鉀原子氣體拉曼散射過程之研究和AgGaSe2晶體在紅外上轉換之應用

Abstract

本論文對原子氣體和光學晶體的一些非線性光學現象進行研究。 首先，我們在雷射調至鉀蒸氣接近4S-5P共振時，觀察4S-(5P)-5S和4S-(5P)-3D通道受激電子拉曼散射的競爭，此實驗結果顯示受激拉曼散射只發生在4S-(5P)-5S通道。在此拉曼散射下，放大自發輻射(5S-4P)的抑制被觀察到，四波混合過程對此受激拉曼散射的影響將被討論。在4S-(5P)-3D通道中，沒有觀察到對應受激拉曼散射(4S-(5P)-3D)的後向輻射，所以前向(5P)-3D輻射應為四波混合，而不是受激拉曼散射。其中放大自發輻射(3D-4P)來自放大自發輻射(5P-3D)，此放大自發輻射(5P-3D)可在後向觀察到。 其次，我們建立了由AgGaSe2和beta-BBO晶體組合成的雙晶體紅外上轉換器，能將11-16microns紅外輻射上轉換進入0.8microns範圍，此範圍可由靈敏的光電倍增管來測量。此上轉換器由beta-BBO光參量振盪器產生的1.7-1.8microns波段近紅外輻射所泵浦。 最後，我們測量了AgGaSe2在11-16microns中紅外範圍的尋常光和非尋常光折射率，得出0.85-16microns範圍的改良Sellmeier公式。在實驗中，11-16microns波段的中紅外輻射與近紅外1.7-1.8microns波段輻射在AgGaSe2晶體中混合。利用相匹配角的量測，尋常光和非尋常光折射率被計算出來，此近紅外輻射是由beta-BBO光參量振盪器所產生。

In this thesis some nonlinear optical phenomena in atomic vapor and optical crystal are discussed. Firstly, the competition of stimulated Raman scattering (SRS) between 4S-(5P)-5S and 4S-(5P)-3D channels has been observed as laser is tuned near 4S-5P resonance in potassium vapor. The experimental results show that the SRS only occur in the 4S-(5P)-5S channel. In this Raman scattering, the suppression of the amplified spontaneous emission (ASE) (5S-4P) has been observed. The influence of the four-wave mixing (FWM) processes on the SRS is discussed. In the 4S-(5P)-3D channel, in the backward direction no detectable emission corresponding to the SRS (4S-(5P)-3D) has been observed, so the forward (5P)-3D emission should be the FWM, not the SRS. The ASE (3D-4P) arises from the ASE (5P-3D), which can be observed in the backward direction. Secondly, a two-stage infrared up-convertor made of the AgGaSe2 and beta-BBO crystals has been built up, that can up-convert the middle infrared radiation of 11 - 16 microns range into the 0.8 microns range where the sensitive photomultiplier can be used. This up-convertor is pumped with a near infrared radiation of 1.7 - 1.8 microns wavelength range generated by a beta-BBO optical parametric oscillator. Finally, the refractive indices of AgGaSe2 for ordinary and extraordinary rays in the 11-16 microns mid-infrared range were measured and the improved Sellmeier equations from 0.85 microns to the 16 microns wavelength range were proposed. In this experiment, the mid-infrared radiations of the 11-16 microns wavelength range were mixed with a near-infrared radiation of the 1.7-1.8 microns wavelength range in AgGaSe2 crystal. With the measurement of phase-matching angles the refractive indices for ordinary and extraordinary rays were calculated. The near-infrared radiation was produced by a beta-BBO optical parametric oscillator.