Spaceborne 3-dimensional winds lidar and spaceborne High Spectral Resolution Lidar (HSRL) for aerosol
and clouds are among the high priority future space missions recommended by the recent National
Research Council (NRC) Decadal Review. They are expected to provide the important three dimensional
winds data and aerosol data critically needed to improve climate models and numerical weather forecasting.
HSRL and winds lidar have a common requirement for high energy solid-state lasers with output
wavelengths at 1064nm, 532nm and 355nm, which can be achieved with Nd:YAG lasers and 2nd and 3rd
harmonic generations. For direct detection winds lidar, only the 355nm output is needed. One of the key
development needs is the demonstration of laser transmitter subsystem. Top issues include power and
thermal management, lifetime, high energy UV operations, damage and contamination. Raytheon and its
partner, Fibertek, have designed and built a space-qualifiable high energy Nd:YAG laser transmitter with
funding from Raytheon Internal Research and Development (IR&D). It is intended to serve as a risk-reduction
engineering unit and a test bed for the spaceborne HRSL and direct-detection Doppler winds Lidar
missions. Close to 900 mJ/pulse at1064nm and a wall-plug efficiency of 6.5% have been achieved with our
risk reduction laser. It is currently being characterized and tested at Raytheon Space and Airborne Systems.
In this paper, we will discuss the design, build and testing results of this risk reduction high energy laser
Fiber laser pumped Er:YOS laser action near 1600 nm was achieved at room temperature. Etalons and a diffraction grating were used to generate and control broad-band laser action near the 1600 nm emission center. Efficient operation was achieved in a non-optimized laser test bed.
We demonstrate passively Q switched 2% doped Er:YAG laser operation in the eyesafe region with sub 5 nsec pulse widths using Cr<sup>2+</sup>:ZnSe as a saturable absorber. A rod geometry operating in the burst mode and a micro slab geometry operating continuously are described. The micro slab geometry generates 6nsec passively Q switched pulses with over 1.5 Watt of output power and with multi kilohertz pulse repetition rates. The lasers are resonantly pumped with a 1534nm fiber laser.
We demonstrate Er:YAG laser operation at 1617nm with 6W output power and good beam quality (M-squared = 1.5) using a Volume Bragg Grating (VBG) as a wavelength selective output coupler. The low quantum defect operation of 5% is achieved by resonant pumping with a 1534nm fiber pump laser. The thermal loads of the crystal under 1617nm laser operation, under 1645nm laser operation, and under a no lasing condition are determined.
Fiber laser pumped Er:YAG laser action at 1617 nm was achieved at room temperature. An etalon was utilized for tuning the laser to the 1617 nm line. Room temperature operation was characterized and compared with 1645 nm operation. Output power close to 3 Watts CW was demonstrated at the 1617 nm laser line.
1534 nm Fiber laser pumped Er:YAG laser action at room temperature has been demonstrated with high efficiency. CW power as high as 12 Watts was achieved at 1645 nm from Er:YAG where a single TEC controller was used for thermal management. Active EO Q-switched operation with kHz repetition rate and 27 ns pulse widths was achieved with the same laser resonator.