基于空间光调制器获得空心光束的数值模拟和实验研究

光镊技术中,会聚的空心光束形成的能量光阱可用来捕获吸光性颗粒或操纵吸光性颗粒沿光轴方向运动。采用Gerchberg-Saxton(GS)算法计算所需相位,并将相位载入相位型空间光调制器来获得空心光束。为了提高会聚的空心光束能量,对空间光调制器相位屏进行预处理,叠加数字闪耀光栅位相,实现了将四个一级衍射谱闪耀至零级干涉极大位置,空心光束能量提高到原来的4.7倍。为了消除空间光调制器二维光栅结构所形成的零级谱亮斑以及高级谱的影响,在相位屏上加入球面波相位,使得空心光束衍射谱平面与零级谱平面的空间位置分离,并采用带通滤波器将空间光调制器的零级谱亮斑和高级谱滤掉。采用高度会聚透镜将所得空心光束会聚为微米尺寸,可应用于捕获吸光性颗粒。另外,利用离散傅立叶变换的平移原理实现空心光束实时平移,该方法可应用于实时操纵吸光性颗粒移动。

Numerical Simulation and Experimental Research of Hollow Beam Obtained based on Spatial Light Modulator

In optical tweezers technology, the energy optical trap formed by convergent hollow beam can be used to capture light absorbing particles or manupulate these particles moving along the optical axis direction. In this paper, Gerchberg-Saxton (GS) algorithm was used to calculate the phase, then the phase was loaded to a phase-type spatial light modulator to obtain the convergent hollow beam. To improve the energy of convergent hollow beam, the phase of spatial light modulator was preprocessed by overlaying a digital blazed grating phase, which makes the four first-order diffraction spectrum blaze to the zero-order position and the energy of the hollow beam increased to 4.7 times of the original energy. To eliminate the effect of zero-order diffraction spectrum caused by the two-demension structure of the spatial light modulator and the multi-order diffraction spectrum, the hollow beam spectrum plane is separated from the zero-order spectrum plane by overlaying a spherical wave phase, then a band-pass filter are used in the light path to filt the zero-order diffraction spectrum and the multi-order diffraction spectrum. The hollow beam can be converged to micro-scale by highly convergent lens, thus it can be applied to trapping light absorbing particles. In addition, the shift of the hollow beam are achieved in real time by the shift theory of the discrete Fourier transform, and the manupulation of light absorbing particle can achieved.