中文摘要：

导出二维光栅衍射光斑的位置公式,讨论其衍射图样的特性,并给出实验演示效果.提出一种通过衍射图样照片测量光栅常数（或波长）的方法.

英文摘要：

The position formula for the diffractive light-spot of two-dimensional grating is derived. The property of diffraction pattern is discussed and its experimental demonstration is given. A new method of measurement of grating constant is presented.