High-precision Laser Beam Shaping and Image Projection

Monday, March 1, 2010 - 12:00pm

By Jinyang Liang
Professor: Michael F. Becker;
Affiliation: Optical Signal Processing Laboratory (OSPLab)

The Optical Lattice Emulator (OLE) program, led by Nobel Laureate Professor Wolfgang Ketterle of MIT and funded by DARPA, strives to build a solid-state material emulator by using ultracold atoms in an optically defined lattice in collaboration with eight other prestigious universities in the US and Europe. UT ECE Professor Michael Becker and graduate student, Jinyang Liang, are researching high-precision laser beam shaping and image projection, in order to form a controllable optical lattice that will be used to program the emulator. A flat-top beam is defined by a beam profile with uniform intensity distribution at the center created through high-precision control of the amplitude and phase of light. The flat-top beam will be used to produce a standing wave, which creates a uniform optical lattice potential. In atomic physics, a flat-top beam can improve the sensitivity of interferometric gravity wave detectors and be used in ultracold atom experiments. UT ECE in collaboration with the UT Department of Physics plans to contribute to the OLE program by applying this technique to form a three-dimensional optical lattice and control states of ultracold atoms for Bose-Einstein Condensate (BEC) experiments.

Using the state-of-art facilities in Professor Becker’s Optical Signal Processing Laboratory (OSPLab), we have achieved high-precision laser beam shaping by employing a binary-amplitude spatial light modulator, the Texas Instrument Digital Micromirror Device (DMD), followed by an imaging telescope that contains a pinhole low-pass filter (LPF) (Figure 1). This experiment demonstrates the ability to shape raw quasi-Gaussian laser beams into beams with precisely controlled profiles that have an unprecedented low 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 nm and 1064 nm laser beams (Figure 2). The digital LPF of the camera image matches the performance of the pinhole filter in the experimental setup. The digital LPF results reveal that the actual optical beam profiles have an RMS error down to 0.23%.


Figure 1 Optical layout of the beam shaping system producing one-dimensional optical lattice


Figure 2 The top view and cross section of the flat-top beam with regional flatness

Our approach achieves an unprecedented low error level. With an attractive flexibility, it has also demonstrated the ability to produce a range of target profiles of similar spatial frequency content (slowly-varying beam profile). Finally, our results indicate that this beam shaping technique is sufficiently accurate to form the standing wave optical lattice needed for ultracold atom experiments. In the future, we plan to implement our technique in OLE experiments with 87Rb bosons in a Bose-Einstein Condensate. Meanwhile, we would like to validate the uniform density profile of atoms in the lattice and develop feedback control of the lattice potential using a measured atom density distribution. In addition, we plan to continue investigating the high-precision beam shaping technique in order to achieve the best result for an arbitrary target function with any spatial frequency distribution. Some additional applications include high-precision image projection in biomedical engineering, optical probing techniques in semiconductor fabrication, and fluorescence testing in chemistry.