Theoretical analysis and experimental study of Fourier transformation of Franz-Keldysh oscillations in GaAs

Fourier transformation (FT) has been used in the theoretical line shape analysis of Franz-Keldysh oscillations (FKOs) in detail by numerical simulations. FKOs from the surface-intrinsic-n(+) GaAs structure were obtained in photoreflectance (PR) measurements with various modulation light intensities and with different strengths of bias light illumination, which were used to change the static electric field in the intrinsic layer of the sample. The FT spectra of the PR spectra, including the real part, imaginary part, and the modulus, were very consistent with the theoretical line shapes. The ratio of the square root of the reduced mass (root mu (L)/root mu (H)) and the ratio of transition strength of the electron heavy hole to the electron light hole were obtained from the PT spectra. In addition, the electric field in the intrinsic layer of the sample without and with bias illumination and the modulation field induced by photomodulation were also obtained. (C) 2000 American Institute of Physics. [S0021-8979(00)02123-X].

Fourier transformation study of the Franz-Keldysh Oscillation in SIN+ GaAs structures

Fourier transformation (FT) method has been used in the theoretical lineshape analysis of the Franz-Keldysh Oscillation (FKO) in detail by numerical simulation. The FKO of a set of GaAs SIN+ samples was obtained in photoreflectance measurements. The FT spectra of a part of the samples,including of the real part,imaginary part, and mode of the FT,are well consistent with the theoretical lineshapes. The ratio of the square root of the reduced mass of the light hole (LH) to the heavy hole (HH), root mu(1)/root mu(h), obtained in the analysis was in the range of 0.805 to 0.816 for different samples. In addition,the built-in electric field F-1, and the modulation field delta F = F-1 - F-2 induced by photo-modulation were also obtained in the analysis. However,for a few samples great difference was found in the lineshape of the real part and imaginary part of their FT spectra from the theoretical lineshape. In this case the mode of the FT spectra still can be used to obtain useful information.

Franz-Keldysh effect and dynamical Franz-Keldysh effect of cylindrical quantum wires

We investigate the interband optical absorption spectra near the band edge of a cylindrical semiconductor quantum wire in the presence of a static electric field and a terahertz electric field polarized along the axis. Optical absorption spectra are nonperturbatively calculated by solving the low-density semiconductor Bloch equations in real space and real time. The influence of the Franz-Keldysh (FK) effect and dynamical FK effect on the absorption spectrum is investigated. To highlight the physics behind the FK effect and dynamical FK effect, the spatiotemporal dynamics of the polarization wave packet are also presented. Under a reasonable static electric field, substantial and tunable absorption oscillations appear above the band gap. A terahertz field, however, will cause the Autler-Townes splitting of the main exciton peak and the emergence of multiphoton replicas. The presented results suggest that semiconductor quantum wires have potential applications in electro-optical devices.

SIN~+GaAs结构中的Franz-Keldysh振荡的傅里叶变换研究

利用傅里叶变换(FT)方法，对Franz-Keldysh振荡(FKO)的理论线性作了详细的数值模拟，并用光调制反射谱(PR)测量了一组本征层(I层)厚度不同的表面-本征层n-型重掺杂层(SIN~+)结构的GaAs样品的FKO.PR谱的FT分析表明，一部分样品的FT谱，包括其实部、虚部和模，与理论线性符合得比较好，由此求出轻空空(LH)和重空穴(HH)的约化质量平方根之比μ_1~(1/2)/(μ_h)~(1/2)对不同样品在0.805-0.816之间，同时也可以求出样品中的内建电场强度F_1，和调制光引起的调制电场δF=F_1-F_2。有一些样品的FT谱实部和虚部与理论线性差别很大，用FT的模仍可以给出有用的信息。

用Franz-Keldysh效应研究GaAs表面硫化学钝化

硫钝化是一种比较有效的钝化GaAs表面的方法。使用Na_2S、S_2Cl_2和CH_3CSNH_2三种化学试剂对表面-本征层-重掺杂层(s-i-n~+)结构的GaAs样品进行了钝化，利用光调制反射谱观察到许多个Franz-Keldysh振荡，测量出本征层的电场强度，研究了GaAs表面硫钝化前后费米能级的变化，并且比较了各种钝化方法的钝化效果。

InGaAs-GaAs短周期应变层超晶格调制反射光谱中的Franz-Keldysh振荡

在p-i-n结构的 InGaAs-GaAs应变层短周期超晶格的调制光反射谱中观察并确认了超晶格微带电子的Franz-Keldysh振荡, 通过对Franz-Keldysh振荡的分析,推算出超晶格区内建电场大小;讨论了内建电场对超晶格微带电子的影响,最后指出Franz-Keldysh振荡可以作为检验短周期超晶格样品质量的一种手段。

啁啾脉冲放大系统空间特性的优化分析

采用Franz-Nodvik模型，通过模拟计算，系统地分析了啁啾脉冲放大（CPA）过程中抽运光和信号光能量密度以及晶体参量对放大器输出能量和转换效率的影响。将理论模拟与实验结果进行比较，证明了理论分析的有效性。计算结果表明：在啁啾脉冲放大系统中，存在一个抽运光最佳能量密度。合理选择抽运光的能量密度可以有效提高系统的能量转换效率和稳定性，而且还可以大大降低系统对注入信号光能量的要求以及由于信号光能量抖动所造成的输出不稳定性。

用钛宝石再生放大器产生高重复率啁啾脉冲列

针对啁啾脉冲放大技术建成的钛宝石激光装置，提出一种获得高重复率激光脉冲列的方法．通过改变钛宝石再生放大器中泡克耳斯盒电光开关的传统工作模式，使得腔内放大的脉冲从某特定时刻起，每当在腔内往返一次就以一定的倒出比例（倒出率）倒出腔内脉冲能量的一部分，从而可以在有限的时间段内产生高重复率的啁啾激光脉冲列．基于Franz-Nodvik放大理论，建立了该高重复率再生放大器的理论模型，通过数值计算，系统地分析了初始增益、倒出时刻、倒出率对输出的脉冲序列的影响．在抽运功率为35mJ、倒出率为1／2的实验条件下，通过腔外