A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

In this paper, we present a systematic control design and analysis for a two-dimensional nano-positioner. The primary emphasis of the paper is on the robustness of the closed-loop device as these flexure-stage-based, piezoactuated nano-positioners are nonlinear and operate in diverse conditions. To this end, we have used many tools from modern control theory to model devices and to quantify device resolution, bandwidth, and robustness. The implementation of this procedure for the simultaneous achievement of the objectives of robustness, high precision and high bandwidth is presented. The merits of the paradigm are demonstrated through experimental results.

Design methodologies for robust nano-positioning

http://www.nt.ntnu.no/users/skoge/prost/proceedings/ifac11-proceedings/data/html/papers/3537.pdf

Nanopositioning for storage applications

Evaluation of the superficial characteristics of articular cartilage using evanescent waves in the friction tests with intermittent sliding and loading

Evaluation of the effect of collagen network degradation on the frictional characteristics of articular cartilage using a simultaneous analysis of the contact condition

Phase shifting interferometry (PSI) is a highly efficient and accurate phase measuring method. The accuracy of PSI is most seriously impaired by calibration error and nonlinearity in the phase shifter. This paper presents a new algorithm, the overlapping averaging 4-frame (OAF) algorithm, which can reduce the phase error due to phase shifter errors. The relationship between the accuracy of OAF algorithm and phase shifter errors is given. From this relationship, it is verified that the OAF algorithm can reduce the phase error due to phase shifter errors. The computer simulation providing the magnitude of a calibration error and nonlinearity in the phase shifter are shown for a number of different phase-measurement algorithms. From the analysis, the result is obtained that the OAF algorithm is more highly accurate than other phase-measurement algorithms.

New algorithm on phase-shifting interferometry: the overlapping averaging 4-frame algorithm

The mechanism of frustrated total internal reflection was analyzed according to the theory of optical film. The transmission and reflection functions were developed and the curves of transmission and reflection changing from the relative gap width d / λ , incident angle θ 0 , and refraction index n were shown in graphs. We proposed a scheme of experimental device to test the theoretical conclusion. A self-made electronic actuator drove the piezoelectric ceramics of FTIR. Experiments showed that the evanescent of transmission is 80% for He–Ne laser and smaller for YAG laser and Er:glass laser.

Frustrated total internal reflection evanescent switching

This paper presents a system for measurement of CCD parameters that combines a photo-injection system and auto- focus systems. In the photo-injection system, a reverse microscope with plano-achromatic objective is used to produce a small light spot of (Phi) 2 micrometers . In the auto- focus system, astigmatic auto-focus method is applied. The auto-focus signal is detected by a simulation quadrate simulated by CCD. A piezoelectric transducer with high sensitivity and resolution is used to drive the focusing objective for a real-time control of the position of the small light spot which was required to be injected into one of pixels of CCD measured.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

System for measurement of CCD parameters

Based on introducing the principle and method of processing technique for interference pattern with step using the characteristic of phase-shift interferometry. The paper has discussed a new phase-unwrapping algorithm for the phase map containing discontinuities. The correct phase values in the presence of discontinuities, especially those caused by the object with height steps, can be obtained. This algorithm is fast and accurate. The results of the measurement of three- dimensional object with height steps are presented. These techniques have been successfully applied to measure the surface and wave aberration of the system with step.

Processing technique for interference pattern with step using phase-shift interferometry

Today, high quantities lens is more and more important to the optic-electric fields, and it brought about the demand of high accuracy testing of spherical surfaces. Absolute interferometric testing of spherical surfaces is a technical basis for establishing the spherical standard, and it is also an important application of computer aid interferometry. Partly work in the course of establishing the national spherical standard is introduced. A new method based on image processing has been developed instead of typical absolute testing which requires an eight-dimension mount whose cost is expensive and adjustment is very difficult. Interferograms sampled by phase-shifting interferometry can be processed to recognize the border of spherical surfaces. The key coefficients of position are in real time feedback to the operator to adjusting sphere precisely relative to the interferometer. This method can get more accuracy because of the high unison of three interferograms. This paper shows results of testing a 1/10 wave P-V sphere using two aplanats. It is easy to measure spherical surfaces to the accuracy better than 1/15 wave p- v.

Jinbang Chen

Papers

New algorithm on phase-shifting interferometry: the overlapping averaging 4-frame algorithm

Frustrated total internal reflection evanescent switching

System for measurement of CCD parameters

Processing technique for interference pattern with step using phase-shift interferometry

Realization of spherical absolute testing