在兆赫波段下PAA和MBBA兩種液態晶體的光學常數

Abstract

液態晶體的折射係數、吸收係數以及雙折射性，都是液態晶體在光學性質上的重要光學常數。兆赫波時域頻譜探測是研究物質在兆赫波段下光學性質很有用的一種方法，它可以提供我們在兆赫波通過待測物的電場強度以及相位的資訊。 我們利用兆赫波時域頻譜儀(THz-TDS)量測MBBA和PAA這兩種典型的向列型液晶。經由分析，實驗結果顯示MBBA液晶在兆赫波段下的雙折射率範圍為0.080 ~ 0.127，且在0.2 ~ 1.6THz範圍內沒有明顯的吸收頻譜。PAA液晶在溫度118℃的兆赫波段下的雙折射率約為0.06，且在0.2 ~ 1.2THz範圍內沒有明顯的吸收頻譜。

The refractive index, the index of absorption and the birefringence are all important optical constants in optics. Terahertz time-domain spectroscopy (THz-TDS) is an useful method to investigate the optical characters of the matters in THZ range, and it can provide the information of the phase and amplitude of the electrical field when THz wave passes the sample. We measure the two liquid crystals PAA and MBBA by using THz-TDS. It shows that the birefringence of MBBA is between 0.080 ~ 0.127, and there is no apparent absorption spectrum between 0.2 ~ 1.6THz. It shows that the birefringence of PAA at 118℃ is about 0.06, and there is no apparent absorption spectrum between 0.2 ~ 1.2THz.