Concentration-modulated absorption spectroscopy. Part 4. - The use of continuous-wave lasers

The concentration-modulation approach to the study of absorption spectra of atoms and molecules developed with mode-locked dye lasers is extended in this paper to continuous-wave lasers. A 'gain' theory is developed for use with c.w. lasers and a comparison is made between the 'gain' measurements of our c.w. experiments and those of earlier studies using pulsed lasers. The experimental agreement between the measured c.w. 'gain' and the pulsed 'gain', after correcting for differences between the experimental arrangements employed, provides strong support for the 'gain' theory developed here. It is clearly seen that by means of this theory and the derived equations it will be possible to evaluate species concentrations where the state lifetimes are known, or the lifetimes where the concentrations are known. These studies provide a firm foundation for expansion of the applicability of this highly sensitive absorption technique for kinetic and spectroscopic investigation of chemical systems.