Design, Properties and Applications of Helmholtz Resonant Photoacoustic Cells for Measurements at Variable Temperatures

Helmholtz resonant cells offer advantages for variable temperature photoacoustic measurements, because they allow to keep the inner volume of the cells small and at the same time to separate the cooled or heated sample from the microphone and preamplifier which can be kept at room temperature(1-3). Since microphones and preamplifiers must not be heated, Helmholtz resonant cells are, in fact, the only appropriate design for high temperature experiments (3,4), while at cryogenic temperatures nonresonant cells may also be used(5). We constructed two resonant cells (2,3) which together are apt to cover the temperature range between 90 K and 1050 K. Both cells are supplied with two small valves used for gas exchange and pressure equilibration. Each cell is equipped with two heating filaments which allow the temperature of the sample to be stabilized with an accuracy better than 0.03 K. Temperatures are measured by Ni-Cr-Ni thermocouples or a platinum resistor.