Thermal-wave resonator cavity

A thermal-wave resonant cavity was constructed using a thin aluminum foil wall as the intensity-modulated-laser-beam induced oscillator source opposite a pyroelectric polyvilidene fluoride wall acting as a signal transducer and cavity standing-wave-equivalent generator. It was shown that scanning the frequency of oscillation produces the fundamental and higher overtone resonant extrema albeit with increasingly attenuated amplitude—a characteristic of thermal-wave behavior. Experimentally, scanning the cavity length produced a sharp lock-in in-phase resonance with simple linewidth dependencies on oscillation (chopping) frequency and intracavity gas thermal diffusivity. The thermal diffusivity of air at 294 K was measured with three significant figure accuracy: 0.211±0.004 cm2/s. The novel resonator can be used as a high-resolution thermophysical property sensor of gaseous ambients.