截断高斯光束的光束传输因子和焦移

采用三种不同束宽定义方法：熵束宽、环围功率和渐近分析法，研究比较了截断高斯光束的光束传输因子（M^2因子）和高斯光束通过光阑-透镜分离光学系统的焦移．结果表明，随截断参数艿的增大，三种方法计算的δ因子差异变小．当δ≥2．1时其M^2因子都趋于1，且三种方法计算的相对焦移亦相等。

The Beam Propagation Factor and the Focal Shift of Truncated Gaussian Beams

By using three different definitions of the beam width： the entropy-based width, power in the bucket and asymptotic analysis, the Beam propagation factor （ M^2 factor） of tnmcated Gaussian beams and the focal shift of Gaussian beams passing through an aperture-lens separated system are studied and compared. It is shown that with increasing truncation parameter δ, the difference of the M^2 factor calculated by means of these three methods becomes small. If δ≥2.1, the M^2 factor approaches 1 and the focal shift calculated by using these three methods is equal.