Active alignment technique of an off-axis beam expander

Catoptrical systems fall into 2 broad categories: On-Axis and Off-Axis. The alignment of off-axis mirror-based optical systems are non-trivial compared to conventional on-axis mirror designs because of the lack of a central optical axis. To align an off-axis mirror-based laser beam expander (consisting of 2 off-axis parabolic mirrors), we have developed an alignment technique that is systematic, quantitative, and reproducible. This is a quick and efficient method of alignment that is based on wavefront sensing and its corresponding correction based on the Zernike polynomial coefficients. In this paper, we highlight the key elements of the beam expander's design and detail the steps of the opto-mechanical alignment process as well as the performance results of the system after successful alignment.