Time evolution of laser-induced pyroelectric responses in a VDF/TrFE copolymer

Pyroelectric charge response induced by instantaneous heating using YAG laser pulse (7 ns) irradiation has been measured over a 1 ns to 10 s time range for a VDF/TrFE copolymer with composition 75/25 mol%. The observed spectra exhibited two damped oscillations associated with thermal expansion in the thickness and length directions coupled with piezoelectric effects. Removing these two components revealed pyroelectric responses consisting of an instantaneous component followed by a gradually increasing component. The instantaneous component appearing in parallel with the integrated laser intensity was attributed to primary pyroelectricity whose response time was <1 ns. The gradual component with time constant 200 ns was attributed to the relaxational nature of molecules and heat transfer from the electrode.