A new cylindrical photoacoustic cell with improved performance

We report a new design for an acoustically resonant photoacoustic cell with high performance. A cylindrical cell with suitable size was selected so that the resonant frequency of the first radial mode was equal to that of a longitudinal higher mode. The ends of the cell have a pair of thin coaxial tubes which lengths are 1/2 and 1/4 of acoustic wavelength λ, respectively. The λ/4 acoustic resonance makes a coupling between the first radial resonance and the higher longitudinal resonance, then leads to an acoustic energy concentrating in the middle of the cell. Thus, the surface loss was decreased, the acoustic quality factor and pressure amplitude increased obviously as compared with conventional radial resonant cylindrical cell. The ability to measure absorption coefficients as low as 2.43×10−9 cm−1 (1:1 signal to noise level) has been achieved.