Yuhang He

Iterative algorithm for absolute planarity calibration in three-flat test.

An iterative algorithm is presented to calibrate the shapes of the reference surfaces in three-flat test. Three measurements in three-flat test determine the even part of the flat surfaces. The odd part can be obtained by adding one or more rotation measurements and using analytical recovery algorithm. Here we present an iterative algorithm to obtain the odd part instead of special analytical recovery algorithm. The iterative algorithm is purely numerical, and only involved in data rotation operation. A simulation experiment proves the validity and high accuracy of the proposed algorithm method.

Improved iterative algorithm for the three-flat test

Abstract. An iterative algorithm has been successfully used to process data from the three-flat test. On the basis of the iterative algorithm proposed by Vannoni, which is much faster and more effective than the Zernike polynomial fitting method, an improved algorithm is presented. By optimizing the iterative steps and removing the scaling factors, the surface shape can be easily computed in a few iterations. The validity of the method is proved by computer simulation, and the interpolation error and principle error are analyzed.

Computer-generated holograms for precision optical testing

Computer generated holograms (CGHs) are state-of-the-art components in optical systems, and are widely used in combination with standard Fizeau interferometers. The primary role of the CGHs is to generate reference wavefront with any desired shape. A method of interferometrically measuring large convex lens with CGHs is adopted, and the results from a set of experiments that demonstrate the accuracy and simplicity of performing the holographic test are presented. A direct comparison of the CGH measurement with results from a compensation method shows excellent agreement. Finally, measurement uncertainty due to substrate error and hologram fabrication processes is analyzed.

New reconstruction algorithm for absolute shape calibration in two-flat test

A new reconstruction algorithm for absolute shape calibration in two-flat test is proposed. The shift-rotation method is applied to absolute shape calibration in two-flat test. Relying on the decomposition of the reconstructed shapes into rotationally asymmetric and symmetric components, an iteration algorithm is presented to reconstruct the rotationally asymmetric components, and Zernike polynomial fitting algorithm is used to calculate rotationally symmetric components. Compared to the traditional algorithms, the proposed algorithm has the characteristics of considerable accuracy and less computational effort. A simulation experiment proves the validity of the presented algorithm.

Automatic stitching interferometry for large plano optics

The paper will describe an automated subaperture stitching interferometry for large plano surface based on relevant algorithm, which restruct the whole surface without recording the position of every subaperture. Both correction and data fusion algorithm are used to minimize the stitching error.

Errata: Improved iterative algorithm for the three-flat test

The corresponding author for this article [Opt. Eng.. 53, (9 ), 092004 (2014)] has been changed from Bo Gao to Liqun Chai. The paper was corrected online on 4 June 2014.

Absolute Measurement of Square flats with Legendre Polynomial Fitting Method

Zernike Polynomial fitting method is an effective way to reconstruct absolute surface for three-flat test. However, the Zernike circle polynomials are not orthogonal over the circular area, hence they are not suitable for square flat. We present an absolute testing of a square flat with Legendre polynomial fitting method, which relies on calculating the coefficients of the Legendre terms by least-square fitting method. To obtain the three-dimensional surface data, one additional measurement that rotate the test flat through 90° should be introduced. The formulas are derived theoretically in detail, and validity has been proved by simulated experiment. Vertical profiles of the three surfaces are compared with the measurement results obtained by three-flat test. Good agreement validates our method.

Lens wavefront measurement technique with a reflective Fresnel-zone hologram

A new technique for precise wavefront measurement of lens with a hologram is presented. In diffraction, the Fresnel-zone plate hologram emulates the reflective properties of a spherical mirror for use during transmission null tests of an optic by use of a phase-shifting interferometer. Experiment shows that the Fresnel-zone hologram method result is quite similar with that of the traditional interferometry testing method, in which retroreflecting spherical surfaces are used as the reference. The benefit of this methodology is the higher degree of precision at lower cost of manufacturing the reflecting hologram, compared with retrospheres capable of delivering similar precision. This technique is widely applicable and is particularly useful for measuring long focus lens.