Design of DOE for the control of optical 'bubble' generated by highly focused radially polarized beam

摘要

In this paper, design of diffractive optical element (DOE) for optical bubble creating and controlling with radially polarized incident beam focused by a high numerical aperture (NA) aplanatic lens is proposed and its application in optical trapping is discussed. We use a DOE to modify the phase of the incident radial polarization beam to form different kinds of optical bubbles. Optimization algorithms are used to design the DOE to adjust the bubble size and depth to meet the requirements. The results show that the size of the bubble is inversely proportional to its depth. Owing to the overlapping of the field strengths around the focus, the bubble tends to merge into flattop distribution as it is getting smaller and smaller. With a fixed DOE design, bubbles with smaller size and larger depth can be generally obtained with higher NA, owing to a more confined field strength distribution from the strong longitudinal field component.