A novel method of calculation-separating second order spectrum in grating spectrometers

In grating spectrometers, according to wavelength, short-wave second-order spectrum superimposes on long-wave spectrum with the wavelength twice as long as the short-wave. Usually spectrum of long-wave range is got via preventing the superimposition of short-wave second-order spectrum by cut-off filters. This paper analyses the characteristic of the ratio of short-wave second-order spectrum in long-wave superimposing spectral range to first-order spectrum in short-wave free spectral range of diffraction gratings. The paper studies a novel method of obtaining long-wave spectrum via calculation-separating short-wave second-order spectrum from mixed spectra in long-wave superimposing spectral range by data processing with the spectrum of free spectral range and the ratio (instrumental parameter) of short-wave second-order spectrum to first-order spectrum measured beforehand. Spectrum-measurement experiments were carried out by VIS-NIR spectrometers (0.36 - 1.0μm). That the spectrum data got via calculation-separation coincide with those got via cut-off filter indicates that spectrum can be obtained by processing the measured date without filters in whole operating wavelength.