高速電子斑點干涉儀之研製-時進正交相移法的實證

Abstract

顯微技術經過多年之發展與改進，早已成為一個重要的精密量測方法與架構。隨著微機電與奈米科技之蓬勃發展，運用顯微技術來發展進一步檢測功能之儀器更是不勝枚舉。以全域檢測而言，高速電子斑點干涉術自1978年開始發展以來已超過25年，長久以來電子斑點干涉術皆以相移干涉術來將斑點光強訊號轉成相位訊號；然而，採用相移干涉術的同時也必須要在參考光路上引入相移裝置，對於儀器本身的開發而言將增加不少的成本，並且亦容易因為如壓電陶瓷驅動器一類常用相移機構本身的遲滯效應所產生的誤差，來造成量測結果準確性降低。因此本研究設計開發出一套具有奈米精度的全域動態光學檢測系統，並且從檢測系統中移除過往研究所常採用的相移裝置，藉由全新的光路設計和演算法，成功的利用一個光學元件來取代相移裝置，並且也因此省去繁瑣的量測調校步驟、進而大大的簡化了整個光路系統。 本研究承續前人的努力採用高速CCD為取像系統，但改於光路中加入八分之一波板於光路中來取代傳統的相移機構，再藉由極短的曝光時間和時序控制成功取得了振動物體一系列連續時間點之暫態資訊。在電子斑點影像處理方面，本研究以相關係數演算法結合時進正交相移法計算出相位主幅角、以中位數濾波法進行濾波、以路徑獨立之演算法完成相位重建工作，最後以多項式曲面擬合的技術完成物體完整的變形輪廓。在演算法方面，藉由證實時進正交相移法之可行性，將光路中的相移裝置移除，終於使得因為相位調制方法不精準所造成的誤差得到徹底的改善。 在實驗成果方面，本研究藉由LabVIEW圖控式程式語言開發出電子斑點影像處理介面，並且藉由光學模擬軟體先驗證光路之可行性，最後進行壓電待測物振動量測實驗，成功驗證了時進正交相移演算法之可行性。

After many years development and improvement, microscopy has been getting to be one of the most important precision metrology techniques. To meet the demand of the rapidly advanced micro-electro-mechanical system and nanotechnology, many instruments were invented by further integrating microscope into their systems. In the field of full-field measurement, high-speed electronic speckle pattern interferometry (ESPI) developed using high-speed CCD camera was first developed in 1978. Phase shifting interferometry was used to transform the speckle intensity information into the more desirable phase information. However, it is necessary to introduce a phase shifting device in the reference arm if phase shifting interferometry is to be implemented. However, adding phase shifting device significantly increases the system cost. Moreover, the measurement precision suffers due to the errors induced by the phase shifting device. For example, hysteresis of piezoceramic actuator can introduce errors in the range of several micrometers. The goal of this research is thus to develop a new ESPI system that can measure full-field and dynamic vibrations up to nanometer resolutions without the need to adopt the traditionally used phase shifting device. With the development of an innovative optical design and the associated signal-processing algorithm, phase shifting device is removed successfully from the optical system. Alignment and other related alignment and operational procedures is thus greatly simplified. In this dissertation, high-speed CCD camera was used as the image system. An eight-wave retardation plate was added within the optical path to remove the phase shifting device. By means of short exposure time and precise time sequency control, transient information in a series of time scales could be obtained successfully. In image processing part of ESPI, time stepping quadrature phase shifting method, direct correlation method, noise reduction median filter, and path-independent phase unwrapping method were all integrated to reconstruct surface profile of specimen. By demonstrating the feasibility of time stepping quadrature phase shifting method, we successfully remove the phase shifting device from the system and basically eliminated the errors induced by the inaccurate phase modulation. With regards to the experimental verifications, the electronic speckle image processing interface was developed by LabVIEW and the feasibility of the newly proposed optical configuration is demonstrated by optical simulation software. Finally, the feasibility of time stepping quadrature phase shifting method is verified experimentally.