PbB_4O_7晶体的太赫兹光谱和软光学声子

Terahertz spectra and soft optical phonons of PbB_4O_7 crystal

对实验测量的PbB4O7晶体样品的太赫兹(1012Hz)光谱、拉曼光谱以及红外—可见—紫外光谱进行了分析.在0.25—2.5THz波段介电函数随频率变化曲线ε(ν)出现共振型尖峰.四方面的分析表明PbB4O7晶体中存在软光学声子:1)介电函数随频率的变化曲线ε(ν)满足LST(Lyddane-Sachs-Teller)关系;2)在共振峰的频率附近(3.10THz)有很强的拉曼散射峰;3)吸收系数随频率的变化曲线α(ν)满足极化激元的特征;4)透过晶体的光子的色散关系ν(k)发生断开的畸变.PbB4O7晶体中存在软光学声子的意义在于,在满足产生极化激元的条件下,透过晶体的光子的频率会发生劈裂,分为升高和降低的两支,有可能利用这种原理来改变光子的频率.

The terahertz（1012 Hz） spectra,Raman spectra and infrared-visible-UV spectra are analyzed for PbB4O7 crystal sample.A resonance peak appears in the curve of the dielectric function ε（ν） in the frequency range of 0.25—2.5 THz.The analysis supports that soft optical phonons exist in PbB4O7 crystal from four aspects：1） the change curve ε（ν） of the dielectric function satisfies the Lyddane-Sachs-Teller relation;2） a strong Raman scattering peak appears in the vicinity of resonance frequency（3.10 THz）;3） absorption coefficient curve α（ν） meets the characteristics of polaritons;4） the dispersion relation curve ν（k） of the photon transmitting from the crystal reveals a frequency gap.The soft optical phonon exists in PbB4O7 crystal,which means that the frequency curve of the photon transmitting from the crystal will suffer splitting when the condition of producing polariton is satisfied.And the dispersion curve splits a higher branch and a lower one.This may help us find a new method of changing the frequency of the photon.