近場之雙光子吸收致光電流對光電二極體元件之量測

Abstract

本論文研究最主要是利用本實驗室自製的近場光學顯微鏡系統量測光電二極體材料的電導特性。 由於近場所利用的光纖探針與其他光學元件造成之GVD使脈衝展寬(3.1ps)而降低脈衝能量，故我們利用一組平行光柵對補償並成功了壓縮展寬的脈衝，使其恢復到約有90fs的時間解析度。 為確定所使用的GaAsP光二極體材料對雙光子吸收的響應，我們利用此顆光二極體成功的架設了雙光子吸收自相關儀，當然其與倍頻訊號產生自相關儀比較也有相當多的優點，故成為現在量測脈衝的主要趨勢，當然我們也間接證明此顆光二極體對雙光子吸收的表現。 在近場光學顯微鏡量測上我們探測到了某個區域內的光電流訊號相對於其他位置有較高的響應，這呼應了之前利用He-Ne雷射與鈦藍寶石雷射之遠場量測響應不同，所以我們利用近場光學顯微鏡並結合超快鈦藍寶石雷射探測到了材料內能量交換上的差異，並可知道整個材料能階的均勻程度。

The main contribution of this thesis is the integration of the home-made NSOM system with the femtosecond Ti-Sapphire laser. As a first application in our lab, we characterize the photodiodes by two-photon induced photocurrent. To compensate the dispersion for pulses propagating in 2m-long fiber used in NSOM system and introduced by other optical components, we construct a grating pair pre-compensation system to compress the broadened pulse width from 3.12ps back to 90fs. Making sure that the TPA induced photocurrent in GaAsP photodetector as a sample we use, we set up the TPA autocorrelator system and successfully measure the 90fs pulses from our home-made Ti-Sapphire laser. It is surely a trend as measuring pulse width to replace the SHG autocorrelator. The GaAsP photodiode whose energy band gap is about 1.81eV can't be excited to induced current for such laser photon energy about 1.53eV but two photon absorption. For proving this, we measure the power dependence of the photocurrent and obtain the TPA phenomena of quadratic function. Using the NSOM system, we have performed preliminary experiment on the two-photon photocurrent response in 10mm’10mm area in our device. The same measurement is also conducted in far-field. The capability of the Near-field femtosecond two-photon-induced photocurrent system is established.