An approach for achieving flattened laser intensity profile

Focusing of Gaussian beam by an apertured lens with spherical aberration is calculated,based on Huygens-Fresnel diffraction integral.The numerical results show that,when the coefficient of the spherical aberration is negative,one can obtain flattened laser intensity profile in two positions along the focused field.The effect of the limited aperture of the lens on the flattened laser intensity profile is investigated.It is shown that when Fresnel number of the lens become small,the positions where flattened laser intensity profile occur shift towards the focusing lens,and the lens with negative spherical aberration may be a simple approach for achieving flattened laser irradiance.