We evaluate system performance of a high-precision beam shaper using a digital micromirror device (DMD) followed by a telescope with an adjustable pinhole low-pass filter. Beam shaping quality was measured by comparing the intensity and wave-front conformity with respect to the target image, and by the energy conversion efficiency. We previously demonstrated various flattop beams with high-precision intensity and a nearly uniform wave-front by using both coherent and incoherent light sources at visible and infrared wavelengths. The diffraction efficiency analysis determined optimized operation wavelengths for different diffraction orders. This paper extends beam shaping experiments to target images of a series of 2-D sinusoidal functions. An iterative pattern refinement process, based on the point spread function (PSF) of a single DMD pixel, was used to improve the image quality and to seek the optimized DMD binary pattern. Sinusoidal-flattop profiles with different spatial carrier frequencies were chosen for the purpose of system evaluation. Experiments demonstrated RMS error ranging from 0.95% to 11.87% in the raw camera image as the sinusoidal period was decreased. The DMD-based beam shaper achieved 1% RMS error level at low system bandwidth (large sinusoid period) and maintained 5% RMS error performance for a wide bandwidth range. We analyzed the relationship between spatial intensity error and system bandwidth. The ultimate system performance had amplitude error of ±1 to ±1.5 PSFs. Iterative refinement made a significant improvement in error for low system bandwidth as compared to the simulation of a DMD pattern designed by the error diffusion algorithm.

Date Published: 7 September 2011
PDF: 10 pages
Proc. SPIE 8130, Laser Beam Shaping XII, 81300C (7 September 2011);

Published in SPIE Proceedings Vol. 8130:
Laser Beam Shaping XII
Andrew Forbes; Todd E. Lizotte, Editor(s)