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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。
Experimental use of frequency of about 200Hz low frequency liquid surface wave, the surface wave wavelength of about 2mm, observed a clear and stable diffraction pattern. It is found that the diffraction patterns of the incident light are non-symmetrical when grazingly incident. In theory, the analytical expression of the intensity distribution of diffracted light is obtained by the Fourier optics method. Based on this expression and experimental diffraction patterns, experimental measurements of the surface wave wavelength can be obtained. The concept of equivalent grating constant is proposed. The equivalent grating constant is related to the wavelength and incident mode of the surface wave. The diffraction phenomenon can be observed as long as the equivalent grating constant is close to the order of the wavelength of the incident light. The diffraction fringe symmetry is theoretically analyzed. When the light is obliquely incident, the diffraction fringes are asymmetric with respect to the zero-order fringes. As the incident angle increases, the degree of asymmetric distribution increases.