SBIR-STTR Award

Fibertek proposes to develop technology for power scaling a frequency doubled Er:YAG single frequency laser source to meet the needs for a planned water vapor DIAL space-based instrument. Our approach will focus on quantifying the system level benefits of reduced-temperature operation of a power-scaled Er:YAG oscillator and power amplifier. A primary challenge to the Er:YAG laser system is inherently low gain and quasi-three-level lasing transitions of the erbium activator ions. It is well-established that reducing the laser gain medium to sub-ambient temperatures improves achievable laser efficiency. However, models based on cross-section data from the current literature that simply use Boltzman statistics for scaling cannot account for the observed improvements, inhibiting system trades of performance versus temperature. Fibertek proposes to address the lack of data in the current literature by collecting spectroscopic data over the temperature range 77K-300K to determine the optimum gain medium temperature for Er:YAG. This data will be integrated into an advanced energetics model to accurately predict improvements in laser efficiency. The model predictions will be validated through laser demonstrations as well as to guide a study to assess the improvements relative to potential SWaP penalties associated with operating at a reduced temperature. Energy scaling of Er:YAG could potentially provide NASA with a compact laser transmitter that could revolutionize weather and climate research by providing three dimensional distributions of water vapor profiles, estimates of perceptible water vapor, high resolution methane column measurements, distributions of planetary boundary layer heights, and attenuated profiles of aerosols and clouds. Potential NASA Applications (Limit 1500 characters, approximately 150 words): The key NASA application include the following all of which have been identified as mission and technology development area in the 2018 Earth Science Decadal Survey. An Er:YAG MOPA could provide a higher energy, more efficient, more robust and lighter weight approach for Water Vapor and Methane Differential Absorption Lidar systems Coherent detection 3-D wind measurement systems Potential Non-NASA Applications (Limit 1500 characters, approximately 150 words): DoD: Lidar systems and illuminators require high pulse energy for greater range and wider field of view, with a requirement for operation in the eyesafe window (1400-1700nm). Er:YAG at 1645nm is well suited for these applications. Commercial: An Er:YAG laser with higher pulse energy can extend range for current wind lidar systems for wind farm and other types of commercial wind measurements. Duration: 6

Fibertek proposes to develop the technology for energy scaling a frequency-doubled single-frequency Er:YAG laser source with a fundamental wavelength of 1645nm and a frequency doubled wavelength of 822nm. This proposed work will provide an enabling technology for a space-based water vapor/methane DIAL instrument with the potential for scaling the energy of the Er:YAG water vapor DIAL transmitter by a factor of two compared to the current state-of-the-art system being developed under the ABLE IIP, further enhancing the transmitter capability by enabling day-time observations of water vapor. The proposed program will focus on developing a cryo-cooled laser amplifier to meet the performance needs of a space-based frequency-doubled single-frequency Er:YAG laser for a water vapor DIAL instrument. The phase I program focused on collecting temperature dependent spectroscopic data on Er:YAG to support development of an efficient amplifier design. The proposed phase II work outlines a systematic approach to optimizing the amplifier performance through parametric breadboard experiments studying the effect of doping concentrations, crystal lengths and temperature on amplifier performance. Data collected from the breadboard will enable a trade study of devices for space-based compatible cryo-cooling and identifying the most efficient system level approach for an Er:YAG laser amplifier. A deliverable Er:YAG amplifier and frequency converter module will be designed and built that will be compatible with amplifying previously built single-frequency Er:YAG laser sources developed under SBIR funding. Anticipated

Benefits:
The proposed work aligns with a current IIP program investigating a water vapor/methane DIAL space-based instrument. This instrument targets observables in the incubation (water vapor and planetary boundary layer height) and explorer (methane columns) classes identified in the 2017 ESAS decadal survey. An Er:YAG amplifier provides a path to scaling the laser energy which is enabling for daytime observations of water vapor. An energy scaled 1.65 Er:YAG system also provides a cross cutting application for high rep-rate 3D wind lidar. The proposed amplifier has applications for scaling 1.65µm lasers for use as illuminators and long range lidar systems for the DOD, where requirements on eye safety dictate a need for wavelengths in the 1400nm to 1700nm band. An Er:YAG amplifier at 1.65µm is ideally suited to scaling power for these applications that increasingly require higher power for greater range and sensitivity.