Control of coherent phonons with excitonic quantum beats

用激子量子拍控制相干声子

基本信息

批准号：
15340102
负责人：
NAKAYAMA Masaaki
金额：
$ 10.11万
依托单位：
Osaka City University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-15340102/
关键词：
GaAs AlAs multiple quantum well excitonic quantum beat coherent LO phonon pump-probe spectroscopy femto-second pulse laser subband-energy control terahertz electromagnetic wave CuI thin film テラヘルツ電磁波発生フォノン増幅 CuI薄膜量子閉じ込めシュタルク効果

项目摘要

We have investigated dynamical interactions between excitonic quantum beats and coherent longitudinal optical (LO) phonons in various GaAs/AlAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The time-domain signals were detected using time-resolved reflection-type pump-probe spectroscopy with a femto-second pulse laser. The excitonic quantum-beat energy is controlled by the quantum-size effect with a change of layer thickness and a quantum-confined Stark effect with a change of applied electric field. It is found that the intensity of the coherent GaAs-like LO phonon is drastically enhanced under the condition that the quantum-beat energy is resonant with the LO-phonon energy. The systematic results of the layer-thickness dependence and the pump-energy dependence clearly demonstrates that the excitonic quantum beat and coherent LO phonon couples with each other via longitudinal polarization, which results in the formation of a coupled mode, and that the polarization coupling acts as a driving force for the enhancement of the coherent LO phonon. The finding of the coupling between the excitonic quantum beat and coherent LO phonon provides us a novel paradigm of control of the coherent LO phonon with the excitonic quantum beat, which leads to manipulation of coherent phonons. Furthermore, we have demonstrated for the first time that intense and monochromatic THz electromagnetic wave with a frequency of 8.8 THz is generated by the coherent GaAs-like LO phonon in the MQW. In addition, we have investigated the coherent LO phonons in CuI thin films grown by vacuum deposition. It is found that the intensity of the coherent LO phonon is markedly enhanced under an exciton resonant condition of the pump-pulse energy, which suggests that impulsive stimulated Raman scattering dominates the enhancement of the intensity in the CuI thin film.

我们研究了分子束外延生长的各种 GaAs/AlAs 多量子阱 (MQW) 中激子量子拍和相干纵向光学 (LO) 声子之间的动态相互作用。使用飞秒脉冲激光器的时间分辨反射型泵浦探针光谱法检测时域信号。激子量子拍能量由随层厚度变化的量子尺寸效应和随施加电场变化的量子限制斯塔克效应控制。研究发现，在量子拍能与LO声子能量共振的条件下，类相干GaAs LO声子的强度显着增强。层厚依赖性和泵浦能量依赖性的系统结果清楚地表明，激子量子拍和相干LO声子通过纵向偏振相互耦合，从而形成耦合模式，并且偏振耦合起作用作为增强相干LO声子的驱动力。激子量子拍和相干LO声子之间耦合的发现为我们提供了一种用激子量子拍控制相干LO声子的新范式，从而实现了相干声子的操纵。此外，我们还首次证明了MQW中相干类GaAs LO声子产生频率为8.8 THz的强单色太赫兹电磁波。此外，我们还研究了真空沉积生长的 CuI 薄膜中的相干 LO 声子。研究发现，在泵浦脉冲能量的激子谐振条件下，相干LO声子的强度显着增强，这表明脉冲受激拉曼散射主导了CuI薄膜中强度的增强。