低频液体表面声波的光衍射效应研究

Study on the Diffraction Effects of Low Frequency Liquid Surface Wave

实验上采用频率为200Hz左右的低频液体表面波,其表面波波长约为2mm,观察到了清晰、稳定的衍射图样。并发现入射光掠入射时,其衍射图样非对称分布。理论上采用傅里叶光学的方法,得到了衍射光强度分布的解析表达式,根据这一表达式和实验上得到的衍射图样,可以得到表面波波长的实验测量值。提出了等效光栅常数的概念,等效光栅常数与表面波波长和入射方式有关。只要等效光栅常数与入射光波波长量级接近就可观察到衍射现象。理论上分析了衍射条纹对称性。光斜入射时,衍射条纹相对零级纹呈非对称分布,且随着入射角的增大,非对称分布的程度越大。

The high-visibility stationary diffraction fringes diffracted from low frequency liquid surface wave at about 200 Hz was observed experimentally. In circumstance, the wavelength is approximately 2mm. It was also found that its diffraction pat tern was asymmetrical when the light incidence is oblique. The analytical expression of the diffraction light intensity was derived theoretically by means of the Fourier optical method. According to this formula, the value of the surface wave wavelength can be achieved directly from the diffraction pattern. It was defined that the equivalent grating constant and the equivalent grating constant is related with surface wave wavelength as well as incident angle. As long as equivalent grating constant is close to the order of laser wavelength, the phenomenon of diffraction can observed easily. The diffraction fringes asymmetry was analyzed theoretically. When light oblique incidence, diffraction fringes relative to zero line was asymmetric. The bigger the angle of incidence is, the greater the degree of non-symmetrical distribution.