Fiber Laser Development

Q-switched Tm3+-doped fiber laser

Experiments are being performed with a high-energy Q-switched Tm3+-doped polarization maintaining silica fiber laser operating in the 2 μm regime. The laser generates pulse energies >350 μJ with 115 ns pulse duration at 20 kHz. Feedback elements used with this laser include a high reflectivity mirror, a reflection grating and a volume Bragg grating (VBG). The reflection grating allows approximately 100 nm of spectral tunability and both the reflection grating and the VBG can produce laser output with sub-nanometer spectral width. Lasers of this type are used for a variety of applications including LIDAR, atmospheric propagation, and optical countermeasures. Current applications of the Q-switched system include material machining and laser induced breakdown spectroscopy (LIBS).

The laser system itself is comprised of Tm3+-doped PM silica fiber. The fiber is water cooled in order to maintain efficiency at higher power levels. The system is pumped by with a 790 nm fiber-coupled pump diode. Intra-cavity polarization elements ensure single-polarization lasing and match the polarization to the stress rods in the PM fiber. Q-switching is accomplished using an acousto-optic modulator.