Extended Helmholtz resonator in low-temperature photoacoustic spectroscopy

The acoustic transfer function of resonant PA cells is investigated experimentally and theoretically in the 10-300-K temperature range. The underlying cell design consists of two cavities that are interconnected by a cylindrical tube. The acoustic properties are treated in the scope of a generalized Helmholtz resonator model, which includes elements of acoustic transmission lines. For the low-temperature measurements the cell construction was modified to fit into a commercial optical cryostat. Photoacoustic signals are recorded from carbon and graphon samples as a function of the chopping frequency and of the temperature. With decreasing sample temperature the photoacoustic signal amplitude increases proportional to T(-2.75), as the phase angle and the resonance frequencies are simultaneously reduced.