Abstract An generalized version of the Siegman formula which comes directly from Helmholtz equation is reported in this paper. Based on this formula, a comparison between the two definitions of the light beam far-field divergence angle is made. It is discovered the Siegman's moment definition for divergence angle would not make sense if the light beam could not be approximated to the slowly varying one. The proof of inequality M2≥1 given by Chen and Qiu would fail if the evanescence wave effects are considered.
Received: 25 May 1998
Revised: 06 October 1998
Accepted manuscript online:
PACS:
42.60.Jf
(Beam characteristics: profile, intensity, and power; spatial pattern formation)
Fund: Project supported Partly by the State Education Commission of China and by the Natural Science Foundation of Zhejiang Province (Grant No.196026), China.
Cite this article:
Sheng Zheng-mao (盛正卯), Yang Huan-xiong (杨焕雄) GENERALIZED SIEGMAN FORMULA AND COMMENTS ON THE INEQUALITY M2≥1 FOR LIGHT-BEAM QUALITY 1999 Acta Physica Sinica (Overseas Edition) 8 81
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