Tunable binary Fresnel zone plates using a digital micromirror device
Fresnel zone plates use interference from alternating concentric opaque and transparent regions to focus light. In this study, we tailored Fresnel zone plates (FZP) to focus a beam with a wavelength of 633 nm at distances of 10, 15, and 20 cm from the zone plate. To allow for fast, on-demand focusing, the plates were uploaded to a digital micromirror device (DMD). With the FZPs, the light was observed to focus at 10, 16.5, and 23.5 cm, varying by 10% - 18% from prediction. The beam waists at the focus were measured and differed by four times from the theoretical. Nevertheless, FZPs allow for ``"lenses" with easily modifiable focal lengths.