Formation of a doughnut laser beam for super-resolving microscopy using a phase spatial light modulator

The formation of a doughnut-shaped laser beam is presented. To generate the beam, we use an optically addressed parallel-aligned nematic liquid-crystal phase spatial light modulator (PAL-SLM), and observe the shape of the focused beam. By using a compensating technique for wave aberration, the beam has a symmetric doughnut shape with a hole size of 1 μmφ on the focal plane. The experimental result shows that the generated beam can be expected to be applicable to super-resolving microscopy based on the fluorescence depletion process.