Influence of source spectral width on gradient between bright and dark rings of Bessel beams

The strength gradient in bright and dark rings of the non-diffracting Bessel beam for three kinds of different spectral width source (the laser, green LED and white LED sources) is analyzed. The profile of optical intensity distribution in different propagation distances is simulated, and the intensity of the bright and dark rings is calculated. The contrast of the bright and dark rings of the Bessel beam generated by the three different spectral width sources is calculated using the contrast formula. We find that the contrast and the strength gradient of the bright and dark rings reduce with the increase of the spectrum width. Therefore, the trapping ability of the Bessel beam is reduced. An optical system is designed according to the character of these three sources, and the profile of optical intensity distribution of the non-diffracting beam from these three different spectral width sources is captured. By calculating the contrast of the experimental result, we know that the contrast ratio of cross-sectional intensity declines, the ability of the trapping particles reduces with the increase of the spectral width. The experimental results agree well with the theoretical analysis.