紫外光之液晶光配向及紅外線雷射之多光子吸收之研究

Abstract

一般的光配向，是使用汞燈照射紫外光，使得光配向劑透過單光子吸收的過程產生鍵結，進而配向。本實驗使用的光配向劑為LMWPC（Low-Molecular-Weight -Photo-Crosslinkable）型分子除了利用一般的汞燈照射紫外光（363 nm），透過光罩，製作出Fresnel zone plate的圖形，更利用紅外線雷射（Ti:sapphire laser 800 nm）在配向膜上掃瞄，經由雙光子吸收的機制，使得LMWPC也達到配向功效。 由實驗結果可以發現，一般單光子吸收的機制所需要的光源強度低，所需要的照光時間長（90 min），而雙光子吸收的機制所需要的光源強度強，但所需要的照光時間卻很短（數秒），因此未來可以利用雙光子吸收機制來進行光配向，可以更省時，也可以不用透過光罩，直接寫出任何想要的圖形來。

Rubbing on polyimide is a traditional method of liquid crystal (LC) alignment, and the method only can use on large surface alignment. Photoalignment is possible through the films of photosensitive polymer irradiated with linearly polarized UV light. This technique allows patterned alignment. We demonstrated the photoalignment using one-photon and two-photon absorption processes by irradiating a photosensitive film (LMWPC : Low-Molecular-Weight-Photo-Crosslinkable) material either with a UV mercury lamp or with a IR laser light respectively. In this study, we have been successful in using photo-induced alignment to make LC cells with Fresnel zone plate patterns. We have also demonstrated that two-photon absorption process was workable for molecule M1.