Tomographic High-Energy Laser Measurement Apparatus (THELMA) for Non-Contact HEL Beam Profiling

SARA is pleased to present to the Air Force its vision for a fully non-contact 2-D high-energy laser (HEL) beam profiler.  The “Tomographic High Energy Laser Measurement Apparatus” (THELMA) measures Rayleigh scattering of the incident HEL beam off atmospheric air, which is detected by an array of photosensors surrounding the beam.  A 2-D cross-section of the beam profile is reconstructed tomographically from an array of 1-D line measurements using back-projection methods commonly used in the medical-imaging community imaging techniques such as magnetic resonance imaging or X-ray tomography. SARA’s key enabling technology for THELMA is its Reflected Irradiance Measurement System (RIMS), where the RIMS detection device is modified to measure light levels compatible with the extremely low cross-section of Rayleigh scatter.  The proposed effort is further substantiated by SARA’s prior research and development history (non-SBIR Phase I-equivalent work) of optical baffling (for stray-light reduction), tested modifications of the RIMS tube, validation of Rayleigh scatter of an appropriate laser beam in a laboratory environment, and modeling/analysis of tomographic inversion methods applied to several modeled HEL beam test cases to verify reconstructed image resolution and accuracy meeting or exceeding the Air Force’s program requirements.  The proposed device is lightweight, readily transportable, and can be used both indoors and outdoors (in day or night conditions).  THELMA is completely non-invasive to the HEL beam, since there are no expensive custom optical beamsampling components requiring thermal management being inserted into the path of the laser.