本論文主旨在研究不同之分子構型與其雙光子吸收行為之間的關連性。我們以對稱型分子架構為基礎，設計並合成出數個條型與多叉分支型的模型分子同時以飛秒脈衝式雷射為激發光源來測量這些模型分子的雙光子吸收性質。由雙光子激發螢光光譜、雙光子激發螢光壽命及雙光子激發螢光強度與入射光強度之依賴性等數項實驗的結果顯示，這些模型分子皆具有明顯的雙光子吸收行為。而在雙光子吸收截面之單點量測結果顯示，若在分子的分支上外接推/拉電子基或延長其分支之共軛結構，對其分子之雙光子吸收截面有提升效果；若將三叉型分子的分子結構加以延伸成為六叉型分子，其雙光子吸收截面也會隨著分子結構的擴展而有所提升；再者，在六叉型分子中，又以外圍分支結構上有外接推電子基的分子具有較高的雙光子吸收截面。另一方面，若將條型分子的分子結構加以延伸成為四叉型分子，其雙光子吸收截面卻意外地降低，但由於上述的雙光子吸收截面值只是單點量測的結果，目前還無法看出所有模型分子的雙光子吸收行為在較寬譜帶範圍的整體表現，所以還必須進一步量測出這些分子的雙光子吸收光譜才能有更深入的了解。在光學功率抑制效能的測試方面，我們選擇兩個模型分子來演示其雙光子吸收引起之光學功率限制的性質，量測結果顯示兩者皆表現出不錯的光學功率限制的行為。由非線性光學測量的結果得知，適當地延伸多叉型分子的π-共軛長度(或範圍)可以使其分子成為更好的雙光子吸收材料並有效地應用於光學功率限制器。 This thesis mainly attempted to study the relationship between molecular structures and two-photon absorption properties of several newly designed and synthesized model compounds. The two-photon- absorption-related properties of these model compounds were charac- terized by using high peak power infra-red laser pulses working in femto- second regime. The initial experimental results showed that the molecular two-photon absorptivity can be promoted either by proper extension of molecular π-conjugation length/domain or by incorporating electron- pushing/electron-pulling functional groups into the studied chromophore skeletons. Two-photon absorption based optical power limiting behaviors in the femtosecond time regime of two of these model compounds were also investigated. The results indicate that multi-branched structures with properly arranged expanded π-conjugation could be very effective two- photon absorbers and may be used as optical power limiters when against ultra-short laser pulses.
