Innovators at the NASA Langley Research Center have designed a Pulsed 2-Micron Laser Transmitter for Coherent 3-D Doppler Wind LiDAR Systems. The design produces a compact, efficient, long-lifetime laser transmitter as needed for use in space, while also having potential applications as an airborne or ground-based wind measurement tool.
The transmitter is an innovative concept and architecture based on a Tm:-Fiber laser end-pumped Ho:YAG laser transmitter. This transmitter meets the requirements for space-based coherent Doppler wind lidar while reducing the mission failure risks. A key advantage of this YAG-based transmitter technology includes the fact that the design is based on mature and low-risk space-qualified YAG host crystal. The transmitter operates at a 2096 nm wavelength using Ho:YAG, resulting in high atmospheric transmission (>99 percent), versus a transmitter operating at 2053 nm using co-doped Tm:Ho:LuLiF, which suffers limited transmission (90 percent) due to water vapor interference.
The transmitter enables wind speed measurements through cloud layer. It has the ability to measure wind speed under the cloud layer from space, an important missing data element in current weather models (about 60 percent of the Earth’s surface is covered by clouds at any instant). It also has an improved signal-to-noise ratio: the system achieves 200 pulses-per-second (pps), while current methods can only emit signals at 10 pps. Faster pulsing increases the likelihood that pulses can span clouds to gauge wind speed. It’s also compact and highly efficient: the transmitter uses a pumping frequency 10X closer to the output frequency than current methods, so much less input energy is wasted as heat.
Current systems pass only 15 percent of the input power to output signals, while this new system passes over 95 percent, decreasing power and weight. Typical applications include metrology (airborne-or ground-based or space-based wind measurement for weather forecasting) and remote sensing (coherent 3-D Dop-pler wind LiDAR from satellites).