Instead of using an expensive modelocked Nd:YAG laser as the seed source, NASA Goddard Space Flight Center (Greenbelt, MD) and American University (Washington, DC) scientists used commercially available laser diodes to build a small-footprint regenerative amplifier suited for ground-based satellite laser-ranging applications.
With a goal of creating 1 mJ of 532 nm light at a 2 kHz repetition rate with pulsewidths of less than 200 ps, the setup begins with a 1064 nm narrowband laser diode driven in short-pulse mode (0.2–0.4 ns seed pulsewidths). The input enters the amplifier gain unit consisting of two Brewster-cut Nd:YAG laser slabs oriented 90º to each other to simplify optical correction and create a symmetrical thermal lens effect and each pumped with an 808 nm laser-diode array. Laser-diode temporal seeding allows pulse energy to build on successive passes through the amplifier until cavity gains and losses equalize, creating 2.1 W (82 dB gain) of 532 nm light after passing through a lithium niobate crystal. Unlike commercial amplifier systems, the laser-diode seed pulses allow the pulse shape to be customized and stay unaffected by cavity length or amplifier gain. Finally, the laser-diode-based configuration can produce adjustable pulsewidths through the addition of multiple seed diodes coupled into low-cost fiber-optic combiners. Contact Demetrios Poulios at [email protected].