Multichannel Fourier transform Raman spectroscopy: Combining the advantages of CCDs with interferometry

A common-path (Sagnac) interferometer combined with a charge-coupled device (CCD) was evaluated for Raman spectroscopy in the near-infrared region. A spatial interferogram of the scattered light was projected onto the face of the CCD, and a Fourier transform of the intensity vs. pixel data yielded a Raman spectrum. This multichannel Fourier transform (MCFT) technique retains several advantages of FT spectroscopy, including high throughput, excellent frequency precision, and wide spectral coverage, while also retaining the multichannel, shot-noise-limited operation of the CCD. The signal-to-noise ratio (SNR) for the MCFT system was comparable to that for a dispersive spectrometer for the same laser power and integration time, and its frequency and intensity stability were excellent. Resolution is dictated by the number of CCD pixels, and was 25 cm(-1) for the initial MCFT system. In addition to stability, a possibly important feature of the MCFT spectrometer is its large A Omega product (etendue), which results in a signal which is independent of laser beam diameter over the range of 60 mu m to 1.3 mm.