以繞射元件產生無繞射光束

Abstract

本論文之目的在利用演算法設計繞射型相位元件，使其具有調制雷射光束在自由空間中強度分佈之功能。在此將進行無繞射光束之模擬，使其在自由空間中傳播一段距離後，仍保有相同之光點大小。 在此將採用雙片式繞射元件設計，第一片元件將雷射光束由高斯強度分佈轉換為貝索光束(Bessel beam)強度分佈輸出，並於此輸出平面加另一相位補償片，以抵消其相位，因此可以得到貝索強度分佈之準直光束。過程中，除了一方面提出方法改善楊-顧演算法遲滯效應外，將利用半導體製程或準分子雷射加工之方式進行實做，並對結果進行量測與分析，探討不同貝索光束大小設計對實際傳播距離之影響。

In this thesis, we use the iterative algorithm to design the diffractive optical elements (DOEs), which modulate optical beam in free space to form a given intensity distribution. Particularly, a non-diffractive beam can be generated with DOEs that keeps the same spot size in a certain propagating distance. In this work the DOEs for generating the non-diffractive beam consist of two DOEs. The first DOE transforms the field distribution of the input beam from Gaussian to the Bessel field distribution on the second DOE surface. The second DOE compensates the phase to form a uniform wave front along the propagating direction, i.e., a collimated beam with Bessel field distribution emerges. In this thesis, the convergence of the Y-G algorithm is improved and the DOEs are fabricated with laser LIGA. Some measurements and analyses of the DOE optical performance are made, and the experimental results are discussed.