A Broadband Laser Illuminator for Active Hyperspectral Imaging

We have been investigating the use of supercontinuum (SC) laser technology to provide active illumination for shortwave infrared (SWIR) hyperspectral sensors in order to extend their operational window into the night and heavy overcast periods. Unlike a lamp, light from a broadband laser illuminator (BLI) can propagate long distances through the atmosphere while maintaining its spatial coherence as well as high power efficiency. BLI sources have been demonstrated covering the SWIR spectral windows from 1μm to 2.5μm. We recently tested a compact source capable of producing 64W of SC output in the 1-1.8μm spectral region with 15% wall-plug efficiency. We also demonstrated end-toend sensing with a SWIR hyperspectral camera at a distance of 1.4km on a slant path near the ground. An average signal-to-noise ratio (SNR) of 126 against sensor dark noise was achieved when the beam was spread across a few pixels on a reflective target. An operationally useful system will need the beam to be spread over tens of square meters. Achieving good SNR in this case will require higher output power, which may be achieved by combining multiple sources, as well as hyperspectral cameras (receivers) with high optical efficiency and very low-noise.