使用擴散片降低雷射幾何擾動方法之最佳化設計與實驗驗證

Optimal design and experimental verification of a method for reducing geometrical fluctuations of laser by diffuser

林坤緯(Kun-wei Lin)

指導教授 ： 何正榮 ； 劉建聖

國立中央大學/工學院/機械工程學系/碩士(2013年)

摘要

本論文研究一種降低雷射光源幾何擾動的方法，由於雷射光源本身並非穩定的，因此在本論文中主要是將一轉動之擴散片加入系統中，使雷射光源通過後降低由於雷射之不穩定所產生的誤差。研究方法主要是利用ASAP光學軟體來模擬當光通過轉動之擴散片後產生的現象並根據成像光形來計算其重心位置，藉著重心位置變化量來判斷光源擾動程度，最後再搭配實驗驗證。
本論文系統架構茲說明如下：雷射光源通過一擴散片後，在其內部產生好幾次折射與反射並且透過轉動來使光強度均化，接著通過兩透鏡準直並聚焦，再通過兩濾光片來降低其光強度，最後藉由反射鏡將光源送至CCD上成像。由CCD所成像之光強度分佈來計算其重心位置，並根據此重心位置變化量來判斷光源擾動程度。通過實驗來得知光源所產生之重心位置變化量，並使用此結果來設定模擬的擾動量，最後模擬不同參數來分析其重心位置變化量與光強度分佈，根據其結果找出最佳化之參數，且搭配實驗來驗證模擬結果。
而根據模擬與實驗結果顯示，在系統中加入擴散片後相較於未加入時，其重心位置變化量有明顯降低，代表此法對於抑制光源擾動是有效的。

關鍵字

雷射 ； 光束強度 ； 幾何擾動 ； 光強度擾動

並列摘要

In this thesis we present a preliminary study and experimental results on the use of a system reducing the geometrical fluctuations of a laser, in which the effects of geometrical fluctuations of the laser beam are minimized by means of a high-speed rotating diffuser. A numerical model was implemented by using the ASAP ray tracing software to simulate the process when laser light passed through the rotating diffuser and an intensity distribution of the laser spot was recorded. Then the centroid calculated by the resultant intensity of the laser spot at different time is considered to be the extent of fluctuations. Finally, we simulated different parameters to analyze the variation of centroid and the intensity distribution of the laser spot, and find the optimal parameters.
The validity of the proposed system was verified by constructing a laboratory-built prototype. In this structure of the prototype, the light beam passed through a high-speed rotating diffuser and then the light beam was collimated and focused by means of two convex lenses and was incident on a CCD camera. According to the intensity distribution of the laser spot without diffuser, the centroid of the laser spot was calculated and then the geometrical fluctuations of the laser could be obtained at different time. The simulation and experimental results show that compared to the conventional system without diffuser, the variation of centroid with present system is much lower. It represents that the proposed method is effective for suppressing geometrical fluctuations of the laser beam.

並列關鍵字

Laser ； Geometrical fluctuations ； Diffuser

參考文獻

[2] J. A. Armstrong and A. W. SMITH, “Intensity fluctuations in GaAs laser emission,” Phys. rev., vol. 40, pp.155-164 , 1965.

[3] E. Jakeman, C. J. Oliver, E. R. Pike, M. Lax, and M. Zwanziger, “The intensity fluctuation distribution of laser light,” J. Phys. A: Gen. Phys., vol. 3, pp. 52-55, 1970.

[4] K. A. Janulewicz, C. M. Kim, and H. Stiel, “Speckle statistics and transverse coherence of an x-ray laser with fluctuations in its active medium,” Opt. Express., vol. 21, pp. 3225-3234, 2013.

[5] I. Takeshi, S. Machida, K. Nawata, and T. Ikegami, “Intensity fluctuations in each longitudinal mode of a multimode ALGaAs Laser,” IEEE J. Quantum Electron., vol. 13, pp. 574-579, 1977.

[6] A. Rüdigera, R. Schillinga, L. Schnuppa, W. Winklera, H. Billinga, and K. Maischbergera, “ A mode selector to suppress fluctuations in laser beam geometry,” J. Mod. Opt., vol. 28, pp. 641-658, 1981.