Photopyroelectric thin-film instrumentation and impulse-response detection. Part II: Methodology

Frequency-modulation time-delay spectrometry (FM-TDS) has been implemented in photopyroelectric measurements of thermal diffusivity, on a series of well-characterized samples. The strategy of FM-TDS is sample excitation by a fast linear frequency sweep, whose autocorrelation function is mathematically equivalent to a Dirac delta function. The method permits the fast recovery of high-quality frequency and impulse-response information. Impulse responses recovered in the time-delay domain showed good agreement with a Green’s function model of transient heat conduction. The present work demonstrates that the FM-TDS measurement strategy yields photothermal information equivalent to that obtainable from a pulsed laser system, with much lower excitation power.