KNbO_3:Fe晶体的最佳二波耦合  

OPTIMAL TWO-WAVE COUPLING IN KNbO_3:Fe CRYSTAL

作　　者：王威礼[1] 郑英俊[1] 王德煌[1] 张合义 让庆澜[1] 沈德忠[2] 童小林[2] 

机构地区：[1]北京大学物理系 [2]北京人工晶体研究所

出　　处：《发光学报》1991年第1期12-18,共7页Chinese Journal of Luminescence

基　　金：国家自然科学基金

摘　　要：本文在分析光折变晶体KNbO_3:Fe的最佳二波耦合条件的基础上,通过计算和实验研究了晶体KNbO_3:Fe的二波耦合增益系数Γ与两光束的夹角2θ、光栅矢量的取向β及不同电光系数r51或r42的关系,获得了在特定掺杂浓度N～10^(16)cm^(-3)条件下KNbO_3:Fe晶体的最佳二波耦合条件为:θm～4°—8°并且βm～45°.In this paper two-wave coupling in photorefractive KNbO3:Fe crystal is discussed in order to obtain the optimal conditions, under which the two-wave coupling exponential gain r reaches the maximum point.KNbO3:Fe crystal is an important photorefractive material.Its advantages are the fast response time and high sensitivity. The exponential gain r depends both on material propertiess,such as electro-optical tensor components rij and concentration of traps N, and on externally controlled parameters,such as the angle between the two incident beams inside the crystal 2θ, the angle between the grating vector and the crystal optical axis β,etc. We have studied two KNbO3:Fe crystal specimens with N1 = 1.8×1016cm-8 and N2 = 1.1×1016 cm-3 respectively. And one of them (the second one) is specially cut so that we can obtain β-value near 45° for small 2θvalue.We adopted an Ar+ Laser as the light source with the wave-length of 514.5 nm, which is separated into signal beam Iso and pump beam Ip0. We set r the ratio of Iso to Ipo on the optimal value: r = 1.0×10-4. The total input intensity is I0=Iso + Ipo = 12.0mW. For the first crystal specimen, we studied the contribution of two great electro-optical tensor components r51=l05pm/V and r42 = 380pm/V with different geometrical configuration of two-wave coupling. The theoretical and experimental results are demonstrated for the exponential gain r as a function of 0 and β, including the polarization status of incident beams, as in Fig. 2,3,4,5. For the second specially cut specimen, we carefully studied the exponential gain coefficient r as a function of β and θ, as shown in Fig. 6, and the optimal conditions were attained.Drawing a conclusion from our theoretical calculation and experimental results,we have obtained the following optimal two-wave coupling conditions in the KNbO3:Fe crystal with the concentration of traps N^1016cm-3: ( 1 ) the angle between the two incident beams 2θm^8°-16° and the angle between the grating vector and the crystal optical axis βm^45�

关 键 词：KNbO3:Fe 晶体 二波耦合 

分 类 号：O734[理学—晶体学]