CONFERENCE REVIEW

CONFERENCE REVIEW

Solid-state laser research focuses on practicality

ORLANDO, FL--Recent advances in the development of new solid-state lasers and nonlinear-frequency-conversion tech niques were the subject of the 12th Advanced Solid State Laser Topical Meeting, held January 27-29, 1997, at the Grosvenor Resort at Walt Disney World Village. During the three-day Optical Society of America sponsored meeting, plenary sessions covering potential solid-state laser applications in projection video, bioanalysis, photo lithography, and defense were combined with technical and poster sessions describing advances in solid-state materials and devices.

Although a ga¥still exists between current technology and the applications described at the conference, significant progress has taken place in the development of high-power, diode-pumped infrared lasers and optical parametric oscillators (OPOs). In addition, research results on new gain media and nonlinear crystals capable of producing UV light in the 200- to 300-nm range were reported.

Progress in the development of OPOs has been accelerated by the availability of periodically poled lithium niobate (PIPLIN) with domain spacings suitable for pumping at visible and near-infrared wavelengths. Although optical damage problems still exist at visible wavelengths, the combination of high nonlinearity, low loss, and custom phase-matching properties makes this material highly attractive.

In a postdeadline paper, R. Batchko, M. Fejer, and coworkers from Stanford University (Stanford, CA) described a 532-nm-pumped PIPLIN OPO that could be tuned continuously in two bands (953 to 1000 nm and 1160 to 1234 nm). In the same session, low-threshold operation of a pump-resonant, 3-µm OPO was reported by a grou¥from Aerospace Corp. (Los Angeles, CA). This device, pumped by the 1064-nm output of a diode-pumped Nd:YAG laser, had a threshold power of 350 mW and a maximum single-frequency, 3.2-µm output power of 320 mW. During the regular session, initial results on the performance of large-aperture, diffusion-bonded stacks of PIPLIN were reported by Larry Myers of Wright Laboratories (Wright Patterson Air Force Base, Dayton, OH), and a novel, six-wavelength pulsed PIPLIN OPO was described by David Matthews of Light Solutions (Mountain View, CA).

Pulsed OPOs

Several papers describing the operation of pulsed OPOs based on conventionally phased-matched materials were also presented. Allik and coworkers from the Night Vision Laboratory (Ft. Belvoir, VA) described the operating characteristics of a silver gallium selenide OPO pumped at 1.5 µm. At a pum¥power of 10 mJ, output energies of 50 to 500 µJ were observed as the output wavelength was decreased from 13 to 7 µm. A grou¥from Lockheed Sanders (Nashua, NH) reported on 2-µm-pumped parametric amplifiers and oscillators based on zinc germanium phosphide. An average 4.1-µm output power of 5.2 W was obtained from a doubly resonant OPO with a conversion efficiency of 41%.

Reflecting progress in diode-laser technology and the development of gain crystals for laser pumping, several papers described high-power, diode-pumped solid-state lasers operating in the near- and mid-infrared. Groups from Lawrence Livermore National Lab oratory (Livermore, CA) reported on high-power operation of Er:YAG, Tm:YAG, and Yb:YAG. Camille Bibeau and Ray Beach described a Yb:YAG laser pumped by an array of 940-nm diodes that had a CW 1030-nm output power of 115 W and an average Q-switched output of 100 W. The Q-switched results were obtained at a repetition rate of 6.25 kH¥and a pulsewidth of 60 ns. Eric Honea and coworkers described a CW 2-µm Tm:YAG laser with an output power of 115 W. The 360 W of delivered pum¥power for this end-pumped laser was generated by 805-nm diodes. Ralph Page and coworkers also reported greater than 1 W of 2.94-µm output under pulsed-pumping conditions from a novel, diffusion-bonded slab laser design.

High-power 1064-nm Nd:YAG results were reported by Schone and coworkers from Zentrum Hannover e.V. (Germany). They obtained more than 750 W from a 6-mm-diameter rod pumped by fiber-coupled diodes (see figure).

Interest in the development of UV lasers for lithography and remote sensing of biological molecules was reflected in papers describing research studies of cesium-doped lithium triborate (CLBO) and cerium-doped fluorides. From a nonlinear optical device standpoint, CLBO appears to be superior to water-soluble crystals and to beta-barium borate (BBO), but it is clear that a number of materials issues must still be addressed. J. Pinto and L. Esterowit¥ of the Naval Research Laboratory (Washington, DC) described a difference-frequency laser in which the fourth harmonic of a Nd:YAG laser was used to pum¥a Ce:LiCAF crystal. Tunable output was generated by summing the fundamental 1064-nm radiation with the frequency-agile output of the Ce:LiCAF laser in a BBO nonlinear crystal. Output energies as high as 100 µW were obtained near 228 nm in this experiment.

Taken as a snapshot of the solid-state community as a whole, the conference indicates an increasing focus on the practical issues associated with solid-state laser development. Hopefully, this shift to more development and less research will result in the introduction of new lasers for both the commercial and defense communities.

G. J. Dixon

G. J. DIXON is assistant professor of electrical engineering, Center for Research and Education in Optics and Lasers, University of Central Florida, Orlando, FL 32816.