半导体可饱和吸收镜锁模的钒酸盐混晶Nd:Gd0.1Y0.9VO4激光器

采用Nd∶Gd_0.1Y_0.9VO₄晶体作为增益介质和Z形腔结构,分析比较了腔内加入自行设计的镀和不镀高反膜的半导体可饱和吸收镜（SESAM）对激光锁模的影响.在腔内加入镀膜SESAM后,激光锁模阈值由1.69W下降为1.45W,并且锁模更稳定.在2W抽运功率下,在1064nm中心波长处获得了双端250mW的连续锁模输出,光光转换效率为12.5%,重复频率为142.25MHz. 关键词： 0.1Y_0.9VO₄激光器')" href="#">Nd∶Gd_0.1Y_0.9VO₄激光器 半导体可饱和吸收镜 连续锁模     

Fluoride semiconductor saturable-absorber mirror for ultrashort pulse generation

We demonstrate what is to our knowledge the first ultrabroadband monolithically grown AlGaAs/CaF(2) semiconductor saturable-absorber mirror (SESAM) that covers nearly the entire gain spectrum of a Ti:sapphire laser. A large high-reflectivity bandwidth of more than 300 nm is provided by a device consisting of only six material layers. This fluoride SESAM had a modulation depth of 2.2%, a fast recovery time constant of less than 150 fs, and a slow recovery time constant of 1.2 ps. Using this SESAM inside a Ti:sapphire laser produced self-starting sub-10-femtosecond pulses.     

Optical characteristics of semiconductor saturable absorber mirrors investigated by the reflection Z-scan technique

Recently, the semiconductor saturable absorber mirror (SESAM) has become a key component of passive mode-locked solid-state lasers. Here we present a simple method based on the reflection Z-scan technique to measure the key optical parameters of SESAM such as saturation fluence and modulation depth. The experimental results demonstrate that our method is able to perform with a high accuracy of 10⁻⁴ and a dynamic range of over four orders of magnitude.     

用于钛宝石激光器自启动锁模的半导体可饱和吸收镜

报道国内首次制作的宽带低损耗半导体可饱和吸收镜（SESAM）。该反射镜已经成功用于钛宝石飞秒脉冲激光器的自启动锁模运转。     

Ultrafast Nonlinear Optical Properties of a Graphene Saturable Mirror in the 2 μm Wavelength Region

Mid‐infrared ultrafast lasers have emerged as a promising platform for both science and industry because of their inherent high raw power and eye‐safe spectrum. 2D nanostructures such as graphene have emerged as promising photonic materials for laser mode‐locking to generate ultrashort pulses. However, there are still many unanswered questions about graphene's key advantages to be practical devices, especially over the matured semiconductor saturable absorber mirror (SESAM). In this work, we conducted systematic comparisons on the nonlinear optical properties of graphene and that of a commercial SESAM at 2 μm wavelength. Our results showed that graphene has significant advantages over the commercial SESAM, exhibiting ∼28% less absorptive cross‐section ratio of excited‐state to ground‐state and ∼50 times faster relaxation time. This implies that graphene can be exploited as a better mode‐locker than the current commercial SESAM for high power, high repetition rate and ultrafast mid‐infrared laser sources.     

含负克尔效应半导体可饱和吸收镜的五镜腔飞秒钛宝石激光器的理论分析

基于半导体可饱和吸收镜(SESAM)的负克尔效应，对含SESAM的五镜腔进行了理论计算和分析.结果表明，由于SESAM的负克尔效应，与没有SESAM的相比，锁模激光器的稳区在上稳区的内边缘有明显扩展，这使得激光器锁模启动的工作点更加靠近直流运转时的稳区边缘，从而获得更大的非线性因子.这说明SESAM的可饱和吸收机理具有锁模自启动效应外，其负克尔效应也有助于锁模的自启动. 关键词： 半导体可饱和吸收镜 负克尔效应 五镜腔     

Semiconductor saturable absorber mirror structures with low saturation fluence

We present two novel semiconductor saturable absorber mirror (SESAM) designs which can exhibit more than ten times lower saturation fluence than classical SESAM devices. Design considerations and characterization data are presented. These devices are particularly suited for passively mode-locked lasers with ultra-high repetition rates.     

Adjustable picosecond pulse duration in a LD end pumped SESAM passively mode-locked Nd:YVO<Subscript>4</Subscript> laser

With adjustable pulse durations, a semiconductor saturable absorber mirror (SESAM) passively mode-locked picosecond Nd:YVO₄ laser was studied. The pulse duration was adjustable from 20 to 80 ps by using intracavity etalons of different thicknesses.     

电场调控双层石墨烯纳米带的电子结构和光学性质

利用基于密度泛函理论的第一性原理方法,研究了外加电场作用下双层AA堆垛的Armchair边缘石墨烯纳米带(BAGNRs)的电子结构和光学性质. BAGNRs具有半导体特性,其带隙随带宽(宽度为4～12个碳原子)的增加而振荡性减小.当施加电场后,BAGNRs的带隙随着电场强度的增加而逐渐减小,带隙越大对电场值的变化越敏感.当电场值为0.5 V/?时,所有BAGNRs的带隙都为零. BAGNRs具有各向异性的光学性质,其介电函数在垂直极化方向为半导体特性,而在平行极化方向为金属特性.在外加电场的作用下,BAGNRs的介电函数、吸收系数、折射系数、反射系数、电子能量损失系数和光电导率,其峰值向低能量区域移动,即产生红移现象.电场增强了能带间的跃迁几率.纳米带宽度对这些光学性质参数具有不同程度的影响.研究结果解释了电场调控BAGNRs光学性质的规律和微观机理.     

Passively mode-locked fiber ring laser using semiconductor saturable absorber mirror

We experimentally demonstrate a fiber laser passively mode-locked by a semiconductor saturable absorber mirror (SESAM) in a ring cavity. A pulse series with a temporal width of 1 ns is generated at a repetition rate of 12.3 MHz. With careful polarization adjustment, the pulse width decreases, the peak power increases and the spectral sidebands are formed in the optical spectrum. The reason of the phenomenon above has been analyzed. In addition, the characteristic of the pulse with different length of the Er³⁺ Doped Fiber (EDF) is studied and the results show that it is reabsorption that causes the laser to shift to longer wavelength direction when the EDF length increases.     

Time division vector optical sampling for ultrafast amplitude/phase modulation device characterization

A technique is proposed and demonstrated for measuring the waveforms of optical signals by making use of homodyne in-phase and quadrature detection combined with nonlinear optical sampling. The technique is based on time division sampling of electric field components with a discretely phase-modulated local oscillator light and is applied for the evaluation of the ultrafast response in a semiconductor optical amplifier.     

Thermal effects investigation and cavity design in passively mode-locked Nd:YVO4 laser with a SESAM

A diode-pumped passively mode-locked Nd:YVO₄ laser with a five-mirror folded cavity is presented by using a semiconductor saturable absorber mirror (SESAM). The temperature distribution and thermal lensing in laser medium are numerically analyzed to design a special cavity which can keep the power density on SESAM under its damage threshold. Both the Q-switched and continuous-wave mode-locked operation are experimentally realized. The maximum average output power of 8.94 W with a 9.3 ps pulse width at a repetition rate of 111 MHz is obtained under a pump power of 24 W, correspondingly the optical slope efficiency is 39.2%.     

Broadband semiconductor saturable-absorber mirror for a self-starting mode-locked Cr:forsterite laser

We report a low-loss broadband semiconductor saturable-absorber mirror (SESAM) that uses gold film as the reflector. A semiconductor- SiO(2) double-layer stack enhances the reflectivity of the gold film. This low-loss SESAM was used in a mode-locked Cr:forsterite laser to produce self-starting 20-fs-scale laser pulses at 1.3 microm . The structure can be applied to SESAM's for other wavelengths.     

Passively modelocked surface-emitting semiconductor lasers

This paper will review and discuss pico- and femtosecond pulse generation from passively modelocked vertical–external-cavity surface-emitting semiconductor lasers (VECSELs). We shall discuss the physical principles of ultrashort pulse generation in these lasers, considering in turn the role played by the semiconductor quantum well gain structure, and the saturable absorber. The paper will analyze the fundamental performance limits of these devices, and review the results that have been demonstrated to date. Different types of semiconductor saturable absorber mirror (SESAM) design, and their characteristic dynamics, are described in detail; exploring the ultimate goal of moving to a wafer integration approach, in which the SESAM is integrated into the VECSEL structure with tremendous gain in capability. In particular, the contrast between VECSELs and diode-pumped solid-state lasers and edge-emitting diode lasers will be discussed. Optically pumped VECSELs have led to an improvement by more than two orders of magnitude to date in the average output power achievable from a passively modelocked ultrafast semiconductor laser.     

Low-threshold diode-pumped CW passively mode-locked Nd:YVO4 laser

A low-threshold passively continuous-wave (CW) mode-locked Nd:YVO₄ solid-state laser was demonstrated by use of a semiconductor saturable absorber mirror (SESAM). The threshold for continuous-wave mode-locked is relatively low, about 2.15 W. The maximum average output power was 2.12 W and the optical to optical conversion efficiency was about 32%. The pulse width was about 15 ps with the repetition rate of 105 MHz.     

Optical Conductivity of Impurity-Doped Parabolic Quantum Wells in an Applied Electric Field

The optical conductivity of impurity-doped parabolic quantum wells in an applied electric field is investigated with the memory-function approach, and the analytic expression for the optical conductivity is derived. With characteristic parameters pertaining to GaAs/Ga_1-xAl_xAs parabolic quantum wells, the numerical results are presented. It is shown that, the smaller the well width, the larger the peak intensity of the optical conductivity, and the more asymmetric the shape of the optical conductivity; the optical conductivity is more sensitive to the electric field, the electric field enhances the optical conductivity; when the dimension of the quantum well increases, the optical conductivity increases until it reaches a maximum value, and then decreases.     

半导体可饱和吸收镜启动克尔透镜锁模机理的实验研究

对采用腔内新型宽带半导体可饱和吸收镜(SESAM)掺钛蓝宝石激光器中的启动克尔透镜锁摸(KLM)的机理进行了实验研究.讨论了SESAM在阻挡恢复过程中,启动锁模时间与其他因素的关系.获得了SESAM启动KLM过程较为完整的物理图像,并对其机理进行了分析和讨论.     

正对电极结构碳化硅光导开关的电路模型

利用SilvacoTCAD软件,在532 nm激光辐照下,对正对电极结构6H-SiC光导开关（SiC-PCSS）瞬态电流电场的分布及不同光功率下的伏安特性进行了仿真。结果表明:载流子速率在强场下达到饱和,并且电流电场在主要电流区域沿垂直于激光辐照方向均匀分布。提出SiC-PCSS电路模型的建模依据,可以近似条件化简得到PCSS电阻一般表达式的解,建立SiC-PCSS载流子迁移率随电场变化的PSpice模型,分析讨论了外电路参数对SiC-PCSS导通过程的影响。该模型模拟结果与已有实验结果吻合良好。     

半导体可饱和吸收镜被动锁模侧面抽运Nd:YAG激光器研究

利用半导体可饱和吸收镜(SESAM)锁模技术实现的超快脉冲激光器具有结构简单紧凑、脉冲序列稳定等优势,在许多领域有着重要用途,自问世以来受到国内外的广泛关注.分析了SESAM被动锁模侧面抽运固体激光器的具体要求,进行了不同条件下的SESAM被动锁模侧面抽运Nd:YAG激光器实验.获得了最高平均功率9.5 W,脉冲重复频率71 MHz,单脉冲能量约141 nJ的皮秒激光脉冲.对SESAM被动锁模侧面抽运Nd:YAG激光器进行了实验和理论分析,对实现高功率连续超短脉冲激光器进行了探讨.     

Compact 10-GHz Nd:GdVO4 laser with 0.5-W average output power and low timing jitter

We demonstrate a compact, diode-pumped Nd:GdVO4 laser with a repetition rate of 9.66 GHz and 0.5-W average output power. The laser is passively mode locked with a semiconductor saturable absorber mirror (SESAM), yielding 12-ps-long sech2-shaped pulses. For synchronization of the pulse train to an external reference clock, the SESAM is mounted on a piezoelectric transducer. With an electronic feedback loop of only a few kilohertz loop bandwidth we achieved a rms timing jitter of 146 fs (integrated from 10 Hz to 10 MHz). This is an upper limit because it is mostly limited by the measurement system. The laser setup with a simple linear cavity has a footprint of only 130 mm x 30 mm.