CONFERENCE REVIEW:OSA showcases solid-state laser research

April 4, 2001
The Optical Society of America's recent Advanced Solid-State Lasers topical meeting highlighted the latest advances in this critical research area.

The Optical Society of America's annual Advanced Solid-State Lasers topical meeting provides an intimate setting for world leaders of the solid-state laser community to gather and enjoy both formal presentations and informal discussions on the latest breakthroughs in solid-state laser technology. This year's three-day conference, which was held in Seattle, WA, attracted more than 320 attendees. As always, the meeting was an international affair, with about 60% of the attendees from North America, 25% from Europe, 11% from Pacific Rim countries, with the remainder from the Middle East. The event featured an excellent program organized by conference chair Chris Marshall of Lawrence Livermore National Laboratory (LLNL; Livermore, CA) and program chair Larry Marshall of Lightbit Corp. (Stanford, CA). Keynote speakers included David Welch of SDL (San Jose, CA) and Almantas Galvanauskas of IMRA, America (Ann Arbor, MI).

The conference opened with a discussion by Gary Koop of TRW (Redondo Beach, CA) about the status of the airborne laser (ABL) program. This was followed by a series of presentations about high-power diode-pumped lasers, which started with a paper on a novel end-pumped zig-zag slab laser architecture by researchers at TRW. More than 400 W multimode and 228 W in a beam 1.35 times the diffraction limit were extracted from a Yb:YAG laser in an architecture that avoids several problems inherent in side-pumped slabs and has the potential for power scaling.

In another novel architecture for generating high brightness, researchers at Heriot-Watt University (Edinburgh, Scotland) demonstrated 121-W continuous-wave (CW) output from a planar-waveguide Nd:YAG laser. The highest laser power was reported by researchers from Germany, who produced nearly 5 kW of CW power from a Nd:YAG laser. Also of interest were discussions by researchers at Mitsubishi Electric Corp. (Amagasaki, Japan) on high-power and highly efficient lasers. They reported achieving 150 W of CW single-mode output with better than 10% electrical efficiency, and more than 500 W of quasi-CW output (M2=4) at better than 20% electrical efficiency. These highly efficient, high-brightness diode-pumped laser sources illustrate the advancements being made in industrial lasers.

Also highlighted at the meeting were lasers using materials that lase directly in the mid-infrared spectral region. Researchers at the Naval Research Labs (Washington DC) presented the first demonstration of a room-temperature, diode-pumped 4.6-µm erbium-doped KPb2Cl5 laser. Chromium-doped zinc selenide (Cr2+:ZnSe) was shown by a few research groups to be a viable material for tunable and ultrashort-pulse laser sources in the 2.1 to 2.5-µm wavelength range. In addition, a collaboration of researchers from the Photonics Institute in Vienna, the University of Pisa, and LLNL demonstrated modelocked operation of Cr2+:ZnSe. As another example, high-power operation (greater than 1 W laser-pumped and 15 mW diode-pumped)was demonstrated by researchers from Belarus and the University of Hamburg.

Other laser sources

Advances in short-pulse laser sources were highlighted in the final session of the first day, with researchers presenting their work on the generation of higher peak powers and higher repetition rates from solid-state lasers. In research out of the University of Stuttgart (Stuttgart, Germany), a diode-pumped thin-disk Yb:YAG regenerative amplifier generated 1-mJ 5-ps pulses at a repetition rate of 10 kHz. Such a source may someday find its way into future micromachining applications.

Several conference presenters also detailed recent advances in terawatt-class laser sources based on Ti:sapphire. The University of Colorado at Boulder, JILA (Boulder, CO) demonstrating an 8-W, 1-kHz, 20-fs laser as the pump source for generating soft x-ray pulses of light. The Femtosecond Technology Research Association of Japan demonstrated a highly stable terawatt laser source (5.3 W, 50 Hz, 78 fs) for a laser synchrotron x-ray source. Also of interest was research out of the Swiss Federal Institute of Technology, which described a miniature Nd:YVO4 laser with a 77-GHz repetition rate that used soliton modelocking to generate short 2.7-ps pulses. Such a laser source is of interest for a number of applications, including as communications, photonic switching, and laser spectroscopy.

Fiber lasers also took center stage at the conference, led by a presentation by David Welch, who discussed recent advances in solid-state laser/amplifier technologies and the impact these advances will have on future telecommunications applications. Eyesafe fiber lasers are increasing in power, with researchers from the University of Southampton (Southampton, England) demonstrating 6.7 W from an erbium-ytterbium (Er-Yb) co-doped cladding-pumped fiber laser tunable from 1533 to 1600 nm. Ultrafast pulse generation from fiber lasers and amplifiers was also highlighted. One example involved research from IMRA America, which involved the generation of 52-fs pulses using a Yb fiber amplifier. Researcher Almantas Galvanauskas discussed recent techniques that allow using fibers with core sizes beyond the single-mode limit to increase the energy and power from ultrashort pulsed fiber lasers. In a post-deadline paper, IMRA also reported obtaining compressed 380-fs pulses with energy of more than 1 mJ from a large-core Yb-doped double-clad fiber. This energy from a femtosecond all-fiber system represents an order of magnitude increase compared to prior research efforts.

On the Tuesday evening, Professor Robert L. Byer from Stanford University (Palo Alto, CA) gave an entertaining historical perspective on the advances made in solid-state laser technology during the past 40 years. It was interesting to see the evolution of this technology, from discoveries and inventions in the laboratory to commercial products. Professor Byer has started, or been connected with, numerous successful laser companies and has a unique understanding of what it takes to turn a laboratory curiosity into a real product.

Breaking the 1-W barrier

Highlights of the visible and ultraviolet (UV) laser session at the conference included discussion of the breaking of the 1-W level of visible radiation using a diode-pumped self-doubling material. Researchers at Macquarie University (Australia) described the generation of 1.1 W of CW green output from the self-doubling crystal Yb:YAB.

The UV laser presentations were dominated by researchers from Japan. Highlights included an all-solid-state CW laser producing 2.3 mW at 195 nm from Sony Corp. (Tokyo, Japan) and improved crystal quality of the increasingly important CLBO crystal, reported by the Osaka University group.

New to this years meeting was a cash prize for the best presentation by a student. The award, which is sponsored by Lightbit, will be awarded annually at the meeting. This year's winner was Justin Mansell, a graduate student in Professor Byer's group at Stanford University. Mansell presented a postdeadline paper on a new micromachined deformable mirror for compensating thermal aberrations in a laser beam.

Many technologies that have made their debut at ASSL have quickly found their way into commercial products�including single-frequency operation induced by an acousto-optic modulator, the passively modelocked SESAM, and the periodically poled lithium-niobate optical parametric oscillator, to name just a few. It also was refreshing to see financial support for the meeting from companies including Spectra Physics (Mountain View, CA), Lightbit, SDL (San Jose, CA), and Coherent Semiconductor Group (Santa Clara, CA). Other supporters of the meeting included NASA, the US Air Force Office of Scientific Research, and the US Army's Night Vision and Electronic Sensors Directorate.

Advanced Solid State Lasers 2002 will be held in Quebec City, Quebec, Canada, February 3-6. The meeting promises to be more interesting than ever, with additional focus on solid-state lasers for telecommunications and participation and tours of local research laboratories.

Mark S. Bowers

MARK S. BOWERS is principal scientist at Aculight Corporation, 11805 North Creek Parkway S., Suite 113, Bothell, WA 98011, Email: [email protected].

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