非傍轴截断双曲余弦高斯光束的M2因子

基于功率密度的二阶矩方法,对非傍轴截断双曲余弦高斯(ChG)光束的束宽、远场发散角和M2因子进行了研究.数值计算结果表明,非傍轴截断ChG光束的M2因子不仅与截断参数δ、偏心参数α有关,而且与初始束腰宽度和波长之比w0/λ有关.在δ足够小时,M2因子可小于1.当δ→ 0时,远场发散角趋于渐近值63.435°.对于α=0(Ω0=0)和δ→∞的特例,我们的结果分别退化为非傍轴截断高斯光束和非傍轴无截断ChG光束的M2因子.

M2 of nonparaxial truncated cosh-Gaussian beams

Based on the second-order moment of the power density, the beam width,far-field divergence angle and M2 factor of nonparaxial truncated cosh-Gaussian （ChG） beams are studied. It is found that the M^2 factor of nonparaxial truncated ChG beams depends not only on the truncation parameter δ, decentered parameter α, but also on the initial waistwidth to wavelength ratio ωo/λ. M^2 may be less than one when d is small enough. As δ→0, the far-field divergence angle approaches an asymptotic value of θmax = 63.435°. For the special cases of α = 0（Ω0 = 0） and δ→∞ our results reduce to the M^2 of nonparaxial truncated Gaussian beams and nonparaxial untruncated ChG beams, respectively