Princeton Claims Laser Breakthroughs

CRANBURY, N.J. -- Princeton Lightwave Inc. (PLI), a producer of near-infrared high-power diode lasers and application specific detectors for communications, defense, and sensing applications, announced two breakthrough results involving (i) the development of record high-power 1530 nm diode laser bars as well as (ii) the first prototype of eye-safe 1.6 um Er:YAG solid state lasers (SSLs) with resonant, ultra-low photon defect pumping at 1530 nm. These results have been achieved as part of an R&D contract supported by the Department of Defense’s High Energy Laser Joint Technology Office. The goal of this BAA contract, started in June 2004, is the development of highly scalable eye-safe solid state lasers with InP-based ultra-low photon defect diode pumping. PLI has partnered with scientists at the Army Research Laboratory in Adelphi, MD as collaborators for this research.

In support of this SSL development program, PLI has demonstrated world record powers of 44 W in continuous wave (CW) operation and 80 W in quasi-CW (QCW) operation for single 1-cm long 1530 nm laser diode arrays. Additionally, two-dimensional stacks of 10 arrays with microlens collimators have yielded powers exceeding 300 W CW output at 1530 nm. The energy brightness for these uniquely lensed 2-D stacks reaches 1 W/ cm2 (mRad)2 = 80 kW/cm2 Sr.

Resonant pumping of Er:YAG SSLs with InP-based 1530 nm diode lasers has been demonstrated using single-mode fibered pump modules as well as using 3-array mini-stacks. The significance of this SSL pumping scheme lies in the very small difference between pump photon energy and output photon energy: due to this very small “photon defect,” minimal energy dissipation in the SSL gain medium should yield superior beam quality and the potential for scaling to architectures capable of multi-kW eye-safe output powers.

Initial results using single mode pump modules demonstrated threshold powers as low as 80 mW with FBG-assisted pump spectrum narrowing and allowed PLI scientists to reveal fundamental features of resonant diode pumping and the fluorescence dynamics of the Er:YAG gain medium. Details of these results have been accepted for publication in Applied Physics Letters. The use of 1530 nm single mode pump lasers in miniature Er:YAG SSLs promises to provide high-efficiency sources for eye-safe laser designation and ranging (ladar) applications.

Following the experiments with low-power single mode pumps, a first prototype of a high-power SSL with resonant 1530 nm diode array pumping was assembled using a high brightness, lensed mini-stack of 3 diode arrays pumping a 3 cm long, 2 mm diameter Er:YAG rod. The low divergence of the pumping beam allowed for the use of external mirrors, avoiding the lens duct approach. An initial peak power of 3 W in QCW regime has been achieved without heat sinking of the Er:YAG rod, and further experiments will lead to increased peak power and CW operation. In later stages of this program, PLI’s two-dimensional pump laser stacks will be instrumental in realizing greatly increased resonantly pumped SSL output power.

“We believe that the results achieved so far in this program are paving the way for the development of a new generation of eye-safe solid-state lasers with resonance diode laser pumping,” says Dmitri Garbuzov, PLI’s Chief Scientist and Principal Investigator for the program. “This record low photon defect 1530 nm pumping should provide extremely high beam quality at high-power operation for next generation diode-pumped solid state lasers, and PLI’s accomplishments on 1530 nm high-power laser diode arrays will be a critical factor in DPSSL beam quality optimization at maximum output power.”

Princeton Lightwave Inc. (PLI)