Bandwidth-limited laser image projection using a DMD-based beam shaper

A digital micromirror device (DMD) laser beam shaper was implemented for projecting spatial bandwidth-limited laser images with precisely controlled intensity. A telescope images the binary DMD pattern with an adjustable pinhole low-pass filter that controls the system bandwidth and converts the binary pixelated image back to grayscale. Images with arbitrary but bandwidth-limited spatial frequency content are formed. System performance was evaluated by examining the spatial frequency response in terms of RMS intensity error by generating sinusoidal-flattop beam profiles with different spatial periods. This system evaluation was used as a reference to predict the error level of arbitrary output beam profiles. In addition, we demonstrated band-limited laser image projection for different spatial bandwidths using a grayscale image superimposed on a flattop laser beam profile. Optimized system bandwidth was simulated by considering the tradeoff between image precision and spatial resolution. Experimental results demonstrated that the RMS error of output beam profiles was consistent with the system evaluation reference. The major residual error in the output beam profile came from the sharp-edged pinhole low-pass filter. Error histograms had a Gaussian distribution with mean value of zero and standard deviation equal to the value of the RMS error. We plan to apply this technique to generate programmable optical trap shapes in ultracold atom experiments.

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