Generating polymorphic and solenoid beams with an amplitude-type spatial light modulator

Helix-shaped polymorphic beams and solenoid ones are non-diffracting beams generated by the superposition of Bessel beams of specific orders. Their fields rotate around the beam propagation axis and have promising applications in optical forces, where they can be designed to function as either tractor or repulsor beams. Traditionally, phase-only spatial light modulators (SLMs) based on liquid crystal technology have been used for their generation. However, such SLMs have several limitations. They operate within a limited wavelength range, have lower refresh rates (typically 60 Hz, with a maximum of a few hundred Hz), and require linearly polarized light. There is, therefore, a need for an affordable alternative for applications outside the wavelength range of liquid crystal-based SLMs, for those requiring fast refresh rates or those needing polarization independence. In this work, we show, for the first time to the best of our knowledge, the generation of solenoid and helix-shaped polymorphic beams with an amplitude-type SLM, namely, a digital micromirror device (DMD). These address the aforementioned problems faced by liquid crystal-based SLMs. Although there are advantages associated with the use of DMDs, they often suffer from lower efficiency, mainly because many pixels are required to be in the off state. To solve this issue, we apply an intermediate plane holography method. We show that it can be used to generate a complex field helix-shaped polymorphic laser beam with a ∼2.5 fold improvement in optical power efficiency.