engleski

Investigation of single-factor calibration of the wave-number scale in Fourier-transform spectroscopy

Abstract: In the ultraviolet and visible regions, a principal advantage of Fourier Transform Spectroscopy (FTS) is its potential to produce spectra with high resolution, high wavelength accuracy, and simultaneous coverage of a large spectral range using an instrument of modest size. We have used the fundamental and frequency-doubled output of a single-frequency tunable laser locked to a precisely known transition in molecular iodine to provide simultaneous calibration of the FTS in the visible and near ultraviolet regions and to investigate the limiting uncertainty involved in calibrating spectra by using a constant multiplicative correction to the optical frequency scale. An integrating sphere was used to introduce the laser light as a pseudoincoherent source and provide a uniform illumination of the FTS entrance aperture. The sphere also served to combine the laser beams with light from a series of mercury electrodeless discharge lamps containing argon carrier gas at selected pressures. Four strong lines in the spectrum of 198Hg were measured with these lamps to obtain precise wavelengths and argon pressure shift coefficients. These lines, emitted from lamps with argon pressures in the range 33 Pa (0.25 Torr) to 1330 Pa (10 Torr), are suitable for future calibration of the FTS without need for the laser source.

Fourier Transform Spectrometer; Metrology; Mercury atomic lines; Wavelengths

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