ABSTRACT
A. N. Dharamsi; J. Phys. D 28, 540, 1996
A theoretical
treatment of modulation absorption spectroscopy, applicable when amplitude and
frequency modulation are present simultaneously, is given. The effects of any relative phase difference
between these two types of modulation are incorporated, and the theory is
applicable to an experiment involving detection at any harmonic order of the
modulation frequency. The results
obtained are given in terms of the derivatives of the absorption lineshape
function and bring out the connection to Nth order derivative spectroscopy
naturally. General expressions for any
gaseous molecular absorption line are given. It is shown that there are certain advantages that are obtained when one
performs higher harmonic detection, including an increase in the wavelength
resolution. Experimental results are
obtained and compared with the predictions of the theory developed
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Modulation Spectroscopy