體積布拉格光柵的應用於雷射系統中已經愈來愈廣泛，對於雷射的光學性質提升如單色性、空間模態有很大的改善，故對體積布拉格光柵的研究也變得更加重要，然而以往的研究皆多以平面波入射的情形討論，不符合實際雷射輸高斯分佈的情形，因此本論文以平面波展開法考慮實際的雷射輸出，高斯光束條件下入射體積布拉格全像光柵，探討體積布拉格全像光柵作為雷射共振腔反射鏡時的等效長度；並由模擬結果得到的結論中發現，等效長度是由體積布拉格光柵的實際厚度以及繞射效率所決定，然而對於體積布拉格光柵而言，不同波長入射時繞射效率皆不一樣，故不同波長對應的等效長度不同；因此以VBG作為雷射共振腔反射鏡時，VBG的等效長度必須納入共振腔長的計算，導致不同雷射波長甚至不同雷射縱模會有不同等效共振腔長度，共振腔滿足駐波條件的波長因而改變，造成縱模間距呈現出不等間距，不同於一般認知以介電質反射鏡作為雷射共振腔反射鏡時等模間距之分佈。 Volume Bragg grating has been used in laser system widely, it can be utilized to improve laser optical properties, such as monochromatic, spatial mode properties. Therefore, the researches about volume Bragg grating have become more important. However, mostly previous studies assumed that the beam in the grating could be approximated by a plane wave, it is different from real laser output of Gaussian beam distribution. For the reason that this paper use plane wave decomposition to analyze the behavior of VBG in real situation, and investigate the effective length of VBG as laser cavity mirror. From the result of simulation obtain that the effective length of VBG depends on its diffraction efficiency and physical lengths. VBG has different diffraction efficiencies for each wavelength, so the effective lengths are different. The effective length of VBG should be consider when use VBG as laser cavity mirror, it will change the standing wave condition of the cavity. Cause that the longitudinal mode spacing are not equal, unlike normal situation has the same equal longitudinal mode spacing using dielectric mirror as laser cavity mirror.
