掺铁近化学配比铌酸锂晶体的紫外光致吸收和弛豫过程的研究

生长了系列掺杂低铁(质量分数分别为0×10-6,3×10-6,5×10-6,10×10-6,25×10-6,50×10-6、100×10-6)的近化学配比铌酸锂(SLN)晶体,测量了它们的紫外-可见光谱,并通过477nm处的线性吸收系数估算晶体中Fe2+和Fe3+的浓度。利用抽运(365nm)-探测(632.8nm)法测量不同掺杂浓度晶体光致吸收的动态过程和稳态特性,结果表明光致吸收是以扩展指数的形式衰减的,其衰减时间常数(即小极化子的寿命)随掺杂浓度和抽运光强增加而减小,扩展指数因子随抽运光强的增加而减少。根据电子的输运方程,利用四阶龙格-库塔方法对电子输运过程进行数值求解,模拟了掺铁铌酸锂(Fe:SLN)晶体的光致吸收的全过程,与实验所得结果符合得很好。

Ultraviolet-Light-Induced Absorption and Its Relaxation in Fe-Doped Near-Stoichiometric LiNbO3

Near-stoichiometric lithium niobate (SLN) crystals doped with low iron are grown, in which the mass fractions of iron are 0×10-6, 5×10-6, 10×10-6, 25×10-6, 50×10-6, 100×10-6, respectively. And their ultraviolet-visible transmission spectra are measured. The concentrations of Fe2+ and Fe3+ are estimated by the linear absorption coefficients at the wavelength of 477 nm. The dynamic process and steady characteristics of the light-induced absorption of crystals are investigated by the pump-probe (365 nm and 632.8 nm) method. The results show that the dark decay process of light-induced absorption exhibits a stretched-exponential behavior, and the decay time constant (i.e., the small polaron lifetime) decreases with the Fe-doped concentration and the pump intensity, while the stretching factor decreases with the pumping intensity. The electron transport equations are solved numerically by the four-order Runge-Kutta method, and the whole process of the light-induced absorption in the SLN crystals doped with Fe is simulated, which is consistent with the experimental results.