Differential absorption lidar demands high-power, narrowband DBR sources

Water vapor plays a role in many atmospheric processes and is a primary driver of weather. Atmospheric water-vapor concentrations span more than four orders of magnitude from the planetary boundary layer—where high-impact weather initiates—to lower levels in the upper troposphere and lower stratosphere, where water vapor has significant and long-term impacts on the Earth’s radiation budget. NASA Langley has been fielding airborne water-vapor differential-absorption lidar (DIAL) systems for more than 30 years in support of atmospheric chemistry, high-impact weather, and climate process studies, with an end goal of implementing a water-vapor DIAL system in space for weather and climate applications. In collaboration with the National Center for Atmospheric Research (NCAR) and Montana State University, NASA researchers are also working towards implementing a nationwide water-vapor-profiling network to improve weather forecasting and climate modeling with an automated,eye-safe, lowcost, and compact ground-based watervapor DIAL system. NASA recognizes that the airborne-, space-,and groundbased water-vapor DIAL systems share a common requirement for frequency-agile, narrowband, rugged seed lasers that are used to injection- seed higher-power pulsed lasers. A differential-absorption lidar (DIAL) system (inset) has been developed by NASA using Photodigm distributed Bragg reflection (DBR) injection-seed lasers.