激光超声位移场的共焦法布里-佩罗干涉仪检测技术

The technique of detecting the laser-ultrasonic vector displacement with a confocal Fabry-Perot interferometer

一般共焦法布里-佩罗(Fabry-Perot,FP)干涉仪只能检测声场的法向位移分量,而声场的切向位移分量含有法向位移分量所不能表达的材料特性。本文在检测声场法向位移分量共焦FP干涉仪的基础上,自行研制了一新颖的双通道共焦F-P干涉仪,它同时检测来自试样表面+θ和-θ角上的散射光,通过对两路输出信号作简单的信号处理,可以得到试样表面的位移点。用该F-P干涉仪测量了脉冲激光在Ti膜上激发的Lamb波的法向和切向位移,结果与理论预计一致。

Generally, a confocal Fabry-Perot interferometer is only able to detect the out-of-plane component of a displacement field; while the in-plane component often has the information about the material which cannot be found in this out-of-plane component. Based on a confocal F-P interferometer set-up for detecting the out-of-plane component of a laser generated acoustic field, a novel two-channel confocal F-P interferometer is developed. The scattering lights at scattering angle +θ and -θ from sample surface are received by this F-P interferometer. The displacement vector can be obtained with simple signal processing of two channel output signals. The out-of-plane and in plane displacement component of Lamb wave generated by a laser pulse in a Ti film are measured with this F-P interferometer. The experimental results are in good agreement with the theoretical predictions.