Modified spatial heterodyne Raman spectrometer for remote-sensing analysis of organics

A spatial heterodyne Raman spectrometer (SHRS) is a variant of a Michelson interferometer where the mirrors in a Michelson are replaced with stationary diffraction gratings. Instead of generating an interferogram in the time domain, as in the case of a Michelson interferometer, the SHRS interferogram is generated in the spatial domain as a superposition of two-dimensional cosinusoidal spatial fringes. The spatial interferogram is recorded by an intensified charge-coupled device (ICCD) camera, and the Raman spectrum is recovered by taking the Fourier transform of the spatial interferogram. In the modified SHRS utilized in the present work, a λ/10 mirror has replaced one of the diffraction gratings. This alteration has a few effects. First, the ICCD records a greater number of photons because photons are not lost into unused diffraction orders. Second, the spectral bandpass of the modified SHRS has been doubled allowing the measurement of Raman spectra from 100-4000 cm-1. In this work, the authors present Raman spectra of organic compounds taken at remote distances of 19 meters with this modified SHRS.