We report on a shortwave infrared (SWIR; 900 nanometers [nm] to 2500 nm) hyperspectral imaging microscope (HSIM) based on a tunable laser illumination source―a capability we assembled in 2013, applied in 2014, and discuss in a 2018 paper in SPIE’s Journal of Applied Remote Sensing (JARS). The HSIM is a custom built system based on monochromatic laser illumination and an imager. It is a framing system; sample translation or mirror scanning is not required. The laser used is a Q-switched Nd:YAG, 10 Hz, 850 mJ at 1064 nm and a optical parametric oscillator tunable from 410 nm to 2550 nm with a linewidth <6.0 cm-1. The laser is projected free space to a diffuser and then to the sample. The imager is an HgCdTe-based camera with 14-bit radiometric resolution and a spectral response from 900 nm to 2500 nm. Its detector array is 320 by 256 with a pixel pitch of 30 µm. The lens used was a 25 mm focal length, f/1.4, optimized for use in the near-infrared/SWIR. The sensor may be raised or lowered to vary the spatial resolution. A custom written program was used for operation and data acquisition. The program controls the laser stepping sequentially through the wavelengths, triggers the camera, and collects a set of images at each wavelength. We discuss lessons learned in the HSIM’s construction and operation as well as in data processing. Data of a polished granite slab are shown and are compared to HSI data acquired with other laboratory sensors.
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