The sensitivity of thermal-lens and phase-shift (interferometric) techniques in photothermal spectroscopy: A comparative study

The thermal-lens and phase-shift (interferometric) techniques of phototherm al spectroscopy are studied theoretically for the coaxial and mutually orth ogonal propagations of probing and pumping beams. Respective expressions fo r the amplitude of detected signals are derived for the case of the volume absorption of pumping radiation. The sensitivities of the two techniques ar e numerically analyzed for different parameter values. It is demonstrated t hat the phase technique offers higher sensitivity especially if the size of the region with a perturbed temperature field is much larger than the prob ing beam radius. (C) 2000 MAIK "Nauka / Interperiodica".