of these cases is the overlap good emission of light energy within the cavity 101 which is enough for high excitation efficiency. On the other coherent with the input signal with respect to phase, hand numerous examples of the excitation of molecules frequency and direction of propagation. The amplifica by coincident atomic lines have been observed. tion within the cavity is rather selective with respect to Information is scarce on fluorescence of molecules direction of propagation and frequency so that only a containing more than two atoms. Therefore, only diato relatively small range exists with respect to these two mic molecules are considered herein. parameters within which an input wave will be ampli Each electronic level in a diatomic molecule is split fied in the device. into approximately 50 vibrational levels and each vibra The output from the light amplifier will be transmit 10 tion level into approximately 200 rotational levels. ted through mirrors 103 and 102 as indicated by the Therefore, we may expect more than 100,000 absorp arrows 113 and 115. Either or both of these outputs may tion transitions from populated levels in every molecule be utilized, depending upon the particular application on the average. As expected, there is generally at least or system in which the light amplifier is used. one coincidence of a bright atomic spectral line with As in the case of previously discussed light amplifier 15 some resonance transition of a given molecule. By the devices, the device of FIG. 4 may also be utilized as an same token the emission from a discharge in a molecular oscillator simply by increasing the efficiency of the gas is divided into many weak lines. These cannot be process or otherwise increasing the gain of the amplifier excited by an external lamp conveniently. to the point where self-sustained oscillations are pro Materials which transmit u.V. radiation below 2,000A duced. In certain applications it may be desirable to 20 are not available. Therefore, the light amplifier process utilize the same apparatus as both an oscillator and an previously described cannot be used, i.e., excitation to a amplifier, on a time sharing basis, for example. This may high electronic level with light amplifier emission to an be accomplished, for example, by periodically increas intermediate level whose population is kept low by ing the light energy produced by the discharge tube 105 rapid spontaneous decay to a ground level. Instead the to momentarily produce self-sustained oscillations. It 25 properties of molecules require and permit another should be understood that the optical system can be mechanism for keeping the lower level population replaced by other optical systems such as the one illus lower than some higher level population. This mecha trated in FIG. 3, and also that the exciting process uti nism is relaxation of the lower level population by colli lized in FIG. 4 may be replaced by other exciting pro sions of the second kind. cesses previously described. 30 To exemplify the whole process, the molecule I, is It should be noted that the apparatus of FIG. 4 does considered. (See FIG. 5). not differ greatly from the nonresonant cylindrical am The first member of the sodium principle series at plifier previously described, and the resonant apparatus 5893A (See FIG. 2) coincides with one of the numerous in FIG. 4 could be converted to a nonresonant amplifier 35 absorption lines of the iodine molecule. The transition by substitution of diffuse reflectors for the mirrors 102 in question is from a rotational sublevel of the y = 2 and 103. vibrational level of the ground electronic state (e'g') up EXCITATION BY COINCIDENT SPECTRAL to the J = 30, y = 17 sublevel of the (37th) state. The LINES y = 2 of (egt) levels are well populated in thermal equilibrium at room temperature (see lower right cor Previously, the excitation of atoms by resonance radi ner of FIG. 8), while y = 7 of (e'g+) has less than 1% of ation was discussed. The emitted spectral lines from a lamp of the same substance necessarily coincide with the population and y = 17 of (3rt) has none. frequencies absorbed most strongly by the same type A 1 cm thick layer of Ivapor at a few mm Hg pres atoms in the light amplifier. However, as pointed out in sure absorbs most of the Na light and raises 12 molecules the discussion of sodium excitation, the intensities of 45 to the upper level at a rate lines emitted from the lamp during decay of higher states are quite weak. It was also pointed out that the din Parait intensity of certain of these higher resonance lines could dt = --. be enhanced by collisions of the second kind with meta stable atoms. Another way of obtaining strong excita 50 In the absence of light amplifier action, the atoms decay tion to higher electronic levels is by accidentally coinci at a rate dent bright emission lines from another atom. The chance coincidence of two appropriate atomic din lines is small. There is room for some 300,000 spectral dt -- ". ye'ea(all other states) lines of Doppler width with only slight overlap 55 throughout the visible and near ultraviolet range. There where eA = spontaneous radiative decay rate are at most 1,000 useful resonance transitions in conve ty = rate of removal by relaxation collisions with nient atoms and approximately 30 bright atomic lines other Imolecules (quenching collisions). The cross-sec with which to excite them. Thus, there is about a 10% tion for these collisions is very high since many I2 states chance of one good coincidence. At least three moder are closely spaced in energy. About 5% of the mole ately close coincidences are known, as shown in Table cules decay to y 7 of (e'g+). Then, by the same III. method of decay as that first described herein, the dy TABLE III namic equilibrium rates of population change are "COINCIDENT' ATOMICSPECTRAL LINES 65 dini w- - Pavail dt - l n(y -- ea) 4,053,845 17 18 -continued in turn raises the required illumination intensity for an d externally excited resonant light amplifier: T-t = 0 = nA( – ) - nic and awailable AR 4hc CA - Pawaii laf(v) A n = a - The line shape factor, – y in A(h - ) 10 It is to be noted that atoms can be removed from y = 7 7tAv of (egt) only by relaxation collisions to other sublevels for a Lorentz line, and approximately the same for other of the ground electronic state. Then if the I pressure line shapes. Thus most condensed systems will require a (-5 mm Hg) is such that high power input to excite light amplifier action. 15 An additional difficulty is that excitations in solids or y at EA at 20XA(h - )at 10/sec liquids are usually "quenched' by non-radiative pro then CeSSS. n/nast 20 > 1, One should accordingly use substances which fluo resce (reradiate) with high quantum efficiency. Some which is necessary for light amplifier action. 20 substances which absorb the powerful Na(5893A) line The further analysis is quite similar to that for the and fluoresce efficiently are the merocyamine dyes, Na(6P-4S) light amplifier transition. The values in fluorescein, Meldola blue, and Rhodamine 'B'. More volved are not much different and so for a light ampli promising are certain substances in which the electrons fier tube 1 cm diameter X 100 cm long, the required 25 which take part in the excitation lie in the interior of the Na(5893A) intensity from a discharge lamp arranged as atoms or ions concerned and are shielded from environ a jacket is mental perturbations. Such substances, including the I2 10-3 watts/cm2 steradian. porphyrins, ruby, and rare earth ions have much nar As pointed out previously, the intensity in the first line rower lines. of the Na principle series can easily be made greater 30 The use of a polycrystalline solid entails the refraction than 0.1 watts/cm2 steradian, with a factor of 100 to and reflection of a light wave at the crystal interfaces, spare. preventing the lossless reflection of a wave back and From the above explanation it will be seen that al forth between light amplifier reflectors. To avoid this a though a light amplifier may be constructed utilizing single crystal ruby could be used. light energy from one substance to excite a different 35 The difficulties inherent in the use of solid or liquid substance having a coincident spectral line, the known working mediums may be minimized by use of, for combinations of monatomic substances bordering on example, the rare earth ion, Eut hit, in liquid solution. coincidence are not promising. The angular momentum sublevels of the first two elec On the other hand, the coincidences of an atomic line tronic states are shown in FIG. 6. with a resonance transition of a molecule often provides The J-sublevels are further split into states and one of a very high degree of coincidence suitable for use as an the components of the J' = O->J" = 1 transition over excitation process in a light amplifier according to the laps the Na 5893A line. The upper J-levels are rapidly present invention. quenched to the lowest two J-levels (y=2.5 X An example of such a coincidence usable as an excit 1012/sec) but transitions between the upper and lower ing process is the coincidence of the first member of the 45 electronic states occur only by radiative emission at the sodium principal series at A = 5893 Angstroms when slow "forbidden' rate, y at 103/sec, in the case of euro very nearly coincides with one of the absorption lines of pium sulfate in water. the iodine molecule. The ions may be excited by sodium radiation to J'=0 Construction of a light amplifier device utilizing this and decay to any of the J' levels. The two strongest type of excitation would be generally similar to that 50 fluorescent transitions at M = 81 10A and 6881A are previously described except that the excitation lamp suitable for a liquid filled light amplifier. would be a sodium discharge lamp while the working The J-quenching interaction gives rise to a line width medium within the cavity would be iodine vapor. Amat 5 x 1011 cycles per sec or ANs 6A. This line width is much sharper than those of other condensed fluores LIQUID OR SOLID WORKING SUBSTANCES 55 cent substances but broad compared to the spectral lines The "line' width AJ, of radiative transitions in ions, emitted by atoms in a low pressure discharge (AN atoms or molecules within liquids or solids is generally at 0.01A). Therefore, one may artificially increase the quite broad because of continuous strong interaction power of the Na discharge lamp to get the necessary with neighboring atoms. The uninterrupted phase life power without worrying about line distortion. time, The necessary intensity of illumination is given by the equation for I available above and is between 0.1 and 1.0 l watts/cm stere. A commercial "General Electric' lamp T tAv - 2 x 10 sec typically, with broadened and reversed sodium lines emits just about this intensity. while the spontaneous radiative decay time remains 65 Thus it appears that when for particular applications long: T ) 10-8 sec. a condensed working substance, such as a liquid is desir The effect of this is to raise the density of excited able, such a working substance may be utilized in a atoms, etc. required for light amplifier oscillation. This cavity such as shown in FIG. 3, one example of such a ... "Bits. 4,053,845 19 20 working substance being europium sulphate in water. nant light amplifier 421 may be on the order of 10-8 Excitation would be provided by a sodium discharge seconds, the shutter 425 may be constructed to have an lamp similar to commercially available types with a output having a rise time on the order of 10-11 seconds. broadened sodium line and emitting an intensity of be A shutter 425 comprises a mirror 426 which is very tween 0.1 and 1.0 watts per cm2 stere. rapidly rotated about an axis indicated at 427. An It will be appreciated that excitation by resonance opaque member 428 is provided having a narrow slit radiation, is generally applicable to both the nonreso 430. For the position of the mirror 426 shown in FIG. 7, nant and resonant type of light amplifier apparatus, as the rays 423 from the pulsed resonant light amplifier 421 are the various possible working medium discussed. are focused on the slit 430 and accordingly pass through 10 RESONANT LIGHT AMPLIFIER FOR the opaque member 428. As the mirror 426 is rotated, GENERATION OF TRANSIENT PULSES the rays from the amplifier 421 are swept across the opaque member 428 and periodically, for a very short For particular applications it may be desired to oper time interval, pass through the slit 430. ate resonant light amplifier apparatus to generate tran The width of the slit 430 is preferably that of the sient pulses of light energy. Such pulses will generally 15 width of the Fraunhofer pattern for the light beam at have the characteristics of the output of a resonant light that particular point. The width of the Fraunhofer pat oscillator, namely narrow frequency bandwidth, near tern will be greater as the distance of the opaque mem planarity of wave shape, etc. In addition, the transient ber 428 from the mirror 426 is increased. This distance pulses will have their energy concentrated in a very may be set at any convenient value and, if desired, the short time. This time period may be shorter than 10-8 20 seconds. The length of the pulse may, of course, be path of the light rays 423 may be folded by the use of longer and is subject to control, as is the shape of the mirrors or the like in order to make the shutter appara pulse to some extent, all as will later be explained. The tus of manageable size. For example, if the opaque intensity of the pulse will be considerably higher than member 428 is placed 10 meters away, the width of the light intensity obtained with comparable apparatus in 25 Fraunhofer pattern will be approximately 1/10th of 1 steady state operation. The light amplifiers of either the millimeter. The cutting of a slit of this width in the resonant or nonresonant type can, of course, be oper opaque material 428 presents no difficulties. ated in pulse fashion simply by pulsing the source of The mirror 426 is preferably rotated at a very high exciting energy such as the light excitation or the elec speed to obtain a pulse having a very short rise time trical discharge excitation. 30 from the shutter 425. If the velocity can be raised to 106 In the previously explained operation of light ampli radians per second, a pulse of approximately 10-11 sec fier devices, the stimulated emission added coherently onds can be obtained. Known techniques for obtaining to the inducing radiation. Except for the refraction high rotational velocity can be utilized in the construc effects, a wave-train traveling through an activated tion of the rapidly rotating mirror 426. For example, the light amplifier medium is linearly amplified as long as 35 mirror can comprise a ground "flat' on a small metal the density of excited atoms (or ions or molecules) re cylinder and can be placed in an evacuated enclosure mains substantially unchanged are provided the transi and provided with a substantially frictionless suspen tion is not "power broadened'. By means of operation sion. If desired, magnetic suspension can be utilized. outside the above limits, different effects are produced The mirror may be brought to a high rotational velocity (e.g., non-linear amplification), and apparatus utilizing by a rotating magnetic field. these effects has capabilities beyond those of the previ It will be understood that the particular shutter ar ously discussed light amplifier devices. rangement described with reference to FIG. 7 is a pre Apparatus for producing light pulses by the utiliza ferred form which is capable of attaining a very shor tion of light amplification in a light amplifier with non trise time for the output pulse from the shutter. The reflecting walls is shown in FIG. 16. A pulsed resonant 45 operation of the nonresonant non-reflecting light ampli light amplifier is indicated schematically at 421 and the fier of FIG. 16 is not limited to use with such extremely description thereof. high speed shutters. Thus, in many instances a slower The pulsed resonant light amplifier 421 is controlled and relatively simpler shutter such as a Kerr cell may be by a pulse generator and timing circuit 422 as previ used to provide a light pulse to the non-reflecting ampli ously explained. 50 fier tube. Furthermore, although a resonant light ampli The output from the pulsed resonant light amplifier fier provides a desirable type of light source for pulsing 421 is in the form of light pulses indicated by arrows the non-linear light amplifier tube, any other light 423. source of appropriate frequency could be utilized if These light pulses are directed as desired such as by controlled to give appropriate short duration light the lens 424. 55 pulses. In order to take maximum advantage of the amplifica The light on the shutter 425 is directed as by means of tion effect in a non-reflecting, nonresonant light ampli a lens 429 into a non-reflecting light amplifier tube 431. fier according to the present invention, it may be de The amplifier time 431 comprises a closure 432 having sired to provide the non-reflecting amplifier with a light an input window 433 and an output window 434. The pulse having as short a rise time as possible. Otherwise, interior 435 of the non-reflecting light amplifier tube is some of the energy stored in the non-reflecting ampli filled with a suitable working medium. When utilized in fier will be expended in amplification of the low inten conjunction with a pulsed resonant light amplifier 421, sity leading portion of the input pulse. the working medium of the non-reflecting light ampli Accordingly, a very high speed shutter arrangement fier tube 431 will generally be the same as that of the is illustrated in FIG. 7 for obtaining a pulse output hav 65 pulsed resonant light amplifier 421. In any case, the ing a very short rise time, e.g., a sharply rising intensity working medium of the amplifier tube 431 will be such with an intensity rise time of less than approximately that it is stimulated by the exciting light introduced 10-7 seconds. Whereas the rise time of the pulsed reso through the imput window 433. 4,053,845 21 22 The output from the non-reflecting light amplifier higher energy level at a given point before the entire tube 431 is projected out through the output window pulse wave-train passes this point in the light amplifier 434. tube. Under such conditions it will be apparent that The nonresonant non-reflecting light amplifier appa while the first portion of the input wave-train of light ratus of FIG. 7 operates as follows. will be amplified to a substantial extent, the trailing The operation of the pulsed resonant light amplifier portion of the wave-train will not be amplified or will 421 and of the shutter 425 have previously been ex be only slightly amplified. plained. It should be noted that the shutter 425 should As the pulse passes through the light amplifier tube be synchronized with the pulse of the pulsed reasonant 431, this effect will be highly cumulative for as the light amplifier 42 so that the open condition of the 10 intensity of the leading portion of the wave-train is built shutter 425 occurs as nearly as possible to the maximum up it will tend to more completely and more rapidly intensity of the light pulse from the pulsed resonant depopulate the upper energy level in the volume light amplifier 421. This function is accomplished by the through which it passes so that there will be effectively pulse generator and timing circuits 422. an exponential growth of the intensity of the leading Light pulses from the shutter 425 pass through the 15 portion of the pulse together with a generally corre lens 429 where they are collimated. The collimated sponding shortening of the pulse due to the lack of light pulse passes into the non-reflecting light amplifier amplification of the trailing portion of the pulse wave tube 431 through the input window 433. In FIG. 7 the train. excitation means for the non-reflecting light amplifier From the foregoing explanation, it will be seen that tube 431 is omitted for simplicity. It will be understood 20 the non-reflecting light amplifier tube 431 produces a that the working medium in the interior 435 of the am great intensification of the input pulse, together with a plifier tube 431 will be excited so that there is an excess considerable shortening of the pulse length. The short population of atoms, ions, or molecules in an upper one ening of the pulse length which can be obtained is lim of two energy levels separated by the frequency of the ited by the fact that the Fourier transform of a short stimulating light from the pulsed resonant light ampli 25 pulse contains frequency components far removed from fier 421. The activation energy for the working medium the nominal frequency. Thus, as the pulse becomes in the light amplifier tube 431 may be provided by light shorter and shorter, the energy in the pulse will cease to energy introduced through the wall 432, by an internal be concentrated at the nominal frequency; as a result the discharge, or by any other means such as those de efficiency of the process will deteriorate, thus limiting scribed hereinbefore. 30 the shortening of the pulse which can be obtained. Due It will be noted that reflection means are not included to this effect and for other reasons, it is unlikely that a within the light amplifier tube 431 as they were in previ pulse length shorter than several hundred cycles of the ous light amplifiers explained hereinabove. Accord light frequency can be obtained, no matter how long the ingly, light photons emitted within the light amplifier non-reflecting amplifier tube is made. tube 431 are not normally reflected to retraverse the 35 It should be noted that the operation of the nonre interior 435 of the light amplifier tube 431. Usually a flecting light amplifier tube comes somewhat more photon emitted will thus traverse less than the length of complex when the transition becomes "power broad the light amplifier tube before being transmitted to the shed'. These different effects are of consequence when exterior or absorbed. the time required for the wave-train length to pass a Accordingly, there is little opportunity for regenera given point is less than the phase relaxation time. The tive action within the light amplifier tube, and a consid various effects produced under this condition will not erable excess population of atoms (or ions or molecules) be discussed in detail. It will suffice to say that under in the upper two energy levels can be achieved and these conditions the pulse passing through the non-lin maintained without spontaneous regenerative oscilla ear light amplifier tube will continue to grow shorter tion in the light amplifier tube. 45 and denser. One minor effect is that the peaking action When this condition exists in the light amplifier tube on the input wave form will be somewhat delayed so 431, it is conditioned to act as an amplifier. Such a non that the peak will be formed somewhat behind the lead reflecting nonresonant light amplifier is capable of am ing edge of the input pulse wave-train. plifying light with a frequency bandwidth smaller than Short light pulses such as those obtained from the the corresponding transition bandwidth of the atoms, 50 pulsed resonant light amplifier and even shorter pulses ions, or molecules of the working medium, but larger obtainable from the non-reflecting light amplifier tube than the resonance response bandwidth of a resonant are useful for various purposes and in various systems, light amplifier. Also, wave-trains with non-planar wave some of which will later be explained in some detail. fronts may be coherently amplified. For example, a The apparatus of FIG. 7 by itself would be useful in diverging spherical wave may be amplified without 55 the field of high speed photography. The length of pulse changing its shape. Such a wave would not be accepted obtainable with apparatus as shown in FIG.7 may be as to a resonant light amplified with planar specular reflec short as the order of 10-12 seconds. The ability of a tors. Of course, a resonant light amplifier may be con pulse of this short length to "stop' action can be appre structed with reflectors of other than plane shape for ciated by the fact that an object traveling at the speed of amplifying non-planar waves. However, the more flexi light would be stopped within one millimeter by such a ble non-reflecting nonresonant amplifier is preferred for short pulse of light. this purpose. Although the total amount of light energy may be Although the light amplifier tube 431 would operate somewhat smaller than conventional photographic light as a substantially linear amplifier for low intensity light sources, this would not be a serious limitation, and par inputs, it is of more interest to consider the operation of 65 ticularly so in the field of microphotography, for exam the apparatus for relatively high intensity input pulses. ple, where only a small area need be illuminated. The By relatively high intensity, it is meant that the pulse fact that the output from the non-linear light amplifier intensity is sufficient to substantially depopulate the has very nearly plane waves makes it possible to focus 4,053,845 23 24 the output to as small an area as would be desired for length corresponding to said fluorescent emission tran microphotographic purposes. sition through said amplification region. 3. Light amplifier apparatus as defined in claim 2 in LIGHT ENERGY MACHINING APPARATUS which said bright pumping source is a source of broad In addition to the variations and modifications to band light energy. applicant's disclosed apparatus which have been sug 4. Light amplifier apparatus as defined in claim 2 in gested, many other variations and modifications will be which said medium is in a gaseous state. apparent to those skilled in the art and, accordingly, the 5. Apparatus for light amplification as defined in scope of applicant's invention is not to be construed to claim 1 in which said bright pumping light source emits be limited to the particular embodiments shown or sug 10 substantially no photon energy at a frequency substan gested but is rather to be limited solely by the appended tially corresponding to the emitted light due to transi claims. tions from the higher state to the lower state. What is claimed is: 6. Apparatus for light amplification as defined in 1. Apparatus for light amplification comprising a claim 1 in which said medium is in a gaseous state. bounded volume containing an excitable medium, the 15 7. Light amplifier apparatus as defined in claim 2 also atoms, ions or molecules of said medium having well including means to enable said medium to emit said light defined energy states including a lowest state, a lower when stimulated by said stimulating light in a wave state above said lowest state, and a higher state above train that has a sharply rising intensity with an intensity said lower state, and a bright pumping light source rise time of less than approximately 10-7 seconds. composed of a radiative substance different from said 20 8. Apparatus for light amplification as defined in medium which substance emits energy in a spectral claim 1 in which said bright pumping light source is a range which can be absorbed by said medium, the major gaseous discharge lamp. portion of the energy absorbed by said medium causing 9. Light amplifier apparatus as defined in claim 2 also transitions of the atoms, ions, or molecules thereof to including means for providing egress for amplified light populate the higher state, said bright pumping light 25 from said bounded volume. source being arranged to direct light into said medium 10. Apparatus for light amplification as defined in to excite said atoms, ions, or molecules to emit light claim 1 also including means for providing egress for photons in the bounded volume when stimulated to do said emitted light from said bounded volume. so by the presence of stimulating light at a frequency 11. Light amplifier apparatus comprising an excitable 30 medium of atoms, ions, or molecules, some of which substantially corresponding to the emitted light due to have broad bands of energy levels corresponding to a transitions from the higher state to the lower state, said broad band of absorption transitions and energy levels emitted light having substantially the same phase, fre corresponding to at least one fluorescent emission tran quency, polarization and wavefront shape as the stimu sition; the upper energy levels of said broadbands being lating light, thus adding coherently to the amplitude of 35 above the upper level of said fluorescent emission tran the stimulting light. sition, some of the upper energy levels above the upper 2. Light amplifier apparatus comprising an excitable level of said fluorescent emission transition being rap medium of atoms, ions, or molecules, some of which idly quenched via non-radiating transitions to the upper have broad bands of energy levels corresponding to a level of said fluorescent emission transition, and the broad band of absorption transitions and energy levels lower energy level corresponding to said fluorescent corresponding to at least one fluorescent emission tran emission transition being relaxed by non-radiating tran sition; the upper energy levels of said broadbands being sitions; and a bright pumping source of light energy for above the upper level of said fluorescent emission tran irradiating said medium to thereby excite at least a por sition, some of the upper energy levels above the upper tion of said medium to produce an amplification region level of said fluoroscent emission transition being rap 45 therein so that amplification of light by stimulated emis idly quenched via non-radiating transitions to the upper sion of radiation at a wavelength corresponding to said level of said fluorescent emission transition; and a bright fluorescent emission transition takes place in said re pumping source of light energy for irradiating said me gion; and means for conveying a stimulating light beam dium to thereby excite at least a portion of said medium having a wavelength corresponding to said fluorescent to produce an amplification region therein so that am 50 emission transition through said amplification region. plification of light by stimulated emission of radiation at 12. Light amplifier apparatus as defined in claim 11 a wavelength corresponding to said fluorescent emis also including means for providing egress for amplified sion transition takes place in said region; and means for light from said bounded volume. conveying a stimulating light beam having a wave k x k 55 65 UNITED STATES PATENT OFFICE Page 1 of 3 CERTIFICATE OF CORRECTION Patent No. 4,053,845 Dated Oct. ll, 1977 Inventor(s) Gordon Gould It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: Column l, line 43, "Planok's" should be --Planck's--. Column 2 lines 44-45, the formula should read h N,h - N,l 8T2p2 to Line 48 "T" should read -- I -- . Lines 59-60, the formula should read N - N 2 h h 1. 4T4p22 'unloaded Column 6 line 36, the word "latter" should read --letter--. Column 7 line l6, the word "amplification" should read --amplification--. Column 8 line l7, "XT" should read --KT--. Line 21, " (63F)" should read -- (63P)--. UNITED STATES PATENT OFFICE Page 2 of 3 CERTIFICATE OF CORRECTION Patent No. 4,053,845 Dated Oct. 1, 1977 Inventor(s) Gordon Gould It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: Column l5, lines 64-69, the expressions for the "COINCIDENT" ATOMIC SPECTRAL LINES in TABLE III should read as follows: He (3P + 2s) 3889A*-CsAP (8P/2 - 6s2)3889A3- , , Zn w 3303.7As Na (42P1/2 - 3° S) 3303A A. 8521.4A*Cs (62P1/2 - 6° S) 852l. 2A Column l6, lines 66-68, the portion of the equation reading Pavail should read Pavail l hW lines 2-3, the formula should read: din = 0 = A (h -)- ) - in C Lines 8-9, the equation should read: h = Yc n1 A (h. -- 1) Column l7, line 28, the ">" should read --> --. UNITED STATES PATENT OFFICE Page 3 of 3 CERTIFICATE OF CORRECTION Patent No. 4,053, 845 Dated Oct. Ill., 1977 Inventor(s) Gordon Gould It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: Column l8, line 43, "Y = 2.5" should read -- Y - 1.5 --. Column l9, line 9, "medium" should read --mediums--. Line 37, "are" should read --and-- Line 45, "6" should read --7--. Line 46-47, "42l and the description thereof." should read -- 4:21.--. Column 20 line 46, "l6" should read --7--. Column 22, lines 37-38, "power broadshed" should read --power broadened--. Column 23 lines 3-4, "LIGHT ENERGY MACHINING APPARATUS" should be deleted. signed and Sealed this Thirty-first Day of October 1978 SEAL Attest: RUTH (C. RASON (ONALD W. BANNER Attesting Officer Copper sissioner of Pater its aid Trégalenarks REEXAMINATION CERTIFICATE (670th) United States Patent (19) 11 B1 4,053,845 Gould 45 Certificate Issued Apr. 28, 1987 54) OPTICALLY PUMPED LASER AMPLIFIERS “The Dazzle of Lasers', Newsweek, Jan, 3, 1983, pp. 36-40, 76) Inventor: Gordon Gould, 329 E. 82 St., New “Sun Guns", Omni, May 1982, pp. 61-64, 94-95. York, N.Y. 10028 "Solid State Optical Maser Using Divalent Samarium', P. P. Sorokin and M. J. Stevenson, IBM Journal of Reexamination Requests: Research and Development, Jan. 1961, pp. 56-58. No. 90/000,253, Sep. 9, 1982 "On the Quantum Theory of Radiation", A. Einstein, No. 90/000,254, Sep. 9, 1982 Physikalische Zeitschrift, vol. 18, 1917. No. 90/000,336, Mar. 4, 1983 "Organic Laser Systems', A. Lempicki and H. Samel son, Lasers, vol. 1, Chapter 3, 1966, pp. 181-252. Reexamination Certificate for: "Infrared Fluorescence and Stimulated Emission of Patent No.: 4,053,845 Ndt-3 in CaWO4', L. F. Johnson and K. Nassau, Pro Issued: Oct. 11, 1977 ceedings of IRE, Nov. 1961, pp. 1704-1706. Appl. No.: 498,065 "Stimulated Infrared Emission From Trivalent Ura Filed: Aug. 16, 1974 nium", P. P. Sorokin and M. J. Stevenson, Physical Certificate of Correction issued Oct. 31, 1978. Review Letters, Dec. 15, 1960, pp. 557-559. "Crystalline Solid Lasers", Z. J. Kiss and R. J. Pressley, Proceedings of IEEE, vol. 54, Oct. 1966, pp. Related U.S. Application Data 1236-1248. 60 Continuation of Ser. No. 644,035, Mar. 6, 1967, aban General Electric Price Schedule, Form 21 15, Re Na-l doned, and Ser. No. 804,540, Apr. 6, 1959, abandoned, Sodium Lamp, Feb. 1, 1960 (Supercedes Form 21 15 said Ser. No. 644,034, is a division of said Ser. No. dated Jul. 1, 1957). 804,540, and a continuation-in-part of Ser. No. 804,539, Introduction to Lasers and Their Applications, D. C. O'- Apr. 6, 1959. Shea et al., 1977, pp. 13–14. 51) Int. Cl.' ...... H01S 3/091; H01S 3/22 Lamps and Lighting, S. T. Henderson and A. M. Mars 52 U.S. C...... 330/4.3; 372/55; den, 1972, Chapter 13, Sodium Lamps, pp. 234-249. 372/70; 372/91 "Incoherent Optical Sources', I. Liberman, Handbook 58) Field of Search ...... 372/51, 56, 55, 70, of Lasers, 1971, pp. 13-38. 372/91, 40; 324/304,305 (List continued on next page.) 56) References Cited U.S. PATENT DOCUMENTS Primary Examiner-Harvey E. Behrend 1, 195,923 8/1916 Gans . 57 ABSTRACT 1,716,962 6/1929 Johnson . 1,815,733 7/193i Gulick . Optically pumped laser amplifiers are disclosed. One 2,851,652 9/1958 Dicke . type of such amplifier utilizes an excitable medium, the 2,884,524 4/1959 Dicke. atoms, ions or molecules of said medium having well 2,909,654 10/1956 Bloembergen. defined energy states including a lowest state, a lower 2,929,922 3/1960 Schawlow et al. . state above said lowest state, and a higher state above 3,403,349 9/1968 Wieder . said lower state, and a bright pumping light source 3,609,570 9/1971 Gould . composed of a radiative substance different from such 3,614,653 10/1971 Javan et al. . medium which radiative substance emits energy in a FOREIGN PATENT DOCUMENTS spectral range which can be absorbed by such medium, 953271 4/1964 United Kingdom . and wherein the major portion of the energy absorbed 953272 4/1964 United Kingdom . by such medium causes transitions of the atoms, ions, or 953273 4/1964 United Kingdom . molecules thereof to populate the higher state. Another 953274 4/1964 United Kingdom . type of such amplifier utilizes a medium of atoms, ions, 953275 4/1964 United Kingdom . or molecules, some of which have broad bands of en 95.3276 4/1964 United Kingdom. ergy levels corresponding to a broadband of absorption 953721 4/1964 United Kingdom. transitions and energy levels corresponding to at least OTHER PUBLICATIONS one fluorescent emission transition, the upper energy levels of said broad bands being above the upper level "Infrared and Optical Masers', A. L. Schawlow and C. of said fluorescent emission transition, and wherein H. Townes, Physical Review, vol. 112, Dec. 15, 1958, some of the upper energy levels above the upper level pp. 1940-1949. of said fluorescent emission transition are rapidly "Infrared and Optical Masers', A. L. Schawlow and C. quenched via non-radiating transitions to the upper H. Townes, Preprint of 112 Physical Review 1940. level of said fluorescent emission transition. In a pre "Resonance And Quenching Of The Third Principal ferred embodiment of the latter amplifier, the lower Series Line Of Caesium', C. Boeckner, Bureau of Stan energy level corresponding to the fluorescent emission dards Journal of Research, vol. 5, 1930, pp. 13-18. transition is relaxed by non-radiating transitions. B1 4,053,845 Page 2 OTHER PUBLICATION "Stimulated Emission Observed from an Organic Dye, Chloro-aluminum Phthalocyanine', P. P. Sorokin and “The 'Speckle" On A Surface Lit By Laser Light Can J. R. Lankard, IBM Journal, Mar. 1966, pp. 162-163. Be Seen With Other Kinds Of Illumination', The Ama “Possibility Of Obtaining Negative Temperature In teur Scientist, J. Walker, Scientific American, vol. 246, Atoms By Electron Impact', A. Javan, Quantum Elec No. 2, Feb. 1982, pp. 162-169. tronics Conference, Sep. 14-16, 1959, pp. 564-571. “High-Pressure Sodium Discharge Arc Lamps', W. C. "Coherent Light Amplification in Cs Vapor', S. Ja Louden and K. Schmidt, Illuminating Engineering, vol. cobs, G. Gould and P. Rabinowitz, TRG, Syosset, N.Y. LX, No. 12, Dec. 1965, pp. 696-702. Laser-pumped Stimulated Emission from Organic Practical Spectroscopy, G. R. Harrison, R. C. Lord, and Dyes: Experimental Studies and Analytical Compari J. R. Loofbourow, 1948, (selected pages). sons', P. P. Sorokin, J. R. Lankard, E. C. Hammond, "Pulsed Alkali-Vapor Lamps', J. E. Creedon, W. and V. L. Moruzzi, IBM Journal, Mar. 1967, pp. Bayha and S. Schneider, Research and Development 130-48. Technical Report ECOM-3051, Dec. 1968, AD 680846, "Emission Spectrum Of Rhodamine B Dye Lasers', T. United States Army Electronics Command, Fort Mon F. Deutsch, M. Bass, and P. Meyer, and S. Protopapa, mouth, N.J. Applied Physics Letters, vol. 11, No. 12, Dec. 15, 1967, “A Tunable Laser Using Organic Dye Is Made At pp. 379–381. Home For Less Than $75', The Amateur Scientist, C. "New Dye Lasers Covering The Visible Spectrum', F. L. Stong, Scientific American, vol. 222, No. 2, Feb. P. Schafer, W. Schmidt and K. Marth, Physics Letters, 1970, pp. 116-120. vol. 24A, No. 5, Feb. 27, 1967, pp. 280-281. “Organic Lasers', P, Sorokin Scientific American, vol. "Inversion Mechanism in Gas Lasers', W. R. Bennett, 220, No. 2, Feb. 1969, pp. 30-40. Jr., Applied Optics, Supplement 2: Chemical Lasers, Reference Data for Radio Engineers, Third Edition, Fed 1965, pp. 3-33. eral Telephone and Radio Corporation, 1949, p. 90. "Population Inversion And Continuous Optical Maser “Flashlamp-Pumped Organic-Dye Lasers", P. P. Soro Oscillation. In A Gas Discharge Containing A He-Ne kin, J. R. Lankard, V. L. Moruzzi, and E. C. Hammond, Mixture', A. Javan, W. R. Bennett, Jr., and D. R. Her Journal of Chemical Physics, vol. 48, No. 10, May 15, riott, Physical Review Letters, vol. 6, No. 3, Feb. 1, 1968, pp. 4726-4741. 1961, pp. 106-110. "Frequency- And Time-Dependent Gain Characteris "Laser Work At Technical Research Group', G. tics of Laser- and Flashlamp-Pumped Dye Solution Gould and L. Goldmuntz, National Aerospace Elec tronics Conference, May 14-16, 1962, pp. 190-193. Lasers', M. Bass, T. F. Deutsch, and M. J. Weber, "Alkalai Vapor Infrared Masers', C. H. Townes et al., Applied Physics Letters, vol. 13, No. 4, Aug. 15, 1968, Advances in Quantum Electronics, Mar. 23-25, 1961, pp. 120-124. pp. 12-17. “Organic Dye Lasers', Morton R. Kagan, Gerald I. "Coherent Light Amplification. In Optically Pumped Farmer and Bernard G. Huth, Laser Focus, Sep. 1968, pp. 26-33. Cs Vapor'. S. Jacobs, G. Gould and P. Rabinowitz, "A-2-Experimental Measurement of the Critical Pop Physical Review Letters, vol. 7, No. 1 1, Dec. 1, 1961, ulation Inversion for the Dye Solution Laser", B. B. pp. 415-417. Snavely and O. G. Peterson, IEEE Journal of Quantum Industrial Applications of Lasers, J. F. Ready, 1978, Electronics, vol. QE-4, No. 10, Oct. 1968, pp. 540-545. Chapter 14, pp. 358-366. "Time Dependent Spectroscopy Of Flashlamp Pumped "Laser Oscillations In Nd-Doped Yttrium Aluminum, Dye Lasers', H. Furumoto and H. Ceccon, Applied Yttrium Gallium, and Gadolinium Garnets', J. E. Geu Physics Letters, vol. 13, No. 10, Nov. 15, 1968, pp. sic et al., Applied Physics Letters, vol. 4, No. 10, May 335-337. 15, 1964, pp. 182-184. “Lasers Based On Solutions Of Organic Dyes', B. l. Lasers, B. A. Lengyel, 1971, pp. 39-59. Stepanov and A. N. Rubinov, Soviet Physics Uspekhi, "Liquid Lasers: Promising Solutions', H. Samelson, vol. 11, No. 3, Nov.-Dec. 1968, pp. 304-319. Electronics, Nov. 11, 1968, pp. 142-147. General Electric Lamp Bulletin LD-1, Jan., 1956. "Fine Structure and Properties of Chromium Fluores "Frequency- and Time-Dependent Gain Characteris cence in Aluminum and Magnesium Oxide', A. L. tics of Dye Lasers", Marvin J. Weber and Michael Bass, Schawlow, Advances in Quantum Electronics, Mar. IEEE Journal Of Quantum Electronics, vol. QE-5, No. 23-25, 1961, pp. 50-64. 4, Apr. 1969, pp. 175-188. "Optical Maser Action of Ndl3 In A Barium Crown Dye Lasers, F. P. Schafer, Topics in Applied Physics, Glass', E. Snitzer, vol. 7, No. 12, Dec. 15, 1961, pp. 444-446. vol. 1, Second Edition, 1977, (selected pages). "Optical and Laser Properties of Nd+ 3 and Eu+3 "Flashlamp-Excited Organic Dye Lasers', Benjamin Doped YVO4', J. R. O'Connor, Transactions of Metal B. Snavely, Proceedings Of The IEEE, vol. 57, No. 8, lurgical Society of AIME, vol. 239, Mar. 1967, pp. Aug. 1969, pp. 1374-1390. 362-365. "Gas Lasers', C. K. N. Patel, Lasers, vol. 2, Chapter 1, "Fluorescence and Stimulated Emission from Trivalent 1968, pp. 1-36. Europium in Yttrium Oxide', N. C. Chang, Journal of Gas Lasers, C. G. B. Garrett, 1967, pp. 59-62. Applied Physics, vol. 34, No. 12, Dec. 1963, pp. The Laser, W. V. Smith and P. P. Sorokin, 1966, Chap 3500-3504. ters 2 and 5. (List continued on next page.) B1 4,053,845 Page 3 OTHER PUBLICATION "Optically Detected Field-Independent Transition. In Sodium Vapor", W. E. Bell and A. L. Bloom, vol. 109, "Advances In Laser Technology", Gordon Gould, post Jan. 1, 1958, pp. 219–220. 1971, pp. 85-93. "K13. Optically Detected Magnetic Resonance in Ru "Optically Pumped Pulsed Crystal Lasers Other Than bidium Vapor", W. E. Bell and A. L. Bloom, Bulletin of Ruby', L. F. Johnson, Lasers, vol. 1, Chapter Two, American Physical Society, Ser. II. vol. 2, No. 8, Dec. 1966, pp. 137-180. 19, 1957, p. 384. "Simultaneous Optical Maser Action In Two Ruby "K14. Optically Detected Hyperfine Resonances in Satellite Lines', A. L. Schawlow et al., Physical Re Potassium Vapor", A. L. Bloom and W. E. Bell, Bulle view Letters, vol. 6, No. 3, Feb. 1, 1961, pp. 96-98. tin of American Physical Society, Ser. II, vol. 2, No. 8, "Light of the 21st Century”, NOVA, Public Television, Dec. 19, 1957, p. 384. 1978, p. 15. "J3. Optical Detection of the Cesium Hyperfine Split "Optical Detection Of Paramagnetic Resonance In An ting', E. C. Beaty and P. L. Bender, Bulletin of Ameri Excited State Of Cr3+ In Al2O3', A. L. Schawlow et can Physical Society, Ser. II, vol. 3, No. 3, May 1, 1958, al., Physical Review Letters, vol. 3, No. 12, Dec. 15, p. 185. 1959, pp. 545-548. Press Release and Speech by T. H. Maiman as to "Electronic Spectra Of Exchange-Coupled Ion Pairs In Achievement of Ruby Laser, Jul. 7, 1960, Crystals', A. L. Schawlow et al., Physical Review General Electric Bulletin TP-109R, "High Intensity Letters, vol. 3, No. 6, Sep. 15, 1959, pp. 271-273. Discharge Lamps', 1975. "Laser Survey', S. Rothberg, TRG Technical Note "Stimulated Optical Emission. In Fluorescent Solids, I. #48, May 11, 1962, pp. 1-4. Theoretical Considerations, II. Spectroscopy And "Payday For The Laser's Creator', Business Week, Stimulated Emission. In Ruby', T. H. Maiman et al., Dec. 14, 1981, p. 122B. Physical Review, Vol. 123, August 15, 1961, pp. "A Study of the Line Spectrum of Sodium as Excited 1145-1157. by Fluorescence', Hon. R. J. Strutt, Proceedings of "Molecular Generator And Amplifier", N. G. Basov Royal Society of London, vol. XCVI, Feb. 1920, pp. and A. M. Prokhorov, Uspekhi Fizicheskikh Nauk, 272-287. Vol. 57, No. 3, 1955, pp. 485-501. "Laser Action in Rare Earth Chelates', A. Lempicki, "Optical Methods of Atomic Orientation and of Mag H. Samelson, and C. Brecher, Applied Optics, Supple netic Resonance', A. Kastler, Journal of Optical Socie ment 2: Chemical Lasers, 1965, pp. 205-213. ty of America, Vol. 47, No. 6, June 1957, pp. 460-465. "Lasers Action in Liquids', A. Heller Physics Today, Bibliography of Articles Pertinent to Laser Program at vol. 20, Nov. 1967, pp. 35-41. TRG, Contract no. AF 49 (638)-673, Report No. Resonance Radiation and Excited Atoms, A. C. G. TRG-134-TR-3, July 23, 1960, pp. 208-236. Mitchell and M. W. Zemansky, 1934 (selected pages). "Stimulated Optical Radiation in Ruby', T. H. Mai Molecular Spectra and Molecular Structure, G. Herz man, Nature, August 6, 1960, pp. 493-494. berg, 1950, p. 122. "Optical Maser Action in Ruby", T. H. Maiman, Brit "The Excitation Of Sodium By Ionized Mercury Va ish Communications and Electronics, September 1960, por", H. W. Webb and S. C. Wang, Physical Review, pp. 674-675. vol. 33, Mar. 1929, pp. 329-340. "hfs Separations and hfs. Anomaly in the 6P is Meta Atomic Spectra and Atomic Structure, G. Herzberg, stable Level of T1 and T10", Gordon Gould, Physi 1944, p. 72. cal Review, Vol. 101, January 1-March 15, 1956, pp. "Continuous Optically Pumped Cs Laser", P. Rabino 1828-1829. witz, S. Jacobs and G. Gould, Applied Optics, vol. 1, "Optical Pumping", A. L. Bloom, Scientific American, No. 4, Jul. 1960, pp. 513-516. October 1960, pp. 72-80, 220. "Solid-State, High-Intensity Monochromatic Light "Scalpels of Light", Life, May 1982, pp. 129-134. Sources', I. Wieder, Review of Scientific Instruments, "Molecular Microwave Oscillator and New Hyperfine vol. 30, No. 11, Nov. 1959, pp. 995-996. Structure in the Microwave Spectrum of NH3", J. P. "Slow Spin Relaxation Of Optically Polarized Sodium Gordon, H. J. Zeiger and C. H. Townes, Physical Atoms", H. G. Dehmelt, Physical Review, vol. 105, Review, Vol. 95, 1954 pp. 282-284. No. 5, Mar. 1, 1957, pp. 1487-1489. "Some Microwave-Optical Experiments In Ruby', I. "Possible Methods of Obtaining Active Molecules for a Molecular Oscillator', N. G. Basov and A. M. Prok Wieder, Quantum Electronics Conference, Sep. 14-16, horov, Soviet Physics JETP, Vol. 1, July 1955, pp. 1959, pp. 105-109. 184-185. "Atomic Orientation by Optical Pumping", W. Franzen "The Maser-New Type of Microwave Amplifier, and H. G. Emslie, vol. 108, No. 6, Dec. 15, 1957, pp. Frequency Standard, and Spectrometer", J. P. Gordon, 1453-1458. H. J. Zeiger, and C. H. Townes, Physical Review, Vol. "A Possible Limitation On Optical Pumping In Solids", 99, 1955, pp. 1264-1274. I. Wieder, Ann Arbor Conference on Optical Pumping, "Molecular Amplification and Generation of Micro Jun, 15-18, 1959, pp. 133-138. waves', J. P. Wittke, Proceedings of IRE, March 1957, "A Microwave Frequency Standard Employing Opti pp. 291-316. cally Pumped Sodium Vapor", W. E. Bell, A. Bloom, Fluorescence And Phosphorescence, P. Pringsheim, 1949 R. Williams, IRE Transactions on Microwave Theory (selected pages). and Techniques, Jan. 1959, pp. 95-98. (List continued on next page.) B1 4,053,845 Page 4 OTHER PUBLICATION A. L. Schawlow and C. H. Townes, preprint of "Infra red and Optical Masers', Physical Review, 112, 1940, C. Boeckner, "Resonance and Quenching of the Third (1958), preprint distribution beginning in the summer of Principle Series Line of Cesium', Bureau of Standards 1958. Journal of Research, 5, 13, (1930) A. L. Schawlow and C. H. Townes, "Infrared and Optical Masers", Physical Review, 112, 1940, (Dec. 15, G. H. Dieke and Shoba Singh, "Absorption, Fluores 1958). cence and Energy Levels of the Dysprosium Ion', "Stimulated Emission from Ho' at 2 microns in HoF3, Journal of the Optical Society of America, 46(7), 495 D.P. Devor et al., Applied Physics Letters, 18(4), 122 (1956) (1971). B1 4,053,845 1 2 REEXAMINATION CERTIFICATE AS A RESULT OF REEXAMINATION, IT HAS ISSUED UNDER 35 U.S.C. 307 BEEN DETERMINED THAT: 5 The patentability of claims 1-12 is confirmed. NO AMENDMENTS HAVE BEEN MADE TO THE PATENT st it st sk k O 15 20 25 35 45 50 55 60 65