提出了基于光热调制的激光声表面波检测疲劳裂纹的实验系统和方法，并将其用于发动机叶片疲劳裂纹的检测。NdYAG激光器产生的激光通过凸透镜聚焦在样品表面，同时用半导体激光在激发点同一位置进行光热调制，利用干涉仪在另一位置探测声表面波信号。利用精密平移台在可能的裂纹区扫描激发源和加热源，获得打开光热调制和关闭光热调制时的声表面波信号，也即不同位置处样品加热和冷却时的信号Sheat和Scool，由于光热调制产生的压应力使裂纹闭合，使Sheat产生明显的峰值变化，因此差值信号ΔS=Sheat-Scool即为疲劳裂纹闭合引起的信号变化。对叶片表面裂纹检测的实验结果表明，该方法具有较高的检测灵敏度和可靠性。

A method based on thermo-optical modulation of ultrasonic surface waves generated by laser for detecting crack of aircraft engine blade is presented. Crack closure on the blade due to laser-heating is considered in this method, thus two series of ultrasonic pulses including closure situation and original situation are both detected by interferometer when scanning the line source focused from NdYAG laser. The signals under heating by modulation signed with Sheat are compared with the cooling ones signed with Scool. The difference value between Sheat and Scool exhibits the effect of the crack closure because of the optical-thermal modulation. The results demonstrate that the crack on aircraft engine blade can be detected with reliability and high sensitivity.