Focusing of flattened Gaussian beams by an annular lens |
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Authors: | Xiaoling Ji Baida Lü |
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Institution: | a College of Electronic Engineering, Sichuan Normal University, Chengdu 610066, People's Republic of China;b Institute of Laser Physics and Chemistry, Sichuan University, Chengdu 610064, People's Republic of China;c State Key Laboratory of Laser Technology, Huazhong University of Science and Technology, Wuhan 430074, China |
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Abstract: | Focusing properties of flattened Gaussian beams (FGBs) passing through an annular lens is studied based on the Collins formula. It is found that the on-axis irradiance distributions of focused FGBs are unsymmetrical with respect to the geometrical focal plane even for large values of Fresnel number Fw associated with the beam, so that there exist focal shifts in general. Detailed numerical results show the dependence of focal shifts on the beam and system parameters. Focal shifts of FGBs by a lens without central obscuration and focal shifts of Gaussian beams by an annular lens can be treated as special cases of the obscure ratio =0 and beam order N=0, respectively. Furthermore, focal shifts of plane waves by an annular lens can also be treated as a special case of N=0 and Fw→∞. |
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Keywords: | Focusing Focal shift Flattened Gaussian beam Annular lens |
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