Field tests have been conducted of a broadband illuminator for active hyper-spectral imaging (HSI) using a short-wave infrared super-continuum laser (SWIR-SCL). We demonstrated irradiance comparable to the sun for two-way measurements at 1.4km distance between laser and target, and we performed change detection and ranging. The SWIR-SCL outputs 64W between 1064nm and >1800nm in a nearly diffraction-limited beam over the wavelength range, a wall-plug efficiency of 15.7%, and power fluctuations of only ± 0.2%. For the field tests, the laser was placed in a 12-story tower, and the targets were placed on an 8’ x 8’ board 1.4km away on the ground. The beam quality was verified using a SWIR camera, and the spectral-spatial quality was verified using an HSI camera. At the 64W power level we showed adequate sensitivity to measure the returning light from a beam propagated 1.4km to the target, where the beam was diffusely reflected back to the tower. We also demonstrate that active illumination permits change detection to subtract out background light and ranging to measure distance to the target.
In another set of experiments, field tests were conducted using a 5W all-fiber broadband supercontinuum (SC) laser covering the short wave infrared (SWIR) wavelength bands from ~1.55 to 2.35 mm. The SC laser is kept on a twelve story tower at the Wright Patterson Air Force Base (WPAFB) and propagated through the atmosphere to a target 1.6 km away. Beam quality of the SC laser after propagating through 1.6 km is studied using a SWIR camera and show a near diffraction limited beam. The SC laser is used as the illumination source to perform spectral reflectance measurements of various samples at 1.6 km, and the results are seen to be in good agreement with in-lab measurements using a conventional lamp source. Spectral stability measurements are performed after atmospheric propagation through 1.6km and show a relative variability of ~4-8% across the spectrum depending on the atmospheric turbulence effects. Spectral stability measurements are also performed in-lab and show a relative variability of < 0.6% across the spectrum.
“Field tests for round-trip imaging at a 1.4 km distance with change detection and ranging using a short-wave infrared super-continuum laser” (to be published in Applied Optics)