Assessment on the deviation from an ideal Gaussian beam for a real laser beam by Fresnel–Huygens phase-retrieval method
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The deviation of a real laser beam from an ideal Gaussian beam can be ascribed either to the non-Gaussianity of the intensity profile or to the non-planarity of the wave front at the beam waist. We demonstrate a method to differentiate these two causes. The contribution of the phase distortion at the beam waist to the deviation from an ideal Gaussian beam can be assessed from the change in modal spectrum when the wave front at the beam waist is replaced by a flat plane. The crucial information about the phase-profile function of the optical field at the beam waist for mode decomposition was calculated from two intensity profiles for different cross-sections around the beam waist using a convergent iterative algorithm based on the Fresnel–Huygens principle. Using a HeNe laser with its beam close to an ideal Gaussian beam for test, we found that both effects have comparable contributions to the deviation from an ideal Gaussian beam.
This work was supported by the Ministry of Science and Technology of Taiwan, Republic of China, under Grants MOST 104-2221-E-159-009 and MOST 105-2632-E-159-001.
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