Solid-state laser oscillator with gain media in active mirror configuration

#Thermomechanical effects present a major challenge to developing a solid-state laser (SSL) for generation of high-average power (HAP) with near diffraction-limited beam quality (BQ). In particular, distortions to optical phase fronts caused by transverse temperature gradients within a SSL gain medium degrade beam quality (BQ) and render the output beam useless for many important applications. A class of SSL known as “active mirror amplifier” (AMA) has shown effective reduction of transverse temperature gradients and demonstrated generation of laser output with very good BQ. A general configuration of a laser gain medium in an active mirror (amplifier) configuration is disclosed in the prior art illustration of FIG. 1.

#The AMA was first disclosed by Almasi et al. in U.S. Pat. No. 3,631,362 (1971). In the original AMA concept, a large aperture (up to 25 cm in diameter), edge-suspended, Nd-Glass disk (or slab) is pumped by flashlamps and liquid-cooled on its back face. These devices were used in a large-scale, giant pulse laser amplifier chain (rather than a laser oscillator) operating in a low-average power mode at a very low repetition rate (typically one pulse per hour). See for example, J. Abate et al., “Active Mirror: A Large-Aperture Medium Repetition Rate Nd:Glass Amplifier,” Appl. Opt., vol. 20, no. 2, 351-361 (1981) and D. C. Brown et al., “Active-Mirror Amplifier: Progress and Prospects,” IEEE J. of Quant. Electr., vol. 17., no. 9,1755-1765 (1981).

#Brauch et al., in U.S. Pat. No. 5,553,088 (1996), discloses a variant of the AMA known as the “thin disk laser”. This device uses a diode-pumped gain medium disk with a small optical aperture, typically a few millimeters in diameter and 200-400 micrometers in thickness, soldered to a heat sink. See, for example, A. Giesen et al., “Scalable Concept For Diode-Pumped High-Power Lasers,” Appl. Phys. B vol. 58, 365-372 (1994). The prior art disclosed a laser oscillator using one or more of such disks made of Yb:YAG gain media placed in a stable resonator configuration. These devices demonstrated laser outputs approaching 1 kW average power and with a BQ around twelve times the diffraction limit. See, for example, C. Stewen et al., “1-kW CW Thin Disk Laser,” IEEE J. of Selected Topics in Quant. Electr., vol. 6, no. 4, 650-657 (July/August 2000).

#The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

#FIG. 1 shows a side view of a solid-state laser gain medium in an active mirror configuration disclosed in the prior art;

#FIG. 2a shows an AMA configuration for high-average power disclosed in the prior art;

#“Active mirror amplifier (AMA) module” refers to an assembly including at least one laser gain medium in the active mirror (amplifier) configuration (such as, for example, shown in FIG. 1), means to cool the laser gain medium, means to support the laser gain medium, and means to provide optical pump radiation into the laser gain medium. A suitable AMA module may be provided in accordance with the already noted applicant's pending application Ser. Nos. 09/505,399, 09/767,202 and 09/782,788.

#“Laser gain assembly” refers to a plurality of AMA modules arranged in an array so that a laser beam may be received, amplified and reflected successively by each module.

#“Optical aperture” is defined as: “the diameter of the objective of a telescope or other optical instrument” (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th edition, published by McGraw-Hill, Inc., ISBN 0-07-045270-9).