Frequency stabilized lasers for space applications

Abstract

Frequency stabilized narrow line-width lasers have a broad range of applications including precision metrology, spectroscopy, atomic clocks and geodesy. This technology will be a key enabler to several proposed NASA science missions. Although lasers such as Q-switched Nd-YAG are now commonly used in space, other types of lasers -especially those with narrow linewidth -are still few in number and more development is required to advance their technology readiness.In this paper we discuss a reconfigurable laser frequency stabilization testbed, and end-to-end modeling to support system development. Two important features enabling testbed flexibility are that the controller, signal processing and interfaces are hosted on a field programmable gate array (FPGA) which has spacequalified equivalent parts, and secondly, fiber optic relay of the beam paths. Given the nonlinear behavior of lasers, FPGA implementation is a key system reliability aspect allowing on-orbit retuning of the control system and initial frequency acquisition. The testbed features a dual sensor system, one based upon a high finesse resonator cavity which provides relative stability through Pound-Drever-Hall (PDH) modulation and secondly an absolute frequency reference by dither locking to an acetylene gas cell (GC). To provide for differences between ground and space implementation, we have developed an end-to-end Simulink/ Matlab ® -based control system model of the testbed components including the important noise sources. This model is in the process of being correlated to the testbed data which then can be used for trade studies, and estimation of space-based performance and sensitivities. A 1530 nm wavelength semiconductor laser is used for this initial work.

Spaceborne laser filamentation for atmospheric remote sensing

“…Substantial R&D efforts were made to space‐qualify high power lasers since the mid‐1990s . Space qualification has proven challenging and lengthy, with special efforts made for maintaining precision alignments of optical mounts during and after launch, preventing contamination of optics from out‐gassing materials in vacuum, resistance of electronic components and optical materials to vacuum, thermal cycling, and radiation exposure . Achieving good coating performance under vacuum is also challenging, with strong laser degradation for porous coatings under vacuum exposure .…”