A NOVEL COUPLED RESONANT PHOTOACOUSTIC CELL （T-TYPE）

This paper describes the design and characters of a novel coupled resonant photoacoustic cell. It is called T-type cell, because it consists of two cylinders, one is thin and long, another is wide and short. Its resonance frequencies are calculated on the basis of pressure integral expression in a cavity and Green's function. The coupled resonence frequencies of a prototype of T-type cell are calculated numerically and examined experimentally. The experimental and calculated results are in good agreement. With the CO₂ laser photoacoustic spectrometer the measured results of the T-type cell prove that it has a high quality factor Q (up to 900). When the length of the cell's small cylinder equal's to 3λ/4, another resonance occures; at this frequency the background signal is in opposite phase with photoacoustic signal. Therefore it becomes possible to record in real-time the PA absorption spectra of samples (background signal having been substracted). Its detection sensitivities for vapor concentration for CH₃OH and C₆H₆ have reached 3\rm \times 10^-8/W\sqrt Hz \ and \7\rm \times 10^-8/W\sqrt Hz respectively.