| 摘要: | 本研究模擬石英玻璃當作基板，鍍上高反射鏡膜堆，再繪製出光柵（grating）結構，並在光柵結構上鍍製不同厚度之材料。光柵在雷射上的應用相當廣泛，而雷射光合束有分成兩種方式相干光束組合（Coherent Beam Combining, CBC）以及光譜合束（Spectral Beam Combining, SBC），而SBC系統為相對較簡單且有效的方式。研究重點在於利用RSoft模擬程式模擬出能使-1階反射率達到最高的多層介電質繞射光柵（multilayer dielectric diffraction grating, MDG）結構。
研究結果顯示，模擬結果顯示，在TE偏振模式下，當光柵的填充因子f=0.4時，鍍上Al2O3或HfO2均能顯著提升繞射效率，相較未鍍膜結構，效率最高可提升至99.99%以上。而在f=0.1的條件下，鍍上MgF₂亦可使繞射效率進一步提升，最高也可達 99.99%。為驗證模擬的正確性，本研究亦運用光柵繞射方程式進行理論計算，所得結果與RSoft模擬值相符，誤差小於2%，驗證了模擬方法的準確性，並支持鍍膜設計可有效提升光柵繞射性能的結論。
除了透過數學計算進行驗證外，本研究也從相位特性進行分析。結果顯示，在MDG未鍍膜時，其在中心波長1.064 µm下的相位無法達到±180° 或0°；然而，當鍍上Al₂O₃、HfO₂或MgF₂後，中心波長1.064µm的相位則能達到 ±180°或0°。
此外，本研究亦分析了電場分布對MDG結構的影響，繪製出不同鍍膜材料在達到最佳繞射效率時的電場分布圖。模擬顯示，當f=0.4且鍍上Al2O3或HfO2時，最大電場集中於鍍膜層內，可能導致局部熱效應與結構損傷，進而影響元件的耐久性。相對地，f=0.1且鍍上MgF₂時，電場強度則分布於光柵結構外部，有助於提升整體結構的熱穩定性。此結果顯示，該設計不僅可實現高繞射效率，亦兼顧光柵結構的穩定性，是一種具有應用潛力的優良MDG架構。
;This study simulates a quartz glass substrate coated with a high-reflectivity mirror stack, followed by the construction of a grating structure. Various materials with different thicknesses are then coated on top of the grating. Gratings have a wide range of applications in laser systems. Laser beam combining can generally be categorized into two types: Coherent Beam Combining (CBC) and Spectral Beam Combining (SBC). Among them, SBC is a relatively simpler and more efficient method. The focus of this research is to use the RSoft simulation software to design a multilayer dielectric diffraction grating (MDG) structure that maximizes the -1st order reflectivity.
Simulation results showed that, under TE polarization, the diffraction efficiency could be significantly enhanced by coating Al2O3 or HfO₂ when the grating duty cycle was f=0.4. Compared to the uncoated configuration, the maximum diffraction efficiency increased to over 99.99%. Furthermore, when f=0.1, coating with MgF₂ could also improve the efficiency, reaching a peak value of 99.99%. To validate the accuracy of the simulation results, theoretical calculations based on the grating diffraction equation were also performed. The analytical outcomes closely matched the RSoft simulation data, with an error margin of less than 2%, confirming the reliability of the simulation approach and supporting the conclusion that proper coating design can effectively enhance the diffraction performance of the grating.
In addition to mathematical verification, this study also analyzed the characteristics of the MDG from a phase perspective. The results show that, before coating, the phase at the central wavelength of 1.064 µm cannot reach ±180° or 0°. However, after applying coatings of Al₂O₃, HfO₂, or MgF₂, the phase at 1.064 µm reaches ±180° or 0°. This observation further confirms that the coated MDG can effectively enhance the diffraction efficiency at 1.064 µm.
In addition, this study also analyzed the impact of electric field distribution on the MDG structure and plotted the field distribution diagrams for different coating materials at their respective optimal diffraction efficiencies. Simulations showed that when f=0.4 and the grating is coated with Al₂O₃ or HfO₂, the maximum electric field is concentrated within the coating layer, which may lead to localized thermal effects and structural damage, thereby affecting the durability of the device. In contrast, when f=0.1 and coated with MgF₂, the electric field is mainly distributed outside the grating structure, which helps improve the overall thermal stability. These results indicate that the proposed design not only achieves high diffraction efficiency but also maintains structural stability, making it a promising MDG configuration for practical applications. |
