以LCoS空間光調變器搭配Shack-Hartmann波前感測器之雷射光束整型系統

Laser Beam Shaping System via LCoS Spatial Light Modulator with Shack-Hartmann Wavefront Sensor

張祐誠(Yu-Chen Chang)

指導教授 ： 陳顯禎

國立交通大學/光電學院/影像與生醫光電研究所/碩士(2019年)

摘要

在許多雷射的應用當中會因為光強分佈非均勻而造成雷射加工不平整的問題，因此會需要光束整型的技術來把原先分佈不均勻的光強分佈改變成均勻的光強分佈。本論文是利用空間光調變器(spatial light modulator，SLM)，藉由迭代傅利葉演算法(iterative Fourier transform algorithm)設計電腦全像片的方式來顯示在SLM上借由繞射使雷射光強度分佈從原先高斯分佈變成平頂光束的強度分佈。然而實際的實驗上因為光路架設的問題或是可能在一些應用上會有一些外在的干擾讓雷射光繞射的結果不理想而造成平頂光束的強度分佈不均勻。這邊分別利用強度資訊反饋(intensity feedback)以及相位資訊反饋(phase feedback)來對光路當中的像差進行修補以改善效果。
利用強度資訊反饋是配合迭代傅利葉演算法來做像差修正，但此方法的效果有限。相較於利用強度資訊來反饋的修補方式，相位資訊的修補方式可以更為直接的去修補像差，預期的修補效果應該會比以強度資訊反饋來的好。當中相位資訊反饋利用自製的Shack-Hartmann波前感測器來偵測在相位資訊，能夠透過相位資訊的變化與空間光調變器上顯示的相位做比較，再利用相位共軛(Phase conjugation)的方法對量測到的像差進行修補。在強度資訊反饋的實驗上，方均根誤差從原始的40.8%改善至33%，光束整型的平整度有改善。另外在相位資訊反饋上面，像差改善上峰對峰值從2.63π修正到0.61π。因為Shack-Hartmann波前感測器空間解析度的受限，因此後續要整合到光束整型上需要配合改善硬體設計。

關鍵字

Shack-Hartmann波前感測器 ； 空間光調變器 ； 迭代傅立葉轉換演算法 ； 相位共軛

並列摘要

In many Laser applications, the Laser processing is not uniform due to the non-uniform distribution of intensity. Therefore, beam shaping technology is needed to convert the original non-uniform distribution of intensity to a uniform flat-top distribution beam. In this thesis, the spatial light modulator is used and designing the hologram by applying Iterative Fourier Transform Algorithm and displaying the hologram on spatial light modulator. The laser intensity distribution is converted from Gaussian distribution to flat-top distribution by diffraction. However, in actual experiments, the flat top intensity distribution is non-uniform owing to the errors in optical set up or extra disturbances. Respectively, intensity based feedback and phase based feedback are used to correct the aberration in optical set up here.
Intensity based feedback is done by using Iterative Fourier Transform Algorithm for aberration correction; however, the effect of this method is limited. Compared with Intensity based feedback method, phase based feedback method can be a better way to correct the aberration. By using lab-made Shack-Hartmann wavefront sensor to detect the wavefront information, it can compare the phase change with the wavefront on the spatial light modulator and correct the aberration by phase conjugation method. In the experiment of intensity based feedback, the root mean square error improves from 40.8% to 33%. Besides, in the experiment of phase based feedback, the aberration correction improves from 2.63π to 0.61π. Owing to the limit of Shack-Hartmann wavefront sensor’s spatial resolution, it is necessary to improve the hardware design in order to integrate with beam shaping system.

並列關鍵字

Shack-Hartmann wavefront sensor ； spatial light modulator ； beam shaping ； iterative Fourier transform algorithm ； phase conjugation

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