A demonstration of spatial heterodyne spectrometers for remote LIBS, Raman spectroscopy, and 1D imaging

Abstract

Three spatial heterodyne Raman spectrometers, one free standing, the others monolithic, have been used for remote Raman and LIBS for samples at a distance of 4.5 m and 1D Raman imaging. The wide area measurement capability of the SHS was demonstrated and shown to reduce sample photodegradation in the case of Raman, using large laser spots on the sample, without loss of signal or decreased spectral resolution. 1D Raman imaging using a free standing SHRS and a monolithic SHRS was demonstrated and shown to provide better signal-to-noise ratio (SNR) spectra for heterogenous samples than spectra measured without imaging. Improved SNR using 1D imaging is the result of spatial separation of the signal from different areas of the sample, which reduces the contribution of shot noise from stronger scattering sample regions to more weakly scattering adjacent sample regions. For 1D imaging of adjacent samples, within the field-of-view (FOV) of the spectrometer, the SNR improved up to four times, with no loss of spectral resolution or spectral range, and a spatial resolution of 280 μm was demonstrated for samples located at 4.5 m from the spectrometer.