Transversely Excited Multipass Photoacoustic Cell Using Electromechanical Film as Microphone

A novel multipass photoacoustic cell with five stacked electromechanical films as a microphone has been constructed, tested and characterized. The photoacoustic cell is an open rectangular structure with two steel plates facing each other. The longitudinal acoustic resonances are excited transversely in an optical multipass configuration. A detection limit of 22 ppb (10(-9)) was achieved for flowing NO(2) in N(2) at normal pressure by using the maximum of 70 laser beams between the resonator plates. The corresponding minimum detectable absorption and the normalized noise-equivalent absorption coefficients were 2.2 × 10(-7) cm(-1) and 3.2 × 10(-9) cm(-1) WHz(-1/2), respectively.