Design and Evaluation of a Near-Infrared Dispersive Spectrometer That Uses a He-Ne Laser for Automatic Internal Wavelength Calibration

Abstract

A diffraction-grating near-infrared spectrometer that uses a He–Ne laser for automatic internal wavelength calibration is described. The instrument uses the known location of the higher diffraction orders of the 632.8-nm laser line to perform wavelength calibration in the near-infrared region. The wavelength accuracy of the dispersive spectrometer was compared with that of a Fourier transform near-infrared spectrometer whose wavelength scale was validated by calibration with the known spectrum of ethyne. The average absolute wavelength deviation between the two spectrometers for four isolated bands of trichloromethane was found to be +0.12 nm. The average values of the wavelengths of four isolated bands of trichloromethane obtained with the two spectrometers used in this study were determined to be: 1151.62 ± 0.28 nm (3ν₁), 1410.74 ± 0.52 nm (2ν₁ + ν₄), 1692.38 ± 0.49 nm (2ν₁), and 1860.20 ± 0.16 nm (ν₁ + 2ν₄).