ABSTRACT
A. N. Dharamsi and A. M. Bullock; Appl. Phys. B; 63,283,1996
Theoretical and experimental results for modulation
absorption spectroscopy (with simultaneous amplitude and wavelength
modulations) are given, with particular emphasis on the effects of pressure and
modulation broadening. As expected,
such broadening effects result in a loss of resolution of nearby overlapping
lines, whether these are from one or more absorbing species. The effects of
phase-sensitive detection at harmonics greater than the commonly used second
are investigated. It is shown that when
detection is performed at higher harmonics, one is able to counter the loss of
resolution due to pressure and modulation broadening. Applications in measurements of congested spectra, and in the simultaneous measurement of more than one
specie, are discussed. Other general
characteristics of signals obtained by using higher harmonic detection are also
discussed, together with corresponding applications.
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Modulation Spectroscopy