單一及混合液體的光致熱透鏡效應研究

Study of thermal lensing effect in single and binary mixture liquids

郭文瑜(Wen-Yu Kuo)

指導教授 ： 湯兆崙

國立中正大學/理學院/物理學系/碩士(2012年)

摘要

本論文使用中心波長817nm、重複率82MHz、脈衝寬度22飛秒(FWHM)的鈦藍寶石雷射以及Z-scan技術研究不同透明液體分子在飛秒時域下的熱透鏡效應。我們調查結構簡單的透明液體，例如CS_2 、烷基類、苯基類的分子，觀察不同分子的熱透鏡效應隨時間趨於平緩。我們使用出古典簡諧振子的現象模型描述三階極化電場，並配合拉曼感應克爾實驗結果以解釋透明液體分子巨觀上微弱的非線性吸收來自於受激拉曼散射造成分子內共振。高重覆率脈衝造成跨脈衝熱累積，使之觀察到熱透鏡效應。而混合不同溶液後其熱透鏡效應的增益應來自於溫度梯度造成的質量擴散，又稱為Soret effect。

並列摘要

We investigated the nonlinear absorptive and refractive properties of transparent liquids like carbon disulfide, alkyl group and phenyl group molecular using the Z-scan technique and a Ti:sapphire laser with 820 nm central wavelength, 82 MHz repetition rate, 21 fs pulse duration (FWHM) and 260 mW average power. Thermal lensing effect was observed for all liquids studied and it was found to increase with the pulse train width and gradually turn steady on the time scale of thermal diffusivity. Using classical simple harmonic oscillation motion and the result of the experiments of “Raman induced Kerr effect”, we described the heat contribute to the third order polarization which comes from the Stimulated Raman Scattering. And then, the high repetition rate pulses lead to the thermal lensing effect by the cross-pulse heat accumulation. In liquid mixtures, the interactions between different liquid molecules would enhance or weaken the thermal lensing effect which is a consequence of the buildup of thermally induced concentration gradients, or the so called Soret effect.

並列關鍵字

ultrafast laser ； Z-scan ； thermal lensing

參考文獻

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