A PHOTOPYROELECTRIC METHOD WITH AIR AS THE THERMAL COUPLING FLUID

The photopyroelectric (PPE) technique is usually used as a contact pho tothermal method to characterize thin solid materials. We performed th eoretical and experimental investigations of a non-contact PPE configu ration to analyse the effects of an air gap between the thermal source and a PVDF sensor using a modulated laser beam as optical excitation. The detection of the thermal wave developed within the sample was pos sible across an air gap of up to 15 mm. The PPE signal was described w ell thanks to a two-dimensional (2D) model with axial symmetry, which could be reduced in some particular cases to a simpler 1D propagation model. Border effects can be artificially taken into account in the ca lculations by increasing the adiabatic lateral limits in the model, ke eping the active sensor area constant. Despite there being strong atte nuation with increasing modulation frequency, the PPE method can be us ed as well as can other non-contact photothermal techniques. New persp ectives for the application of the PPE technique have been opened.