碰撞锁模多量子阱半导体激光器模式锁定过程的物理模型

提出了碰撞锁模多量子阱激光器模式锁定过程的完整的物理模型，该模型全面地考虑了吸收体的饱和吸收效应和瞬态光栅效应及增益区端面附近和靠近吸收体处的瞬态光栅作用。作为应用实例采用本模型研究了多量子阱结构激光器的模式锁定过程及瞬态光栅对脉冲半峰宽及峰值功率的影响。     

激光对撞锁模技术的物理模型研究

本文深入讨论了脉冲对撞锁模(CPM)技术中,两脉冲在可饱和吸收体内对撞的过程,建立了描述此过程的物理图像,并由此得出了关于脉冲对撞锁模物理机制的简明而清晰的新解释。     

双稳外腔半导体激光器(ECLD)模式转换的数值描述

对多模半导体激光器(LD)的速率方程组进行了数值求解,分析了光栅双稳外腔半导体激光器(ECLD)模式发生跳变时的瞬态特性,讨论了光栅转角的大小对瞬态过程的影响。结果表明,当光栅转角较小时,ECLD在功率上跳过程中,切断模(switch offmode)在熄灭前可能会产生一个窄而强的光脉冲。这一现象在下跳过程中是不存在的。且上跳时,ECLD更快地达到稳态输出。     

准共线声光可调谐掺铒光纤激光器的研究

提出了一种新颖的单纵模、单偏振的可调谐掺铒光纤激光器结构。使用准共线型声光可调谐滤波器作为调谐元件。利用饱和吸收效应在未泵浦低掺铒光纤中形成自写入瞬态光栅,用以压窄输出激光的线宽,并且有效地防止跳模。理论计算表明:当泵浦功率为100mW时,激光器的输出功率可达5.5mW,输出线宽在10-4nm量级。这些数据对后续的实验研究有指导作用。     

CPM染料激光器与飞秒光脉冲技术

染料激光器有较宽的增益带宽,因此能产生很窄的锁模脉冲。1972年Ippen等人利用DODCI作为饱和吸收体实现对Rh6G连续染料激光器的被动锁模,获得1.5皮秒的脉冲宽度。后1981年Fork等人实现了环形染料激光器的脉冲碰撞锁模,他们利用两个相反方向的光脉冲在可饱和吸收体内相遇其相干叠加在吸收体内形成粒子数分布光栅的作用,     

啁啾光纤光栅中偏振模色散的研究

首先介绍了不同种双折射率差Δn的光纤制成的啁啾光纤光栅中偏振模色散现象 ,然后说明了光栅中偏振模色散的大小与 Δ n的相关性 ,并阐述了对用于色散补偿作用的啁啾光纤光栅中偏振模色散的消除 (补偿 )方法 ,最后指出利用啁啾光纤光栅中大的偏振模色散对高速光通信系统传输线路中偏振模色散的补偿方法。     

用于Nd:YAG对撞锁模激光器的腔型分析

本文对用于Nd:YAG对撞锁模激光器的三种带非共振环腔进行了分析,较祥细的讨论了腔参数的选择和象散等问题。并对这种腔型各自的特点和优劣进行了具体的分析比较。     

碰撞锁模环形腔稳定性区域的理论和数值分析

对碰撞锁模实验中所用六镜环形腔的稳定性区域进行了理论分析,利用3:1关系得到了极其简明的解析解。在对稳定区域面积随腔参数变化进行的数值计算基础上,提出了一种提     

V-I传输矩阵方法在布拉格光纤光栅分析中的运用

介绍了V-I传输矩阵方法用于布拉格光纤光栅的理论分析,该方法通过参量变换将相邻薄层间的界面矩阵退化为单位矩阵,从而大大提高了计算效率。从传输矩阵出发,数学上推导出耦合模方程,证明了该方法的正确性,有助于加深对V-I传输矩阵方法物理机制的理解。数值模拟分析发现V-I传输矩阵方法具有计算快速、简单明了的优点。最后还指出V-I传输矩阵方法仅适用于短周期光纤光栅,若要运用于长周期光纤光栅,需要进一步理论修正。     

无透镜瞬态光栅外差检测光学技术

光学检测中的瞬态光栅法被材料学家们用于测量和观察分子和晶格振动、声波、热散射、分子散射以及其它一些有趣的现象。在瞬时光栅外差检测法中,激光束被一个普通相位板一分为二:泵浦光和探测光。泵浦光在检测样品中干涉形成光栅,探测光则在样品中衍射,所产生的强度决定物理数据。但是在过去,这种仪器要求很高精度的光准直,这个方法根本不可能普遍使用。东京大学的研究人员开发了一种简易式瞬态光栅方法,使得这一检测技术更便于使用。在这套无透镜系统中,泵浦光和探测光通过一个二色镜合二为一,然后一起入射到透射光栅,从而在样品中形成干涉,探测光同时被透射光栅和瞬态光栅衍射,两束衍射光一起被检测到。     

Dynamics of monolithic passively mode-locked semiconductor lasers

Monolithic colliding pulse mode-locking (CPM) in semiconductor lasers is compared with self colliding pulse mode-locking (SCPM) through a large signal dynamic computer model which incorporates most of the significant features of semiconductor lasers. These include gain saturation, spontaneous emission, the gain-frequency relation, and the line-width enhancement factor. This new model replicates many of the published experimental results and also gives additional insight into the internal operation of the device. In particular, gain saturation combined with the standing waves created by colliding pulses within the saturable absorber produce a transient gain grating. This is found to have significant effects in locking either the even or the odd modes together in CPM. A performance comparison between CPM and SCPM is completed and some key design parameters of both configurations are explored     

Calculation of the colliding pulse mode locking in CW dye ring lasers

A calculation of the influence of a transient absorber grating on the pulse parameters of a dye laser in the "colliding pulse mode-locking" (CPM) regime is given. It is shown that, compared to other passive methods, considerably shorter pulses with a more favorable stability region can be obtained. Within the stability range of single pulse operation the shortest pulses in the CPM are obtained by operating far above threshold where the saturation energy of the amplifier is much greater than that of the absorber. Deviation from an amplifier position that is symmetric with respect to the amplification of the counter-running pulses leads to different energies of the pulses and to a strong decrease of the stability range. Taking the dispersive properties of absorber and amplifier into consideration, equations for the time dependent phase of the laser pulse are established and solved by an analytical ansatz. The resulting pulse chirp is shown to be mainly dependent on the detuning of the pulse frequency from the center frequency of the saturable absorber. The estimated values for the pulse duration and the down-chirp for typical experimental conditions of a rhodamine 6G-DODCI CPM laser agree well with the measured ones.     

Dynamics of laser annealing of amorphous Ge and GaAs films by the transient grating method

The transient grating method has been applied to study both heating and crystallization dynamics of amorphous Ge and GaAs films in the nanosecond time scale. The observed time behavior of the diffracted signals allows measurements of the onset of melting and of the full solidification time. From the model Calculations, we show that the free-carrier diffusion is a predominant process in laser heating under high excitation power and leads to the saturation of carrier density before melting. The heating of amorphous Ge in a limited volume gives evidence of a decrease in melting temperature.     

Picosecond photorefractive and free-carrier transient energytransfer in GaAs at 1 μm

The strength, formation, and decay of photorefractive and free-carrier gratings written in GaAs by 43-ps pulses at a wavelength of 1 μm are investigated using picosecond-time-resolved two-beam coupling, transient grating, and degenerate-four-wave-mixing techniques. Photorefractive weak-beam gains of a few percent are measured at fluences of a few pJ/μm² (0.1 mJ/cm²), and gain from transient energy transfer is observed at fluences larger than ~10 mJ/cm² in the beam-coupling experiments. The roles of saturation and two-photon absorption in determining the final electron, hole, and ionized-donor populations and the roles of drift and diffusion in determining the quasi-steady-state photorefractive and free-carrier index modulations are discussed     

Study of the dynamics of excited states in CdS and CuCl by transient grating techniques

Transient grating measurements on sample with an anisotropy or with multiple excited states are described. The general formula for the intensity of the diffracted light from a transient grating in a sample with an anisotropic diffusion coefficient is presented and is applied to CdS. A transient grating spectroscopic technique for a sample with multiple excited states is discussed in detail. In addition to these, the contribution of a population and a thermal grating to the observed signals is discussed.     

New grating experiments in the study of irreversible photochemical reactions

We have investigated the irreversible hydrogen abstraction of benzophenone in glassy polymers through holographic grating techniques. Recording the decay of the transient grating after pulsed excitation and the building up of a permanent grating during CW excitation allows the extraction of valuable information about the photochemical kinetics. Variation of the fringe spacing permits one to distinguish diffusive and reactive processes, and so transient grating experiments promise to be of great value in the study of diffusion-controlled reactions. As grating experiments are sensitive to changes in the absorption coefficient as well as the index of refraction, one can very sensitively detect density changes and deformations of the matrix which accompany the photochemical transformation in the sample.     

Saturation of self-prepared frequency doubling fibres

The saturation in self-prepared frequency doubling fibres was studied. A numerical model was implemented to predict the width and position of the grating. A comparison with experiments showed that self-erasure dominates saturation     

Modeling and experimental demonstration of ultracompact multiwavelength distributed Fabry-Pe/spl acute/rot fiber lasers

This work presents a complete model for the design and optimization of multiwavelength distributed Fabry-Pe/spl acute/rot (DFP) fiber lasers that are made by superimposing two chirped fiber Bragg gratings in a photosensitive codoped erbium-ytterbium (Er-Yb) fiber. The model is based on a matrix formulation of coupled-mode equations taking into account the chirped grating superstructure and including a spectrally resolved gain medium. The performed analysis reveals that the signal power of each channel is strongly localized near a minimum of the superstructured-grating envelope. As a consequence, the overlap between the power distributions in neighboring cavities is small, thus reducing the effect of cross-gain saturation and allowing a high number of channels in a short piece of fiber. The simulations also show how the saturation of the cross-relaxation mechanism between ytterbium and erbium leads to flat output spectra without the need for an additional equalization scheme such as a complex grating apodization profile. Furthermore, to validate the theoretical model, we present the experimental realization and characterization of a multiwavelength laser emitting in a single-mode and single-polarization over 16 wavelengths spaced by 50 GHz and with a total output power of 52 mW.     

A physical model for mode-locking process of colliding pulsemode-locked multiquantum-well semiconductor laser

In this paper, we first present a physical model for mode-locking process of the colliding pulse mode-locked multiquantum-well laser diode (CPM-MQW-LD). The absorption of saturable absorber on pulse leading edge and the scattering of the transient grating generated in absorption and gain regions on pulse trailing edge are considered. As an example, the mode-locking process of a multiquantum-well structure laser and the effect of transient grating on pulse width and peak power are studied