High-precision laser beam shaping using a binary-amplitude spatial light modulator

Abstract

We have achieved high-precision laser beam shaping by using a binary-amplitude spatial light modulator, a digital micromirror device (DMD), followed by an imaging telescope that contains a pinhole low-pass filter (LPF). An error diffusion algorithm was used to design the initial DMD pixel pattern based on the measured input beam profile. This pattern was iteratively refined by simulating the optically low-pass filtered DMD image and changing DMD pixels to lift valleys and suppress peaks. We noted the gap between the experimental result of 1.4% root-mean-square (RMS) error and the simulated result for the same DMD pattern of 0.3% RMS error. Therefore, we deemed it necessary to introduce iterative refinement based on actual measurements of the output image to further improve the uniformity of the beam. Using this method, we have demonstrated the ability to shape raw, non-spatially filtered laser beams (quasi-Gaussian beams) into beams with precisely controlled profiles that have an unprecedented level of RMS error with respect to the target profile. We have shown that our iterative refinement process is able to improve the light intensity uniformity to around 1% RMS error in a raw camera image for both 633 and 1064 nm laser beams. The use of a digital LPF on the camera image is justified in that it matches the performance of the pinhole filter in the experimental setup. The digital low-pass filtered results reveal that the actual optical beam profiles have RMS error down to 0.23%. Our approach has also demonstrated the ability to produce a range of target profiles as long as they have similar spatial-frequency content (i.e., a slowly varying beam profile). Circular and square cross-section flat-top beams and beams with a linear intensity variation within a circular and square cross section were produced with similarly low RMS errors. The measured errors were about twice the ultimate limit of 0.1% RMS error based on the number of binary DMD pixels that participate in the beam-formation process.

A cold-atom Fermi–Hubbard antiferromagnet

“…The populated layer lies at the focus of a high resolution microscope system, which allows site-resolved detection of the lattice occupation and, at the same time, enables us to augment the harmonic lattice trap by projecting an approximately ring shaped potential onto the atoms from a DMD in the image plane. The ring centre contains the correct potential to prepare the subsystem Ω, while the rim of the ring is shaped to reduce the filling of the reservoir [37].…”

“…We address both challenges simultaneously by exploiting the high-resolution microscope at the heart of the experiment, which enables in situ, highfidelity, and site-resolved measurements of the lattice occupation. We use a digital micromirror device (DMD) as a spatial light modulator in the image plane of the microscope to control the atomic potential landscape at a single-site level [37]. We engineer the potential to split the system into two subsystems: a central disk-shaped region Ω containing > 75 sites, surrounded by a large reservoir at much lower density, see Fig.…”

“…The digital micromirror device (DMD) is a flexible tool for projecting nearly arbitrary light fields on the atomic system [37,[51][52][53]. The device is placed in the image plane of the system.…”

Solid-phase laser-induced forward transfer of variable shapes using a liquid-crystal spatial light modulator

“…Using a first-order approximation of the relation between gray level and phase retardance, the initial pattern of the SLM is calculated. A proportional feedback controller, inspired by Liang et al [25], is applied that iteratively improves the required phase pattern by comparing the desired beam shape to the beam shape measured by camera A. Figure 4 shows this measured beam shape after several iterations of the feedback loop for an arbitrary desired beam shape.…”

Adaptive electron beam shaping using a photoemission gun and spatial light modulator

“…Also, others have demonstrated light shaping using digital micromirror devices for beam instrumentation [20,21]. Apart from SLMs, micromirror devices may offer another option for high accuracy [22] drive laser shaping.…”