CTI has demonstrated Q-switched pulse amplification in Tm,Ho:YLF at >400 mJ output pulse energy for 60 mJ of input energy using a single stage 2-pass (on-axis) amplifier. The pulse duration was 800 ns. A double-pass gain of 10 was demonstrated for 35 mJ input pulse energy. The optical-to-optical efficiency for the 2-pass amplifier was 8%. This is the first demonstration of multiple hundred millijoule output and >10 times double-pass amplification in an all conduction-cooled two micron laser pump module: both the laser rod, operating at 200 K, and the pump laser diodes, operating at 300 K, are conduction-cooled to embedded cold-plates that remove heat from the pump module. As such, this design is directly compatible with the use of heatpipe and space radiator technology for thermal management in a space environment.
Pulsed coherent Doppler lidar systems have matured rapidly, especially at solid-state wavelengths. Turnkey systems are commercially available and are being deployed for various aviation applications. Doppler lidar data is used in the airport terminal area to map hazardous wind shear and turbulence levels and to detect and track wake vortices. Future applications could include slant path visibility monitoring. Several permanent installations and rapidly deployable instrument configurations have been achieved. The benefit of the infrared Doppler lidar relative to its microwave counterparts is the ability to sense clear air hazards, especially those in and around local terrain features. The fact that the lidar beam is quite narrow eliminates artifacts associated with sidelobe-induced ground clutter. This paper summarizes our autonomous pulsed lidar developments and reviews sample results.
This paper discusses the design and development of a 2J, 10Hz coherent Doppler wind lidar transmitter for global wind sensing from the International Space Station. This work is being performed in support of a proposal to operate such a lidar from the Japanese Experimental Module. The conceptual lidar transmitter design is complete and risk reduction measurements are currently underway to demonstrate the 2J, 10Hz operation using a 2 micron laser transmitter with a MOPA (master oscillator – power amplifier) configuration. The paper discusses the lidar performance requirements for global wind sensing from the Space Station, general design characteristics of the two micron lidar transmitter, and the current status of the risk reduction measurements.
This paper discusses the design and current development status of the coherent lidar transceiver being developed by Coherent Technologies Inc for the NASA program, SPARCLE (SPAce Readiness Coherent Lidar Experiment). SPARCLE is intended as a precursor mission to a fully operational satellite system, measuring global wind profiles from the Space Shuttle, with a planned launch date in March 2001.
Global wind measurement is a key component of weather prediction. Coherent wind lidar provides excellent wind profile measurement sensitivity and accuracy through the use of heterodyne detection technique. A high pulse energy, high beam quality, very narrow linewidth laser is essential for successful coherent wind detection. We have developed an eye- safe all solid state Ho:Tm:YLF power oscillator with ring configuration to be used as coherent lidar transmitter. It achieved an optical to optical efficiency of 0.03. A Q- switched output energy as high as 109 mJ at 6 Hz, with a pulse width of 170 ns is obtained. The resonator alignment sensitivity, heat dissipation efficiency and polarization extinction ratio are all characterized for space application lidar. Laser performance as a function of laser rod temperature and pump intensity has also been investigated. The high power and high beam quality of this laser make it well suited for use as a coherent wind lidar transmitter on a space platform.
Pulsed coherent solid-state 2 micron laser radar systems have been developed at Coherent Technologies, Inc. for ground- and airborne-based applications. Ground-based measurements of wind profiles and aerosol backscatter have been performed for several years. Examples of wind and aerosol backscatter coefficient measurements will be presented which cover a variety of weather conditions. Airborne measurements of wind profiles below the aircraft have been performed by Wright Laboratories, operating in a VAD measurement mode and will be reviewed. An engineered flight-worthy coherent lidar system is under development at CTI for flight on the SR-71 aircraft, in support of the High Speed Civil Transport program. Flights will be conducted by NASA-Dryden Flight Research Center at altitudes above 60,000 feet for the measurement of atmospheric turbulence ahead of the aircraft. Efforts are also underway at CTI for the development of high power coherent laser radar systems. Extensive detailed physical optics models of diode-pumped solid-state laser performance have been developed to characterize transient thermo-optic aberrations and the overall efficiency of lasers intended for space-based applications. We are currently developing a 2 micron 0.5 J/pulse transmitter with a 10 Hz PRF and a pulse duration of 400 - 500 ns. The status and expected space-based wind measuring performance for this system will be presented.