United States Patent [191 [11] Patent Number: 5,615,043 Plaessmann Et Al
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11111 11111111 111 11111 11111 11111 11111 11111 11111 11111 11111 111111 111 11111 1111 USOO5615043A United States Patent [191 [11] Patent Number: 5,615,043 Plaessmann et al. [4s] Date of Patent: Mar. 25, 1997 [54] MULTI-PASS LIGHT AMPLIFLER Trutna et al., “Multiple-pass Raman gain cell,” Applied Optics, vol. 19, 1980, pp. 301-312. 1751 Inventors: Henry Plaessmann, Los Gatos; Tidwell et al., ‘‘Scaling CW Diode-End-Pumped Nd:YAG William M. Grossman, Los Altos, both Lasers to High Average Powers,” IEEE Journal of Quantum of Calif. Electronics, vol. 28, 1992, pp. 997-1009. Baer, “Performance of Diode-Pumped Nd:YAG and [73] Assignee: Lightwave Electronics Co., Mountain Nd:YLF Lasers in a Tightly Folded Resonator Configura- View, Calif. tion,” IEEE Journal of Quantum Electronics, vol. 28, 1992, pp. 1131-1138. [21] Appl. No.: 979,576 (List continued on next page.) [22] Filed: May 7, 1993 Primary Examiner-Nelson Moskowitz [51] Int. C1.6 ........................... HOlS 3/081; HOlS 310933 Attorney, Agent, or Firm-John E Schipper; Charles S. [52] U.S. C1. ............................. 359/346; 3591347; 372195 Guenzer [58] Field of Search ..................................... 3591337, 346, 3591347; 37272, 95, 108 [571 ABSTRACT mi References Cited A multiple-pass laser amplifier that uses optical focusing between subsequent passes through a single gain medium so U.S. PATENT DOCUMENTS that a reproducibly stable beam size is achieved within the 3,748,014 711913 Belser ..................................... 3561112 gain region. A confocal resonator or White Cell resonator is 4,360,925 1111982 Brosnar et al. ........................... 372/95 provided, including two or three curvilinearly shaped mir- 4,368,986 111983 Bennett ................................... 3561445 rors facing each other along a resonator axis and an optical 4,422,046 1211983 Munrola et al. ........................ 3591346 gain medium positioned on the resonator axis between the 4,785,459 1111988 Baer .......................................... 372/75 mirrors (confocal resonator) or adjacent to one of the mirrors 4,894,839 111990 Baer .......................................... 372193 (White Cell). In a first embodiment, two mirrors, which may 4,908,832 311990 Baer .......................................... 372175 include adjacent lenses, are configured so that a light beam 4,95 1,294 811990 Basu et al. ................................ 372/93 passing through the gain medium and incident on the first 5,103,457 411992 Wallace ..................................... 372/92 mirror is reflected by that mirror toward the second mirror 5,307,358 411994 Scheps et al. .......................... 3721108 in a direction approximately parallel to the resonator axis. A OTHER PUBLICATIONS light beam translator, such as an optical flat of transparent material, is positioned to translate this light beam by a Minelly, “Laser-diode-pumped neodymium-doped fiber controllable amount toward or away from the resonator axis laser with output power >lW,” Paper CWE6, Digest of for each pass of the light beam through the translator. The Technical Papers, Conference on Lasers and Electro-optics, optical gain medium may be solid-state, liquid or gaseous 1992, pp. 246, 247, 249. medium and may be pumped longitudinally or transversely. Coyle, “Design of a High-Gain Laser Diode-Array Pumped In a second embodiment, first and second mirrors face a ND:YAG Alternating Precessive Slab Amplifier (APT third mirror in a White Cell configuration, and the optical Amplifier),” IEEE Journal of Quantum Electronics, vol. 27, gain medium is positioned at or adjacent to one of the 1991, pp. 2327-2331. mirrors. Defocusing means and optical gain medium cooling Sandoval, “Angular multiplexing as a technique for short- means are optionally provided with either embodiment, to -pulse amplification in a high-gan xenon amplifier,” Jour- controllably defocus the light beam, to cool the optical gain nal of Applied Physics, vol. 49, 1978, pp. 5745-5749. medium and to suppress thermal lensing in the gain medium. Grossman et al., “Axisymmetric Angular Encoder for Laser Fusion,” IEEE Journal of Quantum Electronics, vol. QE-17, 1981, pp. 1870-1878. 25 Claims, 3 Drawing Sheets 1 19 20 27 5,615,043 Page 2 OTHER PUBLICATIONS Fork et al., Rev. Phys. Appl. (France), vol. 22, #12, pp. 1665-1671, Dec. 1987; abst. only supplied herewith. Streifer et al., “Phased array diode lasers,” Laser Focus/ Electro-Optics, Jun. 1984, pp. 100-109. Plaessmann et al, EEE PhotonicsTechnol. Lett., vol. 3, #lo, Fan et al., “Diode Laser-Pumped Solid-state Lasers,” ZEEE pp. 885-887, Oct. 1991, abst. only herewith. Journal of Quantum Electronics, vol. 24,1988, pp. 895-912. Gerstenberger et al, CLRO-88, vol. 7, Apr. 29, 1988, pp. Keyes et al. “Injection luminescent pumping of CaF,:U3+ 296, 298; abst. only herewith. with GaAs diode laser,” Applied Physics Letters, vol. 4, 1964, pp. 50-52. Grossman et al, IEEE J. Quant. Elec., vol. QE-17, #9, pp. Ross, “YAG Laser Operation by Semiconductor Laser 1870-1878, Sep. 1981; abst. only herewith. Pumping,” Proceedings of the ZEEE, vol. 56, 1968, pp. Khoroshilov et al., “lOkHz-Rate Amplification of 40-fs 196-197. Optical Pulses at Low Pumping Energy,” Ultrafast Phenom- Rosenkarntz, “GaAs diode-pumped Nd:YAG laser,” Jour- ena VI (Springer Verlag, Berlin, 1988), pp. 22-23. nal of Applied Physics, vol. 43, 1972, pp. 4603-4605. Georges et al., “High-efficiency multipass Ti:sapphire Kubodera et al, “Pure single-mode LiNdP,O,, solid-state amplifiers for a continuous-wave single-mode laser,” laser transmitter for 1.3-ptn fiber optic communications,” Optics Letters. vol. 16, 1991, pp. 144-146. Applied Optics. vol. 21, 1982, pp. 3466-3469. Sipes, “Highly efficient neodymium:yttrium aluminum gar- White, “Long Optical Paths of Large Aperture,” Journal of net laser end pumped by a semiconductor laser array,” the Optical Society of America, vol. 32, 1942, 285-288. Applied Physics ktters, vol. 47, 1985, pp. 74-76. Kogelnik et al., “Laser Beams and Resonators,”Proceedings Fork et al, Opt. Lett., vol. 14, #19, pp. 1068-1070, Oct. 1, of the IEEE, vol. 54, 1966, pp. 1312-1329. 1989; abst only herewith. Beeker et al, Opt. Lett., vol. 16, #26, pp. 1847-1849, Dec. Fork et al., “Multipass optical amplifier using a double confocal resonator geometry,” Revue Physique Applique, 1,1991; abst. only herewith. VO~.22, 1987, pp. 1665-1771. Plaessmann et al, Opt. Lett., vol. 18, #17, pp. 1420-1422, Sep. 1,1993; abst only herewith. Plaessman et al., “Reducing Puilse Durations in Diode Olson et al, IEEE Photonics Technol. Lett., vol. 6, #5, pp. Pumped Qswitched Solid-state Lasers,” IEEE Photonics 605-608, May 1994: abst only herewith. Technology Letters, vol. 3, 1991, pp. 885-887. U.S. Patent Mar. 25, 1997 Sheet 1 of 3 5,615,043 123 104T \ .I10 130 FIG. 1 (PRIOR ART) 1 FIG. 2 U.S. Patent Mar. 25,1997 Sheet 2 of 3 5,615,043 29a 31c FIG. 2A 1 302 303 25 FIG. 3 U.S. Patent Mar. 25, 1997 Sheet 3 of 3 5,615,043 r25 FIG. 4 51 0 M3 FIG. 5 61 0 M3 615 6i6 FIG. 6 5,615,043 1 2 MULTI-PASS LIGHT AMPLIFIER power applications because the fiber may damage, and it is difficult to pump single-transverse-mode fiber with high FIELD OF THE INVENTION power diodes that are not themselves single transverse mode. See J. D. Minelly et al, “Laser diode-pumped neody- The invention relates generally to lasers and more par- 5 mium-doped fiber laser with output power >1 W,paper ticularly to amplification of optical power by laser gain CWE6, Conference on Lasers and Electro-optics, 1992, media. This work was performed under NASA Contract No. Digest of Technical Papers, Opt. SOCof America, Washing- NAS 7-1 145. The U.S. Government has certain fights in this ton, D.C., for a particular approach to this problem. The invention. second category of amplifier is single- or double-pass ampli- fiers where for efficiency the input must be energetic enough BACKGROUND OF THE INVENTION lo to saturate the amplifier. These amplifiers in the master oscillator/power amplifier configuration are technologically Lasers and laser amplifiers can be energized by many very important. However, these lasers are not generally different means and may use many different laser media. Of optimized for large gain, but rather for high power, high special interest here are laser amplifiers energized or energy, and high extraction efficiency. One example of an “pumped” by laser diodes. For a review of laser diode l5 amplifier that does not fall directly into the two broad pumped solid-state lasers see T. Y. Fan and R. L. Byer, categories above is the tightly folded amplifier or resonator “Diode laser-pumped solid-state lasers”, I.E.E.E. Jour. of disclosed by T. M. Baer in U.S. Pat. Nos. 4,785,459, Quant. Elec., vol. 24 (1988) pp. 895-912. Here the term 4,894,839 and 4,908,832. Another example is a precessing “solid-state lasers” includes all lasers, except semiconductor slab amplifier discussed by D. B. Coyle, “Design of a high laser diodes (referred to as “laser diodes”), in which the laser 2o gain laser diode array-pumped Nd:YAG alternating preces- gain medium is a solid-state material. Original work in laser sive slab amplifier”, I.E.E.E. Jour. Quant Elec., vol. 27 diodes, and a laser diode’s applicability to pumping of (1991) pp. 2327-2331. solid-state lasers, is discussed by W. Streifer et al, “Phased R. P. Sandoval, in “Angular multiplexing as a technique array diode lasers”, Laser FocuslElectro-optics, Jun. 1984, for short-pulse amplification in a high gain xenon amplifier”, PP. 100-109, by R. J. Keys and T. M. QuiSt, “Injection 25 Jour. Appl. Phys., vol. 49 (1978) pp. 5745-5749, notes that luminescent Pumping of C@2:U3+with diode lasers’’, passing a sequence of light beams through the same volume APPl.