非线性克尔效应对飞秒激光偏振的超快调制  

Ultrafast polarization modulation of laser pulses at terahertz frequencies via optical Kerr effect

作　　者：林贤[1] 金钻明[1,2] 李炬赓 郭飞云 庄乃锋[3] 陈建中[3] 戴晔[1] 阎晓娜[1] 马国宏[1,2] Lin Xian;Jin Zuan-Ming;Li Ju-Geng;Guo Fei-Yun;Zhuang Nai-Feng;Chen Jian-Zhong;Dai Ye;Yan Xiao-Na;Ma Guo-Hong(Department of Physics,Shanghai University,Shanghai 200444,China;SIOM&STU Joint Laboratory for Superintense Lasers and the Applications,Shanghai 201210,China;College of Chemistry and Chemical Engineering,Fuzhou University,Fuzhou 350002,China)

机构地区：[1]上海大学物理系,上海200444 [2]上海光机所-上海科技大学超强超短激光及其应用联合实验室,上海201210 [3]福州大学化学化工学院,福州350002

出　　处：《物理学报》2018年第23期212-218,共7页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11604202;11674213;61735010;11774220);上海高校青年东方学者(批准号:QD2015020);上海市教育委员会和上海市教育发展基金会"晨光计划"(批准号:16CG45);上海市青年科技启明星计划(批准号:18QA1401700)资助的课题~~

摘　　要：研究了近红外飞秒激光的偏振在太赫兹频率的超快调制.利用抽运-探测光谱技术,通过改变两个脉冲之间的延迟时间可以控制光脉冲的旋转角.在Li:NaTb (WO_4)_2磁光晶体中观察到探测光的偏振随延迟时间变化的高速振荡,振荡信号的中心频率为0.19 THz.这种超快偏振调制现象可以解释为,抽运-探测实验构置中,前向传播的抽运光诱导的光学克尔非线性引起被晶体远端表面所反射的背向传播的探测光脉冲偏振面的额外旋转.通过改变抽运光的圆偏振旋性可以控制探测光调制信号的相位和振幅.实验结果表明,非线性光学克尔效应可以作为一种全新的手段,在磁光晶体中实现近红外飞秒激光以太赫兹频率的超快偏振调控.这将在超快磁光调制器等全光器件中得以应用.实验结果将有助于偏振依赖的超快动力学过程的研究.Polarized light has already been widely used for photography and display technologies.Magneto-optical Faraday effect,i.e.,the light polarization rotates in the magnetic field applied to the material in the direction of light propagation, plays a crucial role in the interaction between light and spin.Faraday effect allow us to understand the nature of magnetization in condensed materials.As an effect opposite to the Faraday effect,the magnetization can be induced in a transparent medium exposed to a circularly polarized electromagnetic wave,which is called inverse Faraday effect. Knowledge of the mechanism provides the opportunities of modulation devices in photonics,ultrafast opto-magnetism and magnonics.In this paper,we experimentally demonstrate a proof-of-concept ultrafast polarization modulation by employing circularly polarized light to demonstrate a strengthened terahertz (THz)frequency Kerr modulation signal, at room temperature.By using the transient pumpprobe spectroscopy with the reflected geometry,we are able to demonstrate the feasibility of such an ultrafast magneto-optical polarization modulation at 0.19THz in a paramagnetic Li:NaTb (WO4)2crystal with a thickness of 3mm.The time-resolved modulation signal is explained by the interaction between two counter-propagating laser pulses (central photon energy of 1.55eV)within the crystal via the optical Kerr effect.We find that the amplitude of the modulation increases with the pump fluence increasing,while the modulation frequency is dependent neither on the pump fluence nor on polarization of pump beam.However,it can further be found that the phase and amplitude of the transient Kerr modulation are strongly dependent on the helicity of the circularly polarized pump pulses.Indeed,these oscillating signals may be mistaken for spin excitation modes.The present findings allow us to get an insight into the transient magneto-optical dynamical process in transparent medium.In addition,the polarization modulation of ultrashort laser pulse on a picosecond time s

关 键 词：超快光谱 克尔效应 磁光效应 太赫兹 

分 类 号：TN24[电子电信—物理电子学]