MOPA Laser Transmitter with Passive Q-Switch for Space LIDAR

The use of a Passive Q-Switch (PQS) in a high power MOPA configuration with multiple tens of watts output will enable a smaller, compact, lightweight lidar transmitter with significantly increased reliability over existing legacy transmitters for space applications. The proposed MOPA transmitter will reduce transmitter size and weight by integrating a Passive Q-switch (PQS) into the master oscillator, which will eliminate the Active Q-switch (AQS) used in high power MOPA’s. Replacing the AQS with a PQS eliminates the high voltage power supply, high voltage AQS driver, and intracavity AQS crystal. This also eliminates the sensitive alignment and locking of the intracavity AQS and mount. Cr:YAG PQS crystals have been used as a separate component in a resonator to produce Nd:YAG and Nd:YVO4 PQS lasers.They can be designed to produce longer output pulse widths around 8-10 nsec and use QCW laser diode pumping to fix the laser rep rate. The MO output can be amplified up to the level required for lidar applications. The proposed transmitter will use a Carbon Fiber (CF) optical bench to reduce weight and increase stiffness in an aluminum housing. The resonator, amplifiers and second harmonic generation optics and mounts will occupy the top side of the optical bench, with the beam expander located on the bottom side. Two amplifiers will be used with the MO to amplify the energy per pulse up to 5-10 mJ at 4.0-5.0 kHz rep rate, depending on application requirements. The MOPA output can be configured with SHG, THG and OPO wavelength conversion options to operate from the UV to IR. For environmental monitoring applications the laser will operate at 1064 nm and 532 nm. We propose the engineering model phase II deliverable laser to be configured with 6 mJ total output energy/pulse at 4 kHz rep rate, with 3 mJ at 1064 nm, and 3 mJ at 532 nm, and a proposed rep rate of 4 kHz and pulse width of 10 nsec. The laser will use Nd:YVO4 laser slabs pumped at 878.6 nm with VBG stabilization.

This effort proposes miniaturization and reliability over existing lidar transmitter configurations for use SmallSats including environmental research and monitoring. The proposed transmitter applications include Earth Sciences lidar systems, such as use in Cloud Physics Lidar systems based at NASA Goddard Space Flight Center at code 610 (Dr. Matthew McGill). The transmitter would enable smaller, lighter, more reliable lidar instruments for space-based systems, particularly in SmallSats where lidar system weight and volume must be minimized.

Applications include military lidar for ranging and imaging, particularly with the emerging use of UAV military platforms, and military space based lidar in SmallSats for surveillance and other military applications. Lidar systems are also used on UAV’s for commercial applications. Lidar can also be used in underwater imaging in UUV's at 532 nm wavelength for bathymetry and object detection.

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