A variable refractive null lens

Near-null interferometry using an aspheric null lens generating a broad range of variable spherical aberration for flexible test of aspheres

A null lens moving back and forth relative to a point source can generate variable spherical aberration for flexible test of aspheres. Different from the previous methods, variable spherical aberration null theory was developed by us to optimize the null lens. The optimized null was a plano-convex singlet containing a high order even asphere. Its attractive advantages are the simple structure and the broad range of testable surfaces. Most concave prolate conic and near conic surfaces with k∙R value varying between 0 and about 70000mm and with smaller relative aperture than that determined by each k∙R value can be tested. The testable asphericity range is between 0 and about 230λ. Relations among these testable surfaces were revealed as different groups of equidistant surfaces. To explicitly show the ability of the null, the measurable surfaces range map that contains all parameters defining a conic surface was offered. A practical near-null test system using this null was established. Alignment, near-null data processing, and error sources are analyzed in detail. To verify the broad testable surfaces range, three surfaces with widely varying amounts of asphericity were tested. Cross tests were provided to verify the test system accuracy.

Adaptive wavefront interferometry for unknown free-form surfaces

The primary problem of conventional wavefront interferometers is limited dynamic range. Unknown free-form surface figure error with large amplitude or slope is not measurable for too dense or invisible fringes. To troubleshoot this problem, we propose adaptive wavefront interferometry (AWI). AWI utilizes a wavefront sensor-less adaptive optics (AO) subsystem to intelligently speculate and compensate the unknown free-form surface figure error. In this subsystem, adaptive null optics is utilized to iteratively generate adaptive wavefronts to compensate the unknown severe surface figure error. The adaptive null optics is close-loop controlled (i.e., wavefront sensor-less optimization algorithms are utilized to control it by real time monitoring the compensation effects to guarantee convergence of the iteration). Ultimately, invisible fringes turn into resolvable ones, and null test is further realized. To demonstrate the feasibility of AWI, we designed one spatial light modulator (SLM) based AWI modality as an example. The system is based on a commercial interferometer and is easy to establish. No other elements are required besides the SLM. Principle, simulation, and experiments for the SLM based AWI are demonstrated.

Zoom null lens

A simple null lens is described that is moved back and forth relative to a point source to provide large amounts of variable wave front aberration. This device can be used to test a wide variety of optical components and systems.

Refractive null correctors for aspheric surfaces

The usefulness of a refractive null corrector is limited by how closely its aberrated wavefront can match the aspheric surface that requires testing. Guidance in both the design of the asphere to insure its nullability and the design of the null corrector is presented. A functional and constructional compendium of null corrector designs is proffered.

History of optics at itek

Itek Corporation was founded in 1957. A major business quickly developed in the manufacture of large precision optical systems principally for aerospace photography. While the company is now highly diversified, this work continues as a major activity. This article discusses the work of the group especially in the field of image formation as it has been described in the scientific literature. An outline is given of the historical roots in earlier laboratory programs beginning at Boston University in 1946 and at Harvard University in 1941.