Modulation property of the high-power broadband laser beam propagation in free space

Abstract

We report on a numerical investigation of propagation property of high-power broadband laser beam in free space. We use Hankel transformation to solve Helmholtz equation numerically in the frequency domain. The modulation property of the broadband laser beam propagating in the Fresnel diffraction region is disclosed. It is found that the number of diffractive modulation rings equals to half the Fresnel number corresponding to the central wavelength of the broadband laser beam. The intensity modulation contrast of the broadband laser beam is smaller than that of monochromatic laser beam, suggesting that the broadband laser beam can suppress the harmful effect of near-field diffraction to some extent. Furthermore, it is demonstrated that the uniformity of near-field diffraction profile is determined by Fresnel number and bandwidth of the broadband beam.