紅寶石晶體的假性非線性折射率研究

Study of Pseudo-Nonlinear Refraction Index in a Ruby Crystal

黃隆祥(Long-Siang Huang)

指導教授 ： 陳慶緒 ； 魏台輝

國立中正大學/理學院/物理學系/碩士(2015年)

摘要

本論文利用單光束時間解析的Z掃描(time-resolved Z-scan)方法對紅寶石晶體進行假性非線性折射率的量測，此技術可以使用連續波雷射光源，應用在有居量透鏡效應的慢響應吸收體樣品，其實驗架構類似一般的Z掃描，但主要特徵在於必須將居量數密度達成穩定後的閉孔穿透率除以幫浦光剛打到樣品時的閉孔穿透率。我們使用的是波長為532 nm的連續波雷射光源，改變不同的入射光功率得到不同的divided Z-scan曲線，藉由曲線的特徵可以得到紅寶石對波長 532 nm的光具有居量透鏡效應引起的正透鏡效應，進一步由模擬可以得到居量透鏡效應造成的假性非線性折射率〖 n〗_2=1.26×〖10〗^(-8) cm^2/W和紅寶石的飽和吸收強度 I_s=979 W/〖cm〗^2。
當幫浦光在低功率時，我們能夠利用高斯分解法(Gaussian decomposition method,GDM)擬合實驗得到的divided Z-scan曲線，但是幫浦光在高功率時GDM擬合偏離實驗結果，所以需要利用其他方法如Hankel transform的繞射積分來擬合。此外，我們紀錄當樣品在Z-scan曲線歸一化穿透率的谷值處，其歸一化穿透率隨時間的變化，此變化帶有紅寶石亞穩態的本質螢光生命期和輻射再吸收的訊息，有趣的是此訊息並非直接測量波長 694.3 nm的螢光而是偵測直接通過樣品的 532 nm幫浦光，此方法提供另一種途徑研究輻射再吸收效應。

關鍵字

Z掃描 ； 輻射再吸收 ； 單光束時間解析Z掃描方法 ； 非線性折射率

並列摘要

In this study, we use a continuous-wave (cw) single laser beam to perform the time-resolved Z-scan, which is similar to a general Z-scan technique. The characteristics of the time-resolved Z-scan is that the transmission through the closed aperture at the time when the metastable state has been reached to steady populations, must be divided by the aforementioned transmission at the time when the metastable state is just pumped. We measure the pseudo-nonlinear refraction index of a ruby crystal that is a slow response absorber with population lens effect. The positive lens effect caused by the population lens effect was observed at 532 nm in our ruby crystal. We also obtain the divided Z-scan curves for different incident powers. Further simulations show that the pseudo-nonlinear refraction index n_2=1.26×〖10〗^(-8) cm^2/W and saturation intensity I_s=979 W/〖cm〗^2 for our ruby crystal.
The divided Z-scan curve can be fitted well by the Gaussian decomposition method (GDM) for a low pumping intensity but the fitting deviates from the experimental curve for a high pumping intensity so the Hankel transform method should be applied. In addition, we record the normalized transmittance with time when the ruby is located at the valley position of the divided Z-scan curve. This temporal evolution of normalized transmittance carry the information of the intrinsic lifetime of metastable state and the information of radiation reabsorption. Interestingly, the information about the intrinsic lifetime of metastable state and radiation reabsorption of ruby does not embed in the fluorescence of 694.3nm but in the 532 nm pump beam.

並列關鍵字

Z-scan ； nonlinear refractive index ； Radiation reabsorption ； time-resolved Z-scan

參考文獻

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