Title: Thulium-Doped Fiber Amplifier Development for Power Scaling the 2 Micron Coherent Laser Absorption Instrument for ASCENDS
Author: Mark Phillips
Orgaization: Lockheed Martin

We describe the development and testing of a 2 micron Tm:glass fiber amplifier that scales the output power of a single frequency Tm,Ho:YLF seed laser from 30mW to >5W while maintaining an absolute frequency excursion of less than 1MHz. The demonstrated fiber amplifier performance provides a path for power-scaling the coherent 2 micron sensor solution to the NASA ASCENDS mission for measuring and mapping global CO2 concentrations through measurement of integrated path differential absorption (IPDA). The 2 micron sensor solution for ASCENDS is based on column-content absorption measurement biased to the Planetary Boundary Layer through measurement in the wing of a CO2 absorption feature in the vicinity of 2051 nm. Coherent detection combined with speckle averaging offers a reduced power-aperture product compared with alternative optical depth measurement methods. This approach is currently being evaluated via airborne sensor tests by JPL, with the output power per sensor channel limited to about 100mW. Operating single frequency at the wavelength of 2051 nm with a single channel output power of 5W meets the on-orbit laser transmit power flow-down requirement for ASCENDS, assuming a 0.7m telescope aperture size and an along-orbit axis spatial resolution of 80km. The power-derated fiber amplifier is also compatible with dual channel amplification to >10 W, allowing both on-line and off-line channels of the IPDA sensor to use a single power amplifier stage.