Measurement of Absorption-Line Profiles with a Fabry–Perot Interferometer*

Abstract
We have calculated the line profiles to be expected when a Fabry-Perot interferometer is used to measure absorption lines. We have shown that large errors may be introduced in the measurement of the integrated absorption, even when an interferometer of high finesse is used. Curves and tables are given for finding the true absorption width and the true peak absorption from the apparent values observed under different operating conditions of the emission light source and the interferometer. We show qualitatively that the distortions are partially due to the presence of nonzero wings in the instrument-bandpass function. Finally, we show a Fourier series expansion of the integral giving the transmittance of the Fabry-Perot interferometer when absorbing atoms are in the light path.

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