The 20th National Academic Exchange Conference on Optical Testing

Conference Venue

Exhibition Booth

Invited Presentation

FIS4 Spherical Dynamic Interferometer Based on Quadriwave Lateral Shearing Interferometry

When performing spherical surface metrology of optical components, it's inevitable to be affected by external environmental disturbances. For this reason, dynamic interferometers use a rotating wire grid polarizer for each pixel to obtain different phase shifts. The camera simultaneously acquires four phase-shifted interferograms, forming dynamic interferometers like Twyman-Green and Fizeau-type systems, thus eliminating the time required for four-step phase shifting. However, these are still dual-beam interferometry systems, and consequently, if the radius of curvature is too long, the fringes are prone to jitter, leading to unstable measurement results.

How to solve this problem? The FIS4 Quadriwave Lateral Shearing Interferometry sensor can effectively overcome the drawback of dual-beam interference fringe jitter. The FIS4 spherical dynamic interferometer utilizes a combined dual-interferometer system, as shown in Figure 1(a). The wavefront image acquisition interferometric system employs an FIS4 interferometric sensor with a randomly encoded hybrid grating. Because it is a common-path interferometry system, the interference fringes are very stable.

For optical path adjustment, a Twyman-Green interferometric system is used. This addresses the difficulty in observing the adjustment state where the focus F of the spherical aberration corrector coincides with the center of curvature C of the surface under test, which arises from the 2D grid interference fringes generated by the FIS4 interferometric sensor. Figure 1(b) shows a Twyman-Green interferometric system, where two beams pass through the reference mirror and the spherical mirror under test, allowing observation of the adjustment state where the focus F of the spherical aberration corrector coincides with the center of curvature C of the surface under test.

By using the combined FIS4 spherical dynamic interferometer shown in Figure 1(c), high-precision and stable measurement results can be obtained.