Three-dimensional imaging by sub-Nyquist sampling of white-light interferograms

Abstract

We demonstrate a simple way of increasing the data acquisition and processing speed in a scanning whitelight interferometer for surface topography measurement. The method consists of undersampling interference data and processing the resultant sub-Nyquist interferograms in the frequency domain to create complete threedimensional images. Experimental results on a 20-jrm step height standard show a measurement repeatability of 10 nm.

Laser interferometers for control of optical surface shape

“…In practice, this parameter is usually determined by number of interference fringes recorded by the CCD camera. A number of modern IF allows recording more than 1 000 fringes [23], and this fact makes it possible to perform AS test with quite large Fig. 3…”

“…In the first variant, the control unit is located in computer on special expansion board (PCI, PCI Express); CCD cameras are connected separately by the interfaces of USB 3.0. or Camera Link type. In the second case, the connection of interferometer and controlling computer through the interface USB 2.0/3.0 has a number of advantages: high speed of data transmission and capability of свыше 1000 полос [23], что дает возможность про-водить контроль формы АП с достаточно большим отклонением от ближайшей сферы. В этом слу-чае диаметр d диафрагмы (см.рис.1а) должен быть около ~8 мм.…”

Interference Fringe Signal Filtering Method for Performance Enhancing of White Light Interfrometry

“…[2][3][4][5][6][7] , 위상 정점 알고리즘은 간섭무늬 신호의 변화가 가장 큰 0차 오더 신호에서 정점을 추출하는 방식으 로 Larkin [8] , Sandoz [9] 방법이 대표적이다. 가시도 정점 검출 알고리즘으로 개발된 방법으로는 Fourier transform을 이용한 방법 [2][3][4] , 무게 중심법, 2차 다항식 맞춤 알고리즘 [5] , SEST (Squared-Envelope function estimation by Sample Theory) 방 법 [6] , 등이 제안되었으며, 최근에는 고속 알고리즘을 이용한 방식과 정점 검출 성능이 뛰어난 알고리즘을 병행하여 수행 속도가 빠르며 정점 검출 성능이 좋은 방법이 제안되었다 [7] . 본 논문에서 측정한 시료의 경우 배경 신호의 세기가 측정 위치에 따라 수시로 변하기 때문에 이러한 정점 검출 알고리 즘을 바로 적용하기 힘들며, 정점 검출 전에 전처리 과정이 필수적이다.…”

Dual Interferometer System for Measuring Index of Refraction

“…Therefore, there are more then 50 fringes under the coherence envelope for an interface (Figure 3.2). There are many publications that include algorithms for finding the center of a low coherence envelope, many of which report accuracies on the order of 5 nm or better (Danielson, 1990;Lee, 1990;Caber, 1993;de Groot, 1993;Hirabayashi, 2002). The biggest differences between their signals and the signals from Engage are the width of the coherence envelope and the overall fringe visibility.…”