Abstract

A new theoretical formalism based on Fourier analysis that is capable of handling both analytical and background wavelength modulated signals under a variety of experimental situations has been developed. The new formalism has several appealing features; it is not restricted to small modulation amplitudes, it is capable of correctly predicting the influence of the associated intensity modulation (so called residual amplitude modulation, RAM, signals), it can deal with wavelength dependent transmission effects (e.g. etalon effects), it provides expressions for the analytical and background signals separately, and it elucidates clearly how the associated intensity and wavelength dependent transmission combine with the analyte absorption to form the total n/-harmonic signal at the lock-in amplifier output. Experimental verifications of both analytical and background signals are presented.

© 2000 Optical Society of America