光源频谱宽度对Bessel光束亮暗梯度的影响

分析了三种不同频谱宽度的光源(激光、绿光LED和白光LED)产生无衍射贝塞尔(Bessel)光束亮暗环的梯度。分别模拟得到在不同位置的光强截面图，并计算各亮暗环的光强值，引入对比度的计算公式，计算了三种不同频谱宽度的光源产生贝塞尔光束亮暗环的对比度，可以得到频谱宽度越宽的光源产生的贝塞尔光束亮暗环之间的对比度降低，亮暗环强度梯度下降，从而导致囚禁粒子的能力降低。根据三种光源的特性设计了实验装置，并在与理论模拟相应的位置分别拍摄了三种不同频谱宽度光源产生的无衍射光斑图。对实验中拍摄到的光斑图进行对比度计算,可以得知频谱宽度越宽的光源产生的无衍射光束，其截面光斑亮暗环的对比度降低，亮暗环强度梯度降低，囚禁粒子能力下降，理论和实验相吻合。

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.