Fiber Optics for Remote Delivery of High Power Pulsed Laser Beams

The work described here is focused on the technology to enable remote fiber optic delivery of high-power, pulsed laser beams for diagnostics used in combustion and flow-field characterization. Fiber delivery is desirable since it is not always practical to locate laser diagnostic equipment in close proximity to the harsh environment associated with propulsion test facilities (e.g., jet or rocket engine testing). In this study both onedimensional hollow core waveguides and photonic bandgap fibers were investigated. Relatively large bore (~ 1000 µm) hollow waveguides were found to be the optimal fiber solution for their ability to deliver relatively high peak power pulses (5 ns duration at energies > 10 mJ/pulse) with an acceptable beam quality (M 2 ~ 10 to 20). Using such waveguides, a Coherent Anti-Stokes Raman Spectroscopy (CARS) system with fiber delivery of the laser beams was fully demonstrated in laboratory experiments. The technology is currently being applied to a field-ready CARS system, which will be initially demonstrated by mapping the temperature of exhaust products in a jet engine plume.