利用自製單光儀分離並產生波長118.2奈米之皮秒真空紫外光雷射

Abstract

自從1970年代開始，雷射的成熟搭配非線性光學的發展，使得可應用的雷射光從長波長擴展到短波長波段，其中，真空紫外光波段是非常好的游離光源，且已經應用在許多研究上。舉例來說，真空紫外光游離偵測紅外光預解離光譜(Vacuum-Ultraviolet-Ionization-detected-infrared predissociation)可以用來了解氣體簇族分子間的結構和相互作用，而光共振增強多光子離子化法(REMPI )搭配飛行時間質譜儀，可以用來偵測原子和小分子的光譜，另外也被廣泛地運用在光分解離子成像(Velocity Map Imaging)上。在本論文中，作者和指導教授共同設計單光儀搭配三倍頻腔體和一可產生波長354.7 nm的皮秒雷射(Repetition rate：1 kHz, Pulse duration：~20 ps)，可將其三倍頻產生波長118.2 nm 真空紫外光，並和入射光分離，相較於一般利用三倍頻產生真空紫外光應用卻沒有和原入射光分離的方法，有著不被入射光影響的好處。接著參考Nicholas P. Lockyer 和 John C. Vickerman等人所整理之理論預測在不同條件下(光束大小和聚焦距離)產生最佳化波長118.2nm光所需之純Xenon氣體濃度，最後搭配我們所設計之偵測器量測產生的118.2 nm，在較低入射光能量(200、300J)時和理論預測相符，但隨著能量增強，最大訊號點無呈現等比級數的成長且漸漸向低濃度移動，在此我們推測為光學柯爾效應(Optical Kerr Effect)產生的影響，限制了可產生的最大真空紫外光能量。

Since the beginning of the 1970s, with the development of nonlinear optics and laser system, light source for experiment can be expanded from long wavelength range to short wavelength band. Among them, vacuum ultraviolet light is a very good ionization source, and has already been used in many researches. For example, Vacuum-Ultraviolet-Ionization-detected-infrared predissociation spectroscopy (VUV-ID-IRPDS) of clusters can be used to understand intermolecular structures and interactions at the microscopic level, and the Resonance-enhanced Multiphoton Ionization (REMPI) technique with time-of-flight mass spectrometry (TOFMS) can be applied to the spectroscopy of atoms and small molecules. This technique is also widely used in the Velocity Map Imaging (VMI) for electron kinetic energy analysis in photoelectron photoion coincidence spectroscopy. In this thesis, we design a monochromator combined with a tripling cell to generate and isolate 118.2 nm vacuum ultraviolet light by tripling the third harmonic of a Nd:YAG laser (354.7 nm, repetition rate：1 kHz, pulse duration：~20 ps). Compare to those simple methods to get VUV light to do experiment, using the isolated VUV light has the benefits that the experimental result won’t be affected by the original pump light. Then, using the theoretical calculation that discussed by Nicholas P. Lockyer and John C. Vickerman et al to predict the optimized pressure of Xenon needed to generate the highest VUV light power. At last, using the detector we designed to detect 118.2 nm VUV light. The experimental result are not quite match what we expect, that is the generated VUV power is proportional to the cubic of pump power. We think that is because of Optical Kerr Effect, limiting the maximum energy of generated VUV light.