Measurement investigation of an off-axis aspheric surface via a hybrid compensation method.

To measure the profile of an off-axis aspheric surface with large asphericity or lateral displacement, a hybrid compensation method is employed to realize a null test. First, the hybrid compensation method is simulated in MATLAB by using a fold sphere mirror and a computer-generated hologram (CGH) to compensate for the primary aberration and residual high-order aberration, respectively. For contrast, the hybrid compensation method is also simulated in Zemax by using dummy glass. Through comparing the simulation results from MATLAB and Zemax, the test CGH fringe positions from the two results are well matched. Then, the fold sphere mirror and CGH optical elements are designed and fabricated for an actual hybrid compensation measurement system, and the auto-collimation method is also used to detect the same off-axis aspheric surface. To ensure the correctness of the experiment, the result of actual hybrid compensation testing is contrasted with that of the auto-collimation method. Experiments show that the results obtained by the two methods are consistent, which indicates that this kind of hybrid compensation is an effective and accurate method for measurement of off-axis aspheric surfaces.