以非同調光源及飛秒雷射光源研究Rhodamine B之超快動力學

Abstract

在本篇論文中，我們利用兩種不同光源之系統架構量測雷射染料分子Rhodamine B之超快動力學，實驗中分別使用非同調光源及飛秒雷射光源。 首先，本實驗利用非同調LED白光光源量測於不同溫度下Rhodamine B染料分子之失相時間。在過去的文獻中，大多利用光子回波技術搭配飛秒雷射光源及四波混頻架設系統，完成失相時間的量測。而本論文最大的不同，為光源的使用，本研究使用LED做為量測訊號的光源，因為LED光源具有近飛秒等級的高時間解析度，利用此量測技術，我們將討論失相時間與溫度的相關性。 二為利用自行架設的NOPA(Non-collinear parametric amplifier，非共線光參數放大器系統研究Rhodamine B染料分子載子超快動力學。透過NOPA系統所產生的10飛秒脈衝及多頻道鎖相放大器(Multichannel lock-in amplifier)可將各波段(520 nm~700 nm)所偵測到的超快動態反應清晰完整的紀錄。此高頻率、高時間解析的雷射統非常適合用來探測光化學反應裡中間物質的產生過程以及分子結構的動態變化情形。

In this thesis, I have studied ultrafast dynamics of a laser dye, Rhodamine B, by two different techniques using incoherent light source and femtosecond laser pulse. Thus, the thesis consists of the corresponding two parts. First, I have used a white LED as an incoherent light source to measure dephasing time of Rhodamine B at different temperature. The dephasing time is generally measured by photon echo measurement using a femtosecond laser pulse in a complicated four-wave mixing setup. However, the present work demonstrates that the deplasing time of the sample can be studied using the LED light. The LED light has ultrashort coherence time, thus an interferometer with the light source provides ultrafast time resolution. The ultrafast dynamics observed in the experimental result estimated the dephasing time dependent on temperature. Second, the homemade NOPA (non-collinear optical parametric amplifier) system was used to generate ultrashort visible laser pulse for ultrafast time-resolved absorption spectroscopy of the Rhodamine B. The sub-10 fs laser pulses with broadband visible spectrum has elucidated the ultrafast relaxation dynamics of electronic populations.