频谱非对称包络调制的圆对称艾里光束的传播特性研究

Propagation properties of circularly symmetric Airy beam modulated by spectral asymmetric envelope

为了增强圆对称艾里光束的自聚焦能力,本文使用了非对称双曲正割函数对光束的频谱进行了包络调制研究,详细探讨了频谱中高、低频分量对自聚焦特性的影响.结果表明单纯增加频谱的高频分量,并不会使自聚焦能力持续增强,低频分量对光束的自聚焦特性同样起着不可或缺的作用.由于非对称包络可以灵活的调节高、低频分量的比重,因此调制效果要优于高通滤波和对称包络调制.当调制参数选取适当时,光束焦点峰值大幅增加,达到了调制前的3.4倍,同时焦斑尺寸减小了23.6%.最后,本文对理论分析结果进行了实验验证,实验结果与理论结果相吻合,证明了频谱的非对称包络调制是一种高效且易于实现的调制方法.

An asymmetric envelope function for modulating the spectrum of circular Airy beam is proposed in this work.The propagation properties of the modified circular Airy beam are investigated in both theory and experiment.The three parameters of the asymmetric hyperbolic secant function can be used to adjust the ratio of the high frequency components to the low frequency components in Fourier space,and thus tuning the propagation properties of this modified circular Airy beam.The results demonstrate that the focal position is affected mainly by the high frequency components.The maximum focal intensity will not be enhanced continuously by increasing the proportion of the high frequency components.It depends on the ratio of the high frequency components to the low frequency components when the center frequency is determined.Therefore,using an asymmetric envelope in Fourier space is much more reasonable than using the high pass filtering or symmetric Gaussian envelope.The FWHM decreases significantly with the increase of center frequency.When the parameters are chosen appropriately,the size of focal spot will be reduced significantly,the maximum focal intensity,especially the abruptly autofocusing property will be enhanced greatly and the focal position can remain almost the same as the focal position of the common circular Airy beam.The maximum focal intensity of the proposed beam is 3.4 times that of the common circular Airy beam and the abruptly autofocusing property of the proposed beam is much better than that of the beam using the symmetric Gaussian envelope.The phase-only encoding method in Fourier space is used to generate the proposed beam in experiment.The experimental results are in reasonable agreement with the simulation results.It indicates that the modified beam can be generated conveniently by using the same method as that used to generate the common circular Airy beam.