高稳定连续Nd：YAG锁模激光器脉宽的测试

本文简略地介绍锁模激光脉宽的一般测量。文章重点讨论并用光电法及二次谐波法实测了高稳定连续Nd：YAG锁模激光器的脉宽。     

倍频晶体β-BaB_2O_4在锁模Ar~+激光脉冲相关测量中的应用

β-BaB_2O_4(偏硼酸钡)晶体是我国首先发现和生长的新型倍频晶体。我们将此晶体应用于锁模Ar~+激光脉冲的自相关测量中(即二次谐波方法),在室温下,很方便地测出了我们的锁模Ar离子激光器输出的脉冲宽度约为190ps与以前采用过的低温法及互相关法得到的结     

同步抽运锁模的掺镱光纤激光器

同步抽运锁模是一种调制增益的锁模技术，就是调节抽运光的调制频率使之等于激光器纵模间隔的整数倍。通过对抽运光源半导体激光器的驱动电流进行正弦调制，实现了掺镱光纤激光器(YDFL)的同步抽运锁模。通过调整抽运激光器的调制频率，在相应于二次谐波锁模，4阶有理数谐波锁模条件下分别得到了较窄的脉冲输出。对重复频率625kHz的二次谐波锁模脉冲序列，脉冲宽度小于20ns，约为抽运光宽度的1／40；平均输出功率2．34mw，能量转换效率约为5％。     

一种新型的实时显示二次谐波相关仪

本文提出了一种测量飞秒(10~(-15)s)光脉冲脉宽的实时显示二次谐波相关仪,并对读仪器进行了系统的实验研究,已用它作为碰撞脉冲锁模(CPM)环形染料激光器脉宽的监测仪。     

光栅—克尔光闸—摄象选行示波超短光脉冲实时测试系统

本文分析了光栅—克尔光闸—摄象选行示波超短光脉冲测试系统的工作原理,实验测量了锁模 YAG 激光器的二次谐波和同步泵浦染料激光器的输出脉宽。     

稳定的锁模Nd:YAG激光器

本专利叙述了通过反馈回路控制激光腔长使锁模Nd:YAG激光脉冲振幅及重复率达到稳定的方法与装置。激光器终端反射镜安装在以低频振动的压电晶体上,激光辐射的一部分1.06微米基波转换成二次谐波频率,二次谐波频率的平均功率被积分检波器接收,二次谐波功率的大小决定于激光腔光学长度与锁模频率之间的匹配。腔长由反馈回路进行控制,该回路对二次谐波探测器的输出和压电晶体的振动信号进行比较。     

全光纤掺镱激光器实现锁模和多波长输出

利用半导体可饱和吸收镜(SESAM)和光纤环形镜(FLM)分别作为腔镜,实现了线形腔结构的全光纤掺镱激光器.通过调节偏振控制器(PC)和抽运功率得到了调Q、调Q锁模、连续锁模、二次谐波、三次谐波、多波长等多种输出状态.其中连续锁模状态可实现开机自启动,脉冲宽度31 ps,单脉冲能量40 pJ,重复频率19.3 MHz,...     

石墨烯被动锁模谐波阶数可调的掺铒光纤孤子激光器

采用石墨烯被动锁模的掺Er光纤(EDF)环形腔,获得稳定的谐波阶数可调的孤子脉冲激光。通过调节EDF环形腔中的偏振控制器(PC)改变光腔损耗,实现了锁模谐波从一阶至四阶的可控运转。连续锁模基频重复频率为3.873MHz,中心波长为1 557.6nm,谱线宽度为4.5nm,有明显孤子边带,信噪比(SNR)约为45dB,二、三和四次谐波锁模脉冲重复频率分别为7.745、11.618和15.491MHz。本文的实验结果可用工作于反常色散区锁模激光器的多孤子形成机理来解释。     

一种新型的锁模脉冲YAG激光器

本文介绍一种新型的锁模脉冲YAG激光器。其结构简单、性能稳定、可靠,可高重复频率、长时间运转。在长脉冲泵浦的多掺杂YAG激光器的谐振腔内,介入一声光损耗调制器,无需引入任何其它附加的光学元件,便可实现稳定可靠的锁模。其工作波长为1.064μm,锁模脉冲序列包络总能量为4～8mj,锁模脉冲间隔为5ns,每列脉冲内含11个锁模脉冲。用共线二次谐波法测量,锁模脉冲的半宽度约为250ps。锁模脉冲幅值稳定度≥15％,锁模几率100％,输出光束为TEM_(00)模,并且是偏振的,光束发散角小于0.8mrad。     

高次谐波锁模飞秒掺镱光纤激光器的噪声情况

高重复频率的飞秒激光在高速激光测距和三维成像等领域有着非常重要的作用。其中基于飞秒光纤激光器的高次谐波锁模是获得GHz量级以上高重复频率脉冲的重要手段之一。基于含腔内光栅对色散补偿的非线性偏振旋转（NPR）锁模的掺镱（Yb）光纤激光器,在180 mW泵浦光时获得了稳定的143 MHz基频锁模脉冲序列,当泵浦光功率升至1 W时获得了最高20次谐波（2.86 GHz）锁模脉冲序列输出。系统地对比研究了基频锁模与高次谐锁模状态下,脉冲重复频率精密锁定后的艾伦偏差和相位噪声,7次谐波锁模状态下重复频率锁定精度能够保持在10?13 Hz@1 s的稳定度,为高次谐波锁模飞秒激光脉冲序列用于精密测量提供了实验依据。     

Generation of picosecond optical pulses with highly RF modulated AlGaAs DH laser

AlGaAs DH lasers with strong RF modulation superimposed on the relatively low dc bias below the oscillation threshold were demonstrated to be feasible for generation of a train of approximately 30 ps optical pulses at a repetitive frequency of sub-GHz range. The pulse envelope width was measured by three different methods: a fast response photodetector, the second-harmonic generation (SHG) correlation method, and an ultrafast streak camera. The results of the SHG correlation and the streak camera agreed fairly well. In order to explain the generation mechanism and the characteristics of these ultrashort optical pulses in a highly RF modulated semiconductor diode laser, the rate equation analysis was performed and the results were generally in good agreement with the experiment. Furthermore, from the computer simulation for the analysis of the SHG correlation traces, it was inferred that an individual ultrashort optical pulse has internal substructures made of fluctuating fields whose spike widths were of the order of subpicoseconds, due to the randomness of the phases among lasing modes.     

Theoretical analysis of squeezed-light generation bysecond-harmonic generation

Theoretical analysis of squeezed light generation by phasematched SHG, applicable generally to various SHG configurations and appropriate for mutual comparison, is presented. The analysis is based on analytical solutions of the linearized differential equations in space coordinate and the input-output equations for the amplitude fluctuations, and calculations of squeezing spectra using the covariance matrixes. Formulations describing the squeezing characteristics in terms of the device parameters are derived. Typical numerical results are also given to illustrate the features of traveling-wave SHG, singly-resonant SHG, and doubly-resonant SHG configurations including cases where propagation losses are involved. The results, which are consistent with those in previous work, provide many insights for design and application of SHG devices for squeezed-light generation     

变反射率镜耦合输出的高效率倍频Nd:YAG激光器的研究

采用合适的参数,使变反射率镜耦合输出的非稳定腔Nd:YAG脉冲激光器的倍频效率获得显著提高。当用KTP或DKDP晶体倍频时,倍频光的输出能量分别高达440mJ或300mJ每脉冲,倍频效率分别为60％和40％,光束发散角约为0.38mrad,接近衍射极限。     

Observation of second-harmonic generation from a Langmuir-Blodgett monolayer of a merocyanine dye

Second-harmonic generation (SHG) from a merocyanine dye Langmuir-Blodgett monolayer is reported. Values for the second-order molecular polarisability ? and its average orientation within the layer are deduced. Extinction of the SHG is observed for symmetrical bilayers. Protonation of a dye monolayer is seen to suppress SHG.     

Broadening of the phase-matching bandwidth in quasi-phase-matchedsecond-harmonic generation

We report on theoretical analysis and experiments for bandwidth broadening in quasi-phase-matched (QPM) second-harmonic generation (SHG) in LiTaO₃. QPM waveguides consisting of segments, where each segment has a phase-matching condition different from the others, are proposed to obtain a broad bandwidth and simultaneously, a high SHG efficiency. The waveguides were fabricated by adjusting the phase-matching condition either by changing the grating period of the SHG coefficient or by controlling the width of the waveguide. Consequently, the bandwidth of QPM-SHG was broadened to 0.35 nm with an SHG efficiency of 57 percent/W by modulation of the waveguide width and to 1.12 nm with an SHG efficiency of 29 percent/W by modulation of the grating period. The SHG efficiency and phase-matching characteristics in both types of waveguides showed good agreement with theoretical results     

Theoretical analysis of resonant waveguide optical second harmonicgeneration devices

Theoretical analysis of resonant waveguide SHG devices is presented. Mathematical expressions for SHG interaction in waveguides for arbitrary initial conditions were derived and applied to the analysis. Dependences of SHG efficiency on pump amplitude of singly and doubly resonant devices with various cavity mirror reflectivities, phase-mismatch, and propagation losses are compared with that of traveling-wave devices. It is shown that in resonant SHG devices much higher efficiency is obtained for low pumping power than in traveling-wave device. It is found, for the first time, that complete conversion can be attained for a finite input power in the doubly resonant devices. However, the efficiency is very sensitive to the propagation losses     

二次谐波细胞成像的研究进展

由于二次谐波(Second harmonic generation, SHG)技术具有探测深度深,对生物体的损伤小,时间空间分辨率高以及对结构的对称性敏感等特性,SHG成像成为近年来生物成像领域的研究热点.介绍了SHG成像技术的原理及其在细胞成像中的应用,重点介绍了基于染料标记的成像技术,特别是利用电压敏感染料,手性材料和金属纳米粒子作为标记的几种SHG细胞成像技术,最后展望了该技术在生物成像领域的应用前景.     

Induced second-harmonic generation in planar waveguides by anexternally applied periodic DC electric field: efficiency as a functionof field structure

The efficiency of second-harmonic generation (SHG) induced by an externally applied periodic DC electric field was investigated. A finite element method was used to find the static electric field due to different interdigitated electrode structures. The resulting fields were used to calculate the overlap integrals which determine the SHG efficiency in an optical waveguide. The results show that there are reasonable differences in SHG efficiencies for the structures investigated     

The First Improper Ferroelectric of 2D Multilayered Hybrid Perovskite Enabling Strong Tunable Polarization-Directed Second Harmonic Generation Effect

2D organometallic halide perovskites are recently emerging as a robust family of ferroelectrics, of which their inherent spontaneous polarization (P_s) endows fascinating quadratic nonlinear optical properties. However, up to date, few studies are reported to tune and control the second harmonic generation (SHG) effect in this ferroelectric branch. Herein, the first improper ferroelectric of 2D multilayered hybrid perovskites, (IA)₂(EA)₂Pb₃Br₁₀ ( 1 , where IA is isoamylammonium and EA is ethylammonium), which exhibits a high Curie temperature ( ≈ 371 K) and biaxial ferroelectricity with P_s of 2.2  µ C cm⁻² is reported. Strikingly, its unique in-plane ferroelectricity allows strong tunable SHG properties under the polarized-light. That is, the maximum SHG signals are observed with polarized-light parallel to P_s, while the minimum SHG appears along the vertical direction. This SHG anisotropy creates an extremely large dichroism ratio of ≈ 12, as visualized by 2D color mapping, which is the record-high merit for this type of SHG systems. To the best knowledge, this is the first time to achieve tunable SHG effects through ferroelectric polarization. As a pioneering study, the coupling between the SHG effect and ferroelectricity paves a new direction of 2D hybrid perovskite ferroelectrics toward smart optical device applications.     

Local normal-mode analysis of second harmonic generation in aperiodic waveguide

A new theoretical analysis method based on the local normal-mode expansion is proposed for analysis of optical second harmonic generation (SHG) under quasi-phase-matching in a waveguide with a periodic structure. Nonlinear coupled mode equations, SHG efficiency, and effective SHG coefficient are derived. In addition, SHG devices quasi-phase-matched with corrugation and with periodic domain inversion are studied analytically and numerically. The results are compared to those obtained by the conventional ideal normal-mode expansion. It is shown that in a corrugated waveguide the local normal-mode expansion method presents a different result from the ideal normal-mode expansion since the periodic variation of the modal field profile is dominant in the quasi-phase-matching process. On the other hand, in the periodically domain-inverted ferroelectric waveguide, it is shown that the variation of the modal field profile is sufficiently small and both expansion methods coincide with each other