近場時間解析光譜技術之研究

Abstract

本論文利用飛秒雷射當光源，架設雙色光激發探測量測系統，並與 自行架設的近場光學顯微儀結合成具飛秒級時間之解析近場顯微量測 系統。利用這套系統，我們已成功在GaSe0.6S0.4 晶體上量測到局域的近 場飛秒光譜。 因為光激發探測實驗是量測探測光上的調變訊號，其變化率只有 探測光強度的10-6~10-7，再加上光纖探針的光穿透率只有10-3~10-6、探 針上的金屬膜容易被超快雷射打壞，所以，近場量測到的光激發探測 訊號是非常微弱的。而我們嘗試使用各種方法來增加訊雜比，如用雙 色光激發探測、大角度的光纖探針、無鍍金屬膜的光纖探針和尋找適 合的近場操作模式，並且成功地得到初步成果。

In this thesis, we develop a femtosecond time-resolved scanning near-field optical microscopy by combining two-color pump-probe technique and scanning near-field optical microscopy. Now, we have measured local the near-field femtosecond time-resolved spectroscopy of GaSe0.6S0.4 crystal with this system. The pump-probe signals measuring by the NSOM fiber probe are very weak. That is because three reasons. One is the pump-probe technique must measure the modulation signal of the probe beam whose different intensity is only 10-6~10-7 of the probe beam intensity. Second is the transmission rates of the NSOM optical probes are 10-3~10-6. Third is the metal films which is coated on the fiber probe are easy broken by the ultralfast laser. Because the signal is very weak, we try to use many kinds of the methods for improving the ratio of signal-noise, for example, two-color pump-probe technique, larger cone angle of NSOM fiber probes, uncoating NSOM fiber probes and suitable operating mode of the time-resolved NSOM. Now we have got a initial result.