High-precision laser beam shaping using binary-amplitude DLP spatial light modulators

Abstract

Laser beams with precisely controlled intensity profiles are essential for many areas of optics and optical physics. We create such beams from real-world lasers: quasi-Gaussian beams obtained directly from a laser and beam-expanding telescope without spatial filtering. Our application is to form optical standing-wave lattices for Bose-Einstein condensates in quantum emulators. This requires controlled amplitude and flat phase, and that the beam be free of temporal modulation from either pixel dithering or refresh cycles. We describe the development of the pattern design algorithms and demonstrate the performance of a high precision beam shaper to make flattop beams and other spatial profiles with similarly low spatial frequency content. The digital micromirror device (DMD) was imaged through a telescope containing a pinhole low-pass filter. An error diffusion algorithm was used to design the initial DMD pixel pattern based on the input beam profile. This pattern was iteratively refined based on output image measurements. We demonstrate forming a variety of beam profiles including flattop beams and beams with 1-D linear intensity variation, both with square and circular cross-sections. Produced beams had less than 0.25% root-mean-square (RMS) error with respect to the target profile and nearly flat phase.