本論文提出一種以光學干涉為基礎的新式位移量測技術－準共光程外差光柵
干涉術。由於結合了外差光柵干涉術與準共光程光路的設計，本項技術具有精密
的位移量測能力並且可以有效排除外部雜訊。外差干涉術是一種將待測信息載入
至光相位的量測方式，而光柵的繞射效應可將光柵的位移信息有效地轉換成光相
位改變。本研究利用氦氖雷射與電光調制器產生外差光源，經過準共光程光路設
計聚焦至高密度光柵，當光柵產生位移將會引入相位變化至各階繞射光，並且使
不同階數繞射光疊合產生干涉。透過鎖相放大器抓取外差光源的相位變化，即可
經由公式計算，進而獲得光柵位移情況。
根據理論推導，本系統的理論解析度優於3 pm。實驗結果分析，在電子雜訊
影響下，系統的實際解析度可以達到1.3 nm，量測準確度優於3.7 nm，靈敏度為
0.432 °/nm，系統的最大可量測速度為25 μm/sec。在長達一個小時的穩定度測試
下，系統總漂移量僅為23 nm。研究中也對所遭遇的量測誤差進行分析與討論，其
包含了系統誤差與環境誤差兩部份，此外，對於本系統的注意事項、物件所引入
的誤差、應用範圍與環境與也將進行討論。
由於準共光程的光路設計有效的降低外部雜訊影響，加上外差光柵干涉術原
有的優點，使得本系統具有高解析度、高靈敏度與高穩定度等的優點。

We describe a quasi-common optical path heterodyne grating interferometry to
measure the position of target which the grating hangs on. The system includes a
heterodyne light source, a designed quasi-common shearing optical path, a grating and a
lock-in amplifier for phase measurement. Then the heterodyne light is focused to the
grating. The optical phase variation which results from the grating movement will be
measured by shearing interference and the lock-in amplifier. With heterodyne shearing
interferometry, this measurement system has high accuracy, high measurement range,
high sensitivity, and high stability.
The theoretical shows that the resolution is 3 pm. In considering the electronic
noise, the experiment results demonstrate the interferometer resolution is 1.3 nm yet.
The system measurement accuracy is 3.7 nm, the sensitivity is 0.432 °/nm and the
maximum velocity measuring ability is 25 μm/s. In long term stability test, the total
displacement result is about 23 nm. In the study, the measurement errors, such as the
environmental error, the geometric error and nonlinearity error, are also discussed.

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