Wavefront Sensorless Aberration Correction With Magnetic Fluid Deformable Mirror for Laser Focus Control in Optical Tweezer System

The performance of wavefront corrector (WFC) plays a decisive role in the overall effectiveness of an adaptive optical (AO) system. When compared with commonly used WFCs, magnetic fluid deformable mirrors (MFDMs) have advantages of large stroke, low cost, and smooth continuous surface. However, the application of MFDMs is limited by the measuring range of the wavefront sensor (WFS) in the traditional AO systems. In addition, WFS needs one more optical path to measure the wavefront, which makes the AO system structure complex. In this article, a wavefront sensorless AO system based on MFDM is proposed to eliminate the limitations imposed by WFS. The stochastic parallel gradient descent (SPGD) algorithm is introduced in the control system to deform the surface of MFDM without the need to measure the wavefront. The MFDM with the proposed SPGD algorithm is applied to an optical tweezer system to eliminate the aberration caused by the optical system error and refractive index mismatch. Experimental results show that the divergent beam can be adaptively focused to successfully capture micro-particles.