Experimental and Theoretical Aspects of Frequency-Domain Photopyroelectric Spectroscopy of Condensed Phases (PPES), a New, Simple and Powerful Spectroscopic Technique

Abstract

Photoacoustic Spectroscopy (PAS) has been used extensively in recent years with conventional microphones and piezoelectric detectors as signal transducers. The commonest piezoelectric transducers are usually made out of piezoelectric ceramic (e.g., lead zirconate titanate, PZT [1 – 3]). These ceramics exhibit a much higher frequency response than microphone transducers, and thus they became dominant in photoacoustic applications where fast transducer response is required, such as pulsed laser PAS [4]. Very recently Tam and Coufal [5] and Coufal [6] used polyvinylidene difluoride (PVDF) thin film piezoelectric transducers for pulsed and modulated photoacoustics. These films have distinct advantages over PZT transducers, the most important of which being their much higher, essentially flat frequency response between DC and tens of MHz [7]. In addition to piezoelectric behaviour, PVDF thin films (Pennwalt KYNAR™) exhibit strong pyroelectric properties [8] and, therefore, they can be used as detectors of thermal radiation. Coufal [6] utilized the pyroelectric character of 9 ym thin PVDF films to obtain pulsed and low modulation frequency spectra of Nd₂O₃ doped poly(methyl methacrylate) films.