Multifocal spot array generated by fractional Talbot effect phase-only modulation.

We propose an approach for generating a multifocal spot array (MSA) with a high numerical aperture (NA) objective. The MSA is generated by using a special designed phase-only modulation at the back aperture of an objective. Without using any iteration algorithm, the modulated phase pattern is directly obtained by the simple analytical expressions based on the fractional Talbot effect. It is shown that the number of the spots in the focal region depends solely on the fractional Talbot parameter. By engineering the phase pattern with a large fractional Talbot parameter, a large number of focal spots can be created. Furthermore, the intensity distribution of each focal spot can be manipulated by introducing a composite spatially shifted vortex beam (CSSVB) as the incident field, leading to creation of various kinds of specific shaped spots. Consequently, the MSA composed of multiple individual spots with specific shape is created by focusing the CSSVB combined with the multifocal phase-only modulation. These kinds of MSAs may be found applications in parallel optical micromanipulation, multifocal multiphoton microscopic imaging, and parallel laser printing nanofabrication.