Choi J G, Diebold G J
Brown University, Chemistry Department, Providence, Rhode Island 02912, USA.
Appl Opt. 1982 Nov 15;21(22):4087-91. doi: 10.1364/AO.21.004087.
This paper describes a laser schlieren microphone, where a low-power He-Ne laser beam is deflected by a reflecting diaphragm mounted on an optoacoustic Helmholtz resonator. The sinusoidal pressure variations in the resonator distort the surface of the diaphragm so that the reflected laser beam is alternately focused and defocused. The deflection is converted into an amplitude modulation of the beam by an iris located at a distance from the resonator and detected with a photodiode. The light beam can be modulated at a high frequency and the signal from the photodiode processed with a lock-in amplifier so that noise with a power spectral density proportional to the inverse of the frequency is significantly reduced in the final optoacoustic signal. A mathematical description of the laser schlieren microphone is given that shows the system to respond linearly to small signals. An experiment was done to determine the range of linear response of the microphone to large amplitude optoacoustic signals.
本文描述了一种激光纹影麦克风，其中低功率氦氖激光束被安装在光声亥姆霍兹共振器上的反射膜片偏转。共振器中的正弦压力变化使膜片表面变形，从而使反射激光束交替聚焦和散焦。通过位于距共振器一定距离处的光阑将偏转转换为光束的幅度调制，并由光电二极管进行检测。光束可以高频调制，来自光电二极管的信号用锁相放大器处理，这样在最终的光声信号中，功率谱密度与频率成反比的噪声会显著降低。给出了激光纹影麦克风的数学描述，表明该系统对小信号呈线性响应。进行了一项实验，以确定该麦克风对大幅度光声信号的线性响应范围。
