Design and performance evaluation of a near infrared Fourier transform spectrometer

A modular Fourier transform spectrometer for the near infrared (NIR) wavelength region was designed and built. The work was motivated by the need for a versatile, economical and a dedicated instrument for research in the area of noninvasive diagnostics. The spectrometer uses a thermo-electrically cooled InGaAs detector for maximum sensitivity and CaF2 lenses for maximum transmission in the NIR region. Great attention was put to ensure that each element was designed and/or chosen to provide maximum sensitivity in the NIR region. The first part of the paper discusses the spectrometer design procedures, which include the design of detector optics, collimating optics, interferometer optics as well as the signal processing electronics and motion control. The second part focuses on performance evaluation and quantification of errors including detector noise, digitization noise and sampling errors. For measurements of water absorption, spectral signal-to-noise ratio of similar to 50000 was demonstrated over 150cm(-1) wavenumber range. Instrument sensitivity was found to be limited by interferogram data sampling noise.