Emission spectra studies by means of Fourier transform spectroscopy in the visible range

A new Fourier spectrometer has been constructed for use in the visible range, where the noise is due to the signal itself. With this instrument it is possible to record in one sweep a spectral range of 10 000 cm-1. The interferograms contain 106 points (corresponding to a resolving power of about 106) and the reproducibility of the measurements of the wavenumbers of recorded lines in emission spectroscopy is 10-7 in relative value; the accuracy of the measurements of the position of the lines, is proportional to line intensity, and is of the order of a few hundreths of mK (1 mK = 10-3 cm-1) for the strongest among them. Finally, the intensity of the weakest measurable line is one thousandth of the intensity of the strongest line of the spectrum. Compared to a conventional grating spectrometer, the Fourier transform spectroscopy has the advantage among others, of maintaining the throughput gain (Jacquinot) constant for all the lines of the spectrum; the multiplex gain (Fellgett) does not disappear entirely; it depends strongly on the intensity of the lines. The work presented here, proves clearly that the extension of Fourier transform spectroscopy to regions where the noise is principally photon-noise, is effectively possible.