全光学非线性混频技术用于微裂纹检测的实验研究

发布时间：2019-01-07 07:28

【摘要】：采用全光学方法检测声波与开合裂纹相互作用后的非线性混频效应,达到检测裂纹位置的目的.激发光与加热光经过声光调制器后分别被调制为高频fH(几十kHz)激发光和低频fL(几Hz)加热光.裂纹会在低频加热光辐照下周期性开合,激发光激发出频率为fH的声波与裂纹相互作用后产生非线性混频信号(fH±fL),由测振仪或光偏转装置接收声信号并送至锁相放大器.实验中辐照在样品上的激发光、加热光和检测光光斑始终重合.随着三束光源逐步靠近裂纹中心,混频信号幅值逐渐增大.当增大到最大值后(三束光源达到裂纹中心区域),混频信号幅值开始逐渐减小(三束光源逐渐远离裂纹区域)最终趋于平缓,此时混频信号消失.光学激发的激发光可以聚焦到很小(约几十微米),所以其具有较高的空间分辨率.研究结果表明,利用非线性光声混频效应来检测裂纹的方法对实际的闭合裂纹的检测灵敏度远高于传统的线性激光超声裂纹检测方法,可为裂纹的光声无损检测提供新的解决思路和技术.
[Abstract]:An all-optical method is used to detect the nonlinear mixing effect after the interaction between acoustic wave and open crack, so as to detect the crack position. The excitation light and the heating light are modulated into high frequency fH (dozens of kHz) excitation light and low frequency fL (several Hz) heating light after they pass through the acousto-optic modulator respectively. The cracks are periodically opened and closed under the irradiation of low frequency heating light, and the excited light excites the interaction of the acoustic wave with the crack at the frequency of fH and produces a nonlinear mixing signal (fH 卤fL),) which is received by the vibrator or the optical deflector and sent to the phase-locked amplifier. In the experiment, the excited light irradiated on the sample, the heating light and the detection light spot always coincide. The amplitude of the mixing signal increases gradually with the three light sources approaching the crack center. When the maximum value is increased (the three beams reach the crack center), the amplitude of the mixing signal begins to decrease gradually (the light source is gradually far away from the crack area), and finally the mixing signal disappears. The optical excitation light can focus to very small (about tens of microns), so it has high spatial resolution. The results show that the detection sensitivity of the nonlinear photoacoustic mixing method is much higher than that of the traditional linear laser ultrasonic crack detection method. It can provide new solutions and techniques for photoacoustic nondestructive detection of cracks.
【作者单位】：南京理工大学电子工程与光电技术学院;
【基金】：国家自然科学基金青年科学基金(61405093) 江苏省自然科学基金青年科学基金(BK20140771)
【分类号】：TB302.5

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