Europaisches Patentamt number: 0191856 J) European Patent Office Publication B1 Office europeen des brevets

EUROPEAN PATENT SPECIFICATION

Date of publication of patent specification: 30.08.89 Intel.4: H 01 S 3/125 Application number: 85904897.7

Date of filing: 24.07.85 International application number: PCT/US85/01409

International publication number: WO 86/01347 27.02.86 Gazette 86/05

A CO2 TEA LASER UTILIZING AN INTRA-CAVITY PRISM Q-SWITCH.

Priority: 02.08.84 US 637097 Proprietor: Hughes Aircraft Company 7200 Hughes Terrace P.O. Box 45066 Los Angeles, California 90045-0066 (US) Date of publication of application: 27.08.86 Bulletin 86/35 Inventor: DEWHIRST, Donald, R. 4822 White Court Publication of the grant of the patent: Torrance,CA 90503 (US) 30.08.89 Bulletin 89/35 Inventor: DUVALL, Robert, L, III 2649 West 233 Street Torrance, CA 90505 (US) Designated Contracting States: BECHDEFRGBITLINLSE Representative: Kuhnen, Wacker & Partner Schneggstrasse3-5 Postfach 1553 References cited: D-8050 Freising (DE) FR-A-1 537 891 FR-A-2331801 US-A-3434073 References cited: US-A-3548253 Japanese Journal of Applied Physics, volume CO US-A-3 609 588 7, no. 12, December 1968, Tokyo, (JP). Y. US-A-3 725 817 Ohtsuka et al.: "ACO2 Q-switched laser and its CO US-A-3 995 230 nonlinear amplification characteristics", pages in US-A-4355394 1510-1517 00 Applied Physics Letters, volume 8, no. 3, 1 February 1966, New York (US). G.W. Flynn et 5> al.: "Vibrational and rotational studies using Q-switching of molecular gas lasers", pages 63-65 o Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall Q. be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been Ill paid. (Art. 99(1 ) European patent convention). Courier Press, Leamington Spa, England. EP 0 191 856 B1 Description output. The difficulty of creating the discharge in the higher pressure gas is offset by the reduced Background of the invention path length of the transverse discharge. The high 1. Field of the invention peak power of the CO2 TEA laser is not accom- The present invention relates to a rotating 5 plished by a Q-switch, but results from the fast prism Q-switch for use with CO2TEA (carbon discharge which causes the gain to build up faster dioxide transversely excited atmospheric) lasers. than the laser pulse. This method is called "gain The rotating prism Q-switch angularly sweeps switching". through alignment with the resonator mirrors The fast discharge method is undesirable for once per revolution. An opto-electronic timing io many laser applications because sufficient nitro- device with imaging optics rotating with the gen excitation remains after the initial laser pulse prism triggers the gas discharge at the proper to sustain laser oscillation at a power level 1/10 to time prior to resonator alignment. 1/4 of the peak. The output energy after the main pulse is referred to as the "tail" and typically 2. Description of related art 15 contains more than half the energy and lasts up to The CO2 laser has long been available and can several microseconds. In laser range finder be configured to produce a continuous or pulsed applications, the tail is backscattered into the laser beam. It is capable of high average power receiver, thus "blinding" the receiver for the few output while at the same time maintaining the microseconds that the tail exists, which blinding high degree of spectral purity and spatial coher- 20 is unacceptable. ence, characteristics of the lower power atomic The tail can be eliminated by the addition of a gas lasers. An electric discharge is the most Q-switch wherein the Q-switch is on for the main common means of excitation. Operating effi- pulse, and then turned off to prevent the tail. The ciency and output power are greatly increased by Q-switch also can increase the peak output power adding nitrogen and helium to the fill gas. Helium 25 by delaying the switch opening so that the laser aids depopulation of the terminal laser level and pulse occurs near peak gain. For the gain nitrogen excites the carbon dioxide molecules by switched laser, the pulse can occur well before collisional energy transfer. To facilitate the dis- peak gain, thus increasing the tail energy. charge, the CW (continuous-wave) excited CO2 From US— A— 3 434 073 a mechanically Q- laser is operated at low pressure, on the order of 30 switched laser is known in which the timing pulse 13.3 kPa (100Torr). for triggering excitation of the laser medium is Because of the long lifetime of the vibration generated by directing a light beam to the rotat- levels, it is possible to store energy in the dis- ing prism Q-switch and the light beam reflected charge medium by blocking the path of the laser from the prism Q-switch hits a photodetectoronly beam within the resonator, thereby preventing 35 if the prism Q-switch is in a certain position. the laser oscillation. If the block is suddenly From US — A — 3 548 253 an apparatus for con- removed, then the output from the laser occurs in trolling the resonator gain of a pulse laser device the form of a sharp pulse with peak power two to is known, which is the basis for the preamble of three orders of magnitude larger than the average claim 1. Said known apparatus comprises means continuous-wave power obtainable from this 40 for rotating a prism Q-switch whereby resonator laser. This mode of operation is called Q-switch- mirrors of the laser are angularly aligned periodi- ing. In a typical prior art device in which the gas is cally by the rotating prism and an optical imaging excited by CW discharge, Q-switching is accom- device including a photodetector, a light source, plished by replacing one of the laser cavity and an optical guideway coupled to said rotating mirrors with a rotating mirror. A laser pulse at 45 means for optically coupling light from the light 10.6 microns is produced every time the rotating source to the photodetector. The optical pathway mirror lines up with the opposite stationary is a hole in a drum which rotates together with the mirror. prism Q-switch. The photodetector and the light A more efficient method of producing high peak source are arranged such that once per revolution power pulses from the CO2 TEA laser is the use of so of the rotating means the light source and the a pulsed high voltage discharge in a gas medium photodetector are optically coupled. at much higher pressure. As is known, a C02 TEA Since the CO2 TEA laser has an excited state (transversely excited atmospheric) laser is a type lifetime of only a few microseconds, a timing of C02 laser in which excitation of the active accuracy of a few hundred nanoseconds is medium is transverse to the laser beam axis and, 55 required for the time delay between the gas because of a shorter breakdown length, can oper- discharge and Q-switch opening. Heretofore, only ate in a gas pressure range higher than that for the electro-optic Q-switch was capable of provid- longitudinally excited gas lasers, thus achieving a ing this degree of timing accuracy. However, the higher power output per unit volume because of electro-optic Q-switch has serious disadvantages the greater density of lasing molecules. In this 60 when used with C02 TEA lasers due to its cost, laser the gas pressure is near one atmosphere complexity, fragility and susceptibility to laser and the discharge is very fast and transverse to damage. the beam axis. By operating at higher pressure, What is desired is an arrangement wherein a Q- the density of excited CO2 molecules is increased, switch can be utilized with the CO2TEA laser thereby proportionally increasing the peak power 65 without the aforementioned disadvantages of the EP 0 191 856 B1 schematic of the electro-optic Q-switch, the timing accuracy Fig. 4 is a simplified optical the required for laser operation still being provided. components which comprise opto-electronic timing device of the present invention; the Summary of the invention Fig. 5 is a timing diagram illustrating trig- of the These problems are overcome with an gering pulse timing to initiate lasing shown in 3 and the resultant apparatus controlling the resonator gain of a CO2 TEA laser Fig. and pulse laser device in accordance with claim 1. laser pulse output; An embodiment of the present invention pro- Figs. 6a and 6b are reproductions of photo- shape vides a CO2 TEA type laser which is adopted to graphs of CO2TEA laser temporal pulse 6a) and Q- with a simple rotating prism Q-switch. 10 respectively gain switched (Fig. operate 200 The Q-switch is interposed switched (Fig. 6b), both of whose scales are rotating prism KW between the laser resonator mirrors and is nanoseconds per division horizontally and 60 arranged such that rotation of the Q-switch per division vertically. reference numerals identify identical sweeps the resonator mirrors through alignment The same with one another once each revolution of the Q- 15 components in each of the figures. switch. The speed of rotation is selected so that the time interval of good resonator alignment is Detailed description of the invention sufficient to allow for the main pulse buildup, but For purposes of understanding the background discussion of of not long enough to support the tail. of the present invention, a some will be An opto-electronic timing device provides a 20 the prior art CO2 laser arrangements prealignment signal to initiate the gas discharge useful. about 4 microseconds prior to resonator Fig. 1 shows a prior art continuous wave high Imaging optics of the timing device power carbon dioxide laser 8 modified to operate alignment. mirror. comprise a graded index fiber optic rod mechan- in the Q-switching mode by a rotating laser in ically attached to and rotating with the Q-switch 25 The advantages of operating a C02 type been described here- prism. A timing pulse is generated by the timing the Q-switching mode has the device once every revolution of the rotating inabove with reference to background por- The simultaneous presence of a laser tion of this application. In essence, Q-switching prism. much enable signal and the timing pulse initiates the provides laser output pulses having a to produce a laser pulse. Thus, the 30 higher peak power than provided by operating a gas discharge As PRF is controlled by the laser enable signal. The C02 laser in the continuous wave mode. relative angular position of the fiber optic rod illustrated in Fig..1, Q-switching is accomplished mirrors and prism is selected such that the resonator by replacing one of the laser resonator mirrors are swept into alignment at near peak with a rotating mirror 10. In the simplified ver- 35 sion shown, laser 8 additionally includes a Bews- gain. coolant In a preferred embodiment of the invention, ter window 12. Pyrex tubing 13, a 16 the Q-switch prism is arranged to fold the (usually water) contained within an enclosure resonator into a "U" configuration so that the having inlet and outlet ports 18 and 20, respec- resonator mirrors can be placed close together tively, gas inlet ports 22 and 24, respectively, a mirror 27. A for alignment stability. Further, the prism 40 flexible bellows 25 and an output is between elec- geometry is chosen to make the resonator source of potential 28 coupled insensitive to small angular tilts of the trodes 29 and 30 in series with a resistor 32. A alignment and prism about axes perpendicular to the axis of premixed gas, typically comprising CO2, N2 rotation. Other advantages of the rotating prism He, is introduced into tubing 13 through inlet and Q-switch compared to the electro-optic switch 45 port 22. Mirror 27 is dielectrically coated of 10.6 microns. are simplicity, insensitivity to temperature and transmits laser radiation 31 durability. In operation, mirror 10 is caused to rotate so that optical alignment of mirrors 10 and 27 train of Brief description of the drawings occurs periodically. The continuous high useful for certain For a better understanding of the invention as so peak power laser pulses are well as further features and objects thereof, ref- cutting and machining operations, optical com- is made to the following description munications and optical radar. erence fast which is to be read in conjunction with the Fig. 2 illustrates a C02TEA laser 40 using of accompanying drawings wherein: discharge electric excitation. For purposes and outlet Fig. 1 is a simplified cross-sectional view of a 55 simplicity, the gas coolant inlet ports art continuous wave CO2 laser modified to and cooling devices (if any) have not been illus- prior and/or use a rotating reflector as a Q-switch to produce trated. Laser 40 may use water cooling heat for a train of pulsed laser outputs; circulate the gas through a exchanger Fig. 2 is a simplified cross-sectional view of a high pulse repetition frequency (PRF) operation. prior art C02TEA laser modified to use an elec- 60 The laser gas mixture is introduced to Pyrex tro-optic Q-switch; tubing 42 at or near one atmospheric pressure. electrodes 44 Fig. 3 is a partial cross-sectional view of a Laser 40 supports parallel plate 48 and 50 CO2 TEA laser which utilizes a rotating prism Q- and 46 and has ceramic capacitors switch in accordance with the teachings of the mounted at each end. A pre-ionization trigger 48 and 50. A present invention; 65 wire 52 extends between capacitors EP 0 191 856 B1 fully reflecting mirror 54 and a partially reflecting between mirrors 54 and 56 is reflected by the mirror 56 are arranged adjacent to the ends of inclined surfaces 73 and 74 of prism 70 in a laser 40 to form the optical resonator cavity. Laser manner such that prism 70 folds the resonator output 58 at 10.6 microns is transmitted by output into a "U" configuration. In the preferred embodi- mirror 56. 5 ment, the folded resonator permits mirrors 54 and In operation, a trigger generator 62 energizes 56 to be positioned close together for alignment high voltage pulses in a pulser 64, the output of stability. For example, mirrors 54 and 56, which is applied to metal electrode 44. A high although shown as separate components, can be voltage pulse produced by pulser 64 ionizes the combined into a single mirror formed within a gas within tubing or envelope 42 causing a glow 10 rigid frame member, one portion of the mirror discharge to occur, the glow discharge causing having a partially transmitting coating, and the the active medium (C02 molecules in this case) to other portion of the mirror having a totally reflect- be excited to a population inversion condition to ing coating. Thus, if the frame containing the provide for laser operation. Trigger generator 62 single mirror is subjected to thermal or mechani- also activates a high voltage pulse generator 67 to 15 cal stresses, the same change in alignment is apply a high voltage pulse to an optical shutter transmitted to both mirror portions, to effectively device 68 after a time delay provided by a time cancel out any stress-caused misalignment of the delay device 66. Optical shutter device 68 is the laser resonator. The prism geometry is chosen to electro-optic Q-switch described hereinabove and make the resonator alignment unaffected by is effective to prohibit transmission of the laser 20 small angular displacements of the prism about light within the laser resonator, formed by mirrors its nonrotating axes. For example, if prism 70 is 54 and 56, unless it is turned on. Shutter 68 displaced to the position shown by the dashed typically comprises a CdTe electro-optical crystal lines, the relative angular alignment between with polarizers 69 at each end. Shutter 68 trans- incident and reflected rays are unchanged. Since mits laser light at 10.6 microns when a high 25 resonator mirrors 54 and 56 are swept through voltage pulse from H.V. pulse generator 67 is alignment with each other about the prism rota- applied thereto, such high voltage typically being tion axis, the resonator alignment is not affected a pulse of fixed time duration. Time delay 66 is by small angular tilts of mirrors 54 and 56 if they predetermined, and chosen to open shutter 68 to are moved as a single mirror relative to the prism. produce the laser pulse at a time when the gain 30 Fig. 4 shows an opto-electronic timing device medium is near maximum gain, thereby produc- 79 constructed in accordance with the teachings ing the maximum peak output power. The time of the present invention. A significant difference duration of the high voltage pulse applied to exists between the electro-optic and rotating shutter 68 is chosen to close shutter 68 just after prism Q-switches in which, for the prism switch, a the main pulse, thereby prohibiting the low inten- 35 laser pulse can only occur at times in which the sity tail that normally would follow. Although prism is aligned with the resonator mirrors. Tim- accurate timing can be provided by the combina- ing device 79 generates a prealignment signal to tion of delay element 66 and shutter 68, this trigger the discharge at the proper time before combination is rarely used for C02TEA lasers prism alignment. The required lead time for a because of the cost, complexity, fragility and 40 CO2 TEA laser typically is about 4 microseconds susceptibility to laser damage of the electro-optic with 10% maximum variation (repeatability of shutter 68 and polarizer 69. pulse initiation time) to minimize the shot-to-shot Fig. 3 illustrates the C02 TEA laser shown in Fig. variance of the output power. Prior to the present 2 modified in accordance with the teachings of invention, a rotating prism Q-switch was not the present invention. It should be understood, 45 capable of being used in C02 TEA lasers because however, that, although the present invention is of the gas discharge timing problem. described with CO2 TEA lasers, the invention can Timing device 79 comprises a graded index be utilized with other types of lasers that are Q- glass rod 76, a slit 80 in its associated plane 83, a switched by a rotating prism where accurate pinhole 82, an LED source 85 and a photodetector timing of the gain medium excitation with the so 86. Graded index rod 76 (such as a Selfoc fiber rotating prism is required. An intracavity Q-switch optic rod manufactured by the Nippon Sheet prism 70 is rotatable about axis 71 by motor 72. Glass Company, Ltd., Tokyo, Japan) has a radial Rotating prism 70 angularly switches the index of refraction which is parabolic in that the resonator gain by periodically sweeping through index of refraction of the core is greatest on its alignment with mirrors 54 and 56. For each 55 optical axis and continuously decreases towards combination of laser operating conditions its periphery. As such, rod 76 has the characteris- (resonator length, gain, output, coupling, etc.), tics of a common spherical lens. The optical there is an optimum prism rotation speed. This is imaging properties are determined by rod length the angular speed with a "good" alignment time and source object location. interval on the order of the pulse build up time so Slit 80 and pinhole 82 are placed at approxi- where a single output pulse is produced. If too mate equal distances from, and on a line through, fast, the laser pulse has insufficient time to build axis of rotation 71 . The pinhole slit separation and up reducing the pulse output power. If not fast graded index rod length are chosen so that the enough, multiple output pulses are produced. rod forms an erect real image of the pinhole on Light generated in the resonator cavity formed 65 plane 83 of the slit 80. It is necessary to form an EP 0 191 856 B1 8 variation or "jitter" is an important erect rather than an inverted image because an Pulse timing in the invention and relates to inverted image of the pinhole 82 would be, due to parameter present time variation between photodetec- the involved, stationary on slit plane 83 as shot-to-shot optics 92 and optimum laser pulse rod 76 is rotated through alignment with pinhole tor trigger pulse 100. The three largest sources of pulse 82. An erect image, on the other hand, is swept 5 outputtime device 79 variations of the slit 80 in the direction of arrow 84 as rod 76 jitter of timing are across amplitude, prism rota- is rotated through alignment. It should be noted photodiode current pulse and time delays within the pulser itself. that a pair of lenses (to provide an erect image), tion speed contribution to pulse jitter of each of these can configured to form an optical relay, also may be The under 100 nanoseconds by control- utilized to accomplish the same function as rod 76; w be reduced to index rod 76 is the preferred ling the prism rotation speed to within 2%, proper however, graded electronics and pulse differ- because of its smaller size. The rear design of the pulser technique current pulse. surface of pinhole 82 is continuously illuminated entiating the photodiode output controls, the shot-to-shot time jitter LED source 85 and the illuminated pinhole With these by light about 150 nanoseconds RMS, is detected by PIN photodiode 86 on the rear 15 could be held to image within the requirement for a CO2 TEA surface of slit 80. The length of rod 76 and pinhole which is well location determine the type of image, i.e., erect or laser Q-switch. embodying the present inven- inverted, formed at slit 80. The width W of slit 80 A CO2 TEA laser constructed. The design values is the order of the image width, the tion has been preferably on 79 rod length of of the slit not being critical to the operation 20 selected for timing device are a length of approximately of the invention. It should be noted that an 3 cm, a pinhole/slit separation present width of 100 micrometers. with small emitting area can be utilized, thus 5 cm and pinhole/slit LED a of rotation for the device the need for pinhole 80 inasmuch as The optimum prism rate eliminating determined to be approximately the pinhole is only utilized to define the image size. constructed was A small image is desired for good timing accuracy. 25 7,500 rpm. of the device constructed for Since it is desired only to generate one pulse per The performance The main and power rotation of rod 76, the end for end ambiguity of rod test is excellent. pulse energy and the tail completely eliminated. is eliminated by cutting one rod end at a slight were increased 76 and aligned with that the pinhole image does not sweep With the prism held stationary angle so is switched and PIN 86 for the incorrect rod 30 mirrors 54 and 56, the laser gain across photodiode main followed illustrated by arrow 90. the pulse shape is the typical pulse orientation as duration. When Q- when the image crosses by a tail of a few microseconds In operation, pinhole of about 70 rod orientation, a pulse is switched, the output is a single pulse slit 80 for the correct of 86 which causes a logic nanoseconds pulse width. The output energy generated by photodiode rpm) to terminal 88 (Fig. 3). 35 the Q-switch laser (the prism rotating at 7,500 level pulse to be coupled for enabled logic signal at 89, was 23 millijoules compared to 38 miilijoules When the laser is by a of the terminal 88 energizes high the gain switched embodiment in which half the logic pulse at shots the discharge to energy is in the tail. The peak power for 40 voltage pulser 64, causing gas than for the TEA laser40 as described hereinabove averaged 320 kilowatts (20% higher form in CO2 standard deviation of illustrated in 2 for the electro-optic Q- 40 gain switched laser) with a and Fig. 400 and 220 switch. 25%. The high and low pulses were was about 350 The relative angular relationship between the kilowatts. The pulse timing jitter achieved with none combination, graded index rod, nanoseconds RMS which was pinhole/slit noted above. and establishes the lead of the pulse jitter control methods resonator mirrors prism switched with the prism rotation 45 Oscilloscope photographs of the gain angle which, together shown in Fig. 6. determines the trigger pulse lead time. The and Q-switched output pulses are speed, thus a CO2 TEA lead is adjusted to trigger the gas discharge The present invention provides angle of the laser output 4 microseconds before the prism alignment with laser wherein the peak power and with the nitrogen tail, the resonator mirrors. The lead angle is so small pulse is increased fast electric about 0.2°) that the angle must be so normally associated with discharge (typically eliminated. The opto-elec- established by adjustment of the pinhole/slit orien- excitation techniques, method utilized in conjunction with tation, peaking the laser output while the laser is tronic timing Q-switch avoids the complexity, fired at a convenient PRF. It also may be helpful to the rotating prism and to laser damage of adjust the angle slightly greater than needed, and fragility susceptibility Q-switches. add a variable in the electronic circuitry after the 55 electro-optic photodiode output trigger signal. The timing Claims sequence is shown in Fig. 5 where 90 is the photodiode trigger signal, 91 the variable delay for the resonator gain and 92 the high voltage pulser output pulse. Laser 1. Apparatus controlling from early-to-late pulse 60 of a pulse laser device (40) comprising: output pulses arising active medium illustrated in Fig. 5 as pulses 96, 98, 100 an envelope containing an timing are mirrors (54, 56) optically timing), 102 and 104. The output power therein and resonator (optimum of said envelope, determined experimentally to be reduced by aligned with the longitudinal axis was of said laser device (40) 1/2 for 1-1/2 microseconds early or late pulse the resonator optical axis rotating prism Q-switch (70) timing. 65 being reflected by a EP 0 191 856 B1 10 interposed between said resonator mirrors; zwischen die Resonatorspiegel gesetzt ist; means (72) for rotating said prism Q-switch (70) Mittel (72) zur Rotation des Prismen Q-Schalters whereby the resonator mirrors (54, 56) of said (70), wobei die Resonatorspiegel (54, 56) des laser (40) are angularly aligned periodically by the Lasers (40) im Winkei periodisch ausgerichtet rotating prism (70); and 5 werden durch das rotierende Prisma (70); und an optical imaging device (79) including a einem optischen Bildbauteil (79), welches einen photodetector (86), a light source (82, 85) and an Fotodetektor (86), eine Lichtquelle (82, 85) und optical guideway (76) coupled to said rotating eine optische FCihrungsbahn (76) aufweist, means (72) for optically coupling light from the welche gekoppelt ist mit der Rotationsvorrichtung light source (82, 85) to the photodetector (86) 10 (72) zur optischen Kopplung des Lichts von dem thereby generating a timed electrical pulse for Licht der Quelle (82, 85) zu dem Fotodetektor (86) energizing the laser active medium, the timing of wodurch ein zeitlich festgelegter elektrischer said electrical pulse to be such as to cause the Impuls erzeugt wird zur Anregung des laserakti- alignment of said switch (70) to occur when said ven Mediums, wobei die zeitliche Festlegung der active medium has achieved peak gain, charac- w elektrischen Impulse derart ist, das Ausrichten terized in that des Schalters (70) dann zu verursachen, wenn das the light source (82, 85) is a point light source aktive Medium eine maximale Verstarkung and the optical guideway (76) comprises a graded erreicht hat, dadurch gekennzeichnet, dalS index glass rod or a pair of lenses for forming an die Lichtquelle (82, 85) eine Punktlichtquelle ist image of the light source (82, 85) which is caused 20 und die optische Fuhrungsbahn (76) einen Glas- to sweep across the photodetector (86) by rota- rundstab mit abgestuftem Index oder ein Linsen- tion of said prism Q-switch (70), thereby produc- paar aufweist zur Bildung eines Bildes der Licht- ing said timed electrical pulse. quelle (82, 85), welche veranla(5t ist, entlang dem 2. The apparatus of claim 1 wherein said optical Fotodetektor (86) zur streichen durch Rotation des guideway is formed by a graded index fiber optic 25 Prisma Q-Schalters (70), wodurch die zeitlich fest- rod (76) coupled to said rotating means (72). gelegten elektrischen Impulse erzeugt werden. 3. The apparatus of claim 2 wherein the light 2. Die Vorrichtung nach Anspruch 1, wobei die source (82, 85) is a backlighted pinhole (82) or a optische Fuhrungsbahn geformt ist von eimem small aperture LED (85) and the image is formed optischen Faserrundstab (76) mit abgestuftem on a slit (80) positioned in front of the photodetec- 30 Index, welcher gekoppelt ist mit der Rotationsvor- tor (86). richtung (72). 4. The apparatus of claim 3 wherein the pinhole 3. Die Vorrichtung nach Anspruch 2, worin die (82) and slit locations and the length of said Lichtquelle (82, 85) ein von hinten erhelltes Nadel- graded index optical fiber rod (76) are chosen loch (82) oder eine LED (85) mit kleiner Apertur ist such that the rod forms an erect real image of the 35 und das Bild geformt ist auf einem Spalt (80), pinhole (82) on the plane (83) of the slit (80). welcher vor dem Fotodetektor (86) positioniert ist. 5. The apparatus of claim 4 wherein one end of 4. Die Vorrichtung nach Anspruch 3, worin das the graded index fiber optical rod (76) is cut at an Nadeiloeh (82) und die Anordnung des Spaltes angle such that the pinhole image enters the und die Lange des optischen Faserrundstabes photodiode (86) only once for each revolution of 40 (76) mit abgestuftem Index derart ausgewahlt said prism Q-switch (70). werden, dalS der Rundstab ein aufrechtes reales 6. The apparatus of claim 5 wherein the output Bild des Nadellochs (82) in der Ebene (83) des of said photodiode (86) is differentiated prior to Spaltes (80) formt. energizing said laser active medium. 5. Die Vorrichtung nach Anspruch 4, wobei ein 7. The apparatus of claim 1 wherein said Q- 45 Ende des optischen Faserrundstabes (76) mit switch prism (70) is placed on one end of the abgestuftem Index in einem Winkei derart abge- resonator and configured such that said resonator schnitten ist, dafS das Bild des Nadelloches nur mirrors (54, 56) can be placed adjacent to each einmal bei jeder Drehung des Prisma Q-Schalters other on the opposite end, thus providing (70) in die Fotodiode (86) eintritt. alignment stability of the laser resonator. so 6. Vorrichtung nach Anspruch 5, wobei der 8. The apparatus according to any one of the Ausgang der Fotodiode (86) differenziert wird vor preceding claims, in which said laser comprises a der Erregung des laseraktiven Mediums. C02TEA laser (40) and the Q-switch rotation 7. Vorrichtung nach Anspruch 1, wobei das Q- speed is selected to eliminate the tail. Schalterprisma (70) platziert ist an einem Ende 55 des Resonators und derart konfiguriert ist, dalS Patentanspriiche die Resonatorspiegel (54, 56) einander benach- bart auf den entgegengesetzten Enden platziert 1 . Vorrichtung zur Steuerung des Resonatorver- werden konnen und so eine stabile Ausrichtung starkers eines Pulslaserbauteils (40) mit: des Laserresonators schaffen. eine Schutzhulle mit einem aktiven Medium so 8. Die Vorrichtung nach einem der Anspriiche 1 darin und Resonatorspiegeln (54, 56) optisch aus- bis 7, in welcher der Laser einen CO2 TEA-Laser gerichtet mit der Longitudinalachse der Schutz- (40) aufweist und die Q-Schalter Rotationsge- hulle, wobei die optische Resonatorachse des schwindigkeit so ausgewahlt wird, dalS die Aus- Laserbauteils (40) reflektiert wird durch einen laufer eliminiert werden. rotierenden Prisma Q-Schalter (70), welcher 65 11 EP 0191 856 B1 12 dans Revendications 2. Appareil selon la revendication 1, lequel ledit guide optique est forme par un barreau (76) d'indice auxdits 1. Appareil de commande du gain d'un resona- de fibre optique a gradient couple teur d'un dispositif laser declenche (40) compre- moyens tournants (72). revendication 2, dans lequel nant: 3. Appareil selon la contenant un milieu actif et des la source de lumiere (82, 85) est un trou d'epingle une enveloppe DEL (85) miroirs de resonateur (54, 56) alignes optique- (82) eclaire par I'arriere ou une a petite formee une fente (80) ment avec I'axe longitudinal de ladite enveloppe, ouverture et I'image est sur du (86). I'axe optique du resonateur dudit dispositif laser placee en avant photodetecteur selon la revendication 3, dans lequel (40) etant reflechi par un interrupteur optique (70) 10 4. Appareil du trou d'epingle (82) et de la fente a prisme tournant interpose entre lesdits miroirs les positions barreau (76) fibre optique du resonateur; et la longueur dudit en de maniere des (72) destines a faire tourner ledit a gradient d'indice sont choisies que moyens reelle redressee du optique a prisme (70) afin que les le barreau forme une image interrupteur de la fente (80). miroirs du resonateur (54, 56) dudit laser (40) 15 trou d'epingle (82) sur le plan (83) revendication 4, dans lequel soient alignes angulairement periodiquement par 5. Appareil selon la barreau (76) fibre optique a le prisme tournant (70); et une extremite du a un angle tel que un dispositif optique (79) de formation d'image gradient d'indice est coupee sous n'entre dans la photo- un photodetecteur (86), une source I'image du trou d'epingle comprenant dudit de lumiere (82, 85) et un guide optique (76) couple 20 diode (86) qu'une fois par tour interrupteur auxdits tournants (72) pour coupler opti- optique a prisme (70). moyens revendication dans lequel la lumiere provenant de la source de 6. Appareil selon la 5, quement (86) est lumiere (82, 85) au photodetecteur (86) afin de le signal de sortie de ladite photodiode differentie avant I'excitation dudit milieu actif generer une impulsion electrique synchronisee I'excitation du milieu actif laser, la synchro- 25 laser. pour dans nisation de ladite impulsion electrique etant telle 7. Appareil selon la revendication 1, lequel (70) est place qu'elle I'alignement dudit interrupteur ledit prisme d'interrupteur optique provoque et est configure (70) ledit milieu actif a atteint un gain de sur une extremite du resonateur lorsque du resonateur caracterise en ce defagon que lesdits miroirs (54, 56) crete, que I'autre la de lumiere (82, 85) est une source de 30 puissent etre places adjacents I'un a sur source ainsi la stabilite de lumiere ponctuelle et le guide optique (76) com- I'extremite opposee, assurant barreau de verre a gradient d'indice ou I'alignement du resonateur du laser. prend un des revendi- deux lentilles formant une image de la source de 8. Appareil selon I'une quelconque ledit laser lumiere (82, 85) qui est amenee a effectuer un cations precedentes, dans lequel com- la vitesse de mouvement de balayage sur le photodetecteur 35 prend un laser CO2TEA (40) et est choisi de (86) une rotation dudit interrupteur optique a rotation de I'interrupteur optique par la prisme (70), afin de produire ladite impulsion fagon a eliminer queue. electrique synchronisee. 40

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