Efficient ErYAG Amplifier for Water Vapor DIAL

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. Fibertek proposes to develop an efficient Er:YAG amplifier for energy scaling a frequency-doubled Er:YAG single-frequency laser source. This transmitter addresses target observables from the incubation (water vapor and planetary boundary layer height), explorer (methane columns), and designated (aerosol/cloud profiles) classes identified in the 2017 ESAS Decadal survey. Our proposed innovation has the potential for scaling the energy of an 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 science capability and reliability of this laser transmitter in preparation for a future Earth Explorer class mission. Development of the proposed amplifier will enable higher fidelity water vapor DIAL measurements for both day and nighttime observations for a space-borne mission. The Er:YAG fundamental wavelength (1645 nm) and frequency-doubled harmonic wavelength (822 nm) are uniquely suited to DIAL measurements of range-resolved methane and water vapor concentrations, respectively. Our overall goal will be to meet the performance specifications in the deliverable amplifier brassboard. The following objectives are targeted in the proposed SBIR phase II program: 1. Demonstration of an Er:YAG amplifier that scales the laser output of a relevant ErYAG oscillator by a factor of 2x. Demonstrating the ability to scale the output energy of the current Er:YAG oscillator is relevant for a future space-borne mission where higher energies are required to increase the water vapor signal returns over the solar background enabling daytime observations of water vapor. 2. Build a brassboard amplifier that can be integrated with an airborne oscillator previously developed under SBIR contracts and CCRPP contract 80NSSC20C0074 to demonstrate this technology on a relevant platform. Fibertek will work with the customer to understand the amplifier packaging requirements on the brassboard. 3. Demonstrate the feasibility of this amplifier technology for a future space-based mission and collect sufficient data for system level trades for enhanced laser performance over temperature. This data will be reviewed with the customer to take into account the importance of the output energy to the science mission in determining trades between output power and overall system level efficiency.
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.