非单色光抽运的光参量啁啾脉冲放大的带宽及增益特性研究

采用傅里叶变换的方法将脉冲光分解成不同的频率成分,建立了非单色光抽运的光参量放大耦合方程组的数值求解模型.研究了非单色抽运光对光参量啁啾脉冲放大的小信号增益、大信号增益以及增益带宽的影响.非单色抽运光降低参量放大的增益水平,但同时可提高增益带宽,且抽运光谱宽越宽,对增益带宽的提高作用越大.还进一步从相位失配和参量带宽的角度分析了非单色抽运光使参量放大的增益降低、带宽增大的原因. 关键词： 光参量啁啾脉冲放大 非单色光 增益带宽 飞秒激光     

Design of high-efficiency diffraction gratings based on total internal reflection for pulse compressor

We present designs of high-efficiency compression grating based on total internal reflection (TIR) for picosecond pulse laser at 1053 nm. The setup is devised by directly etching gratings into the bottom side of a prism so that light can successfully enter (or exit) the compression grating. Dependence of the −1 order diffraction efficiencies on the constructive parameters is analyzed for TE- and TM-polarized incident light at Littrow angle by using Fourier modal method in order to obtain optimal grating structure. The electric field enhancement within the high-efficiency TIR gratings is regarded as another criterion to optimize the structure of the TIR gratings. With the criterion of high diffraction efficiency, low electric field enhancement and sufficient manufacturing latitude, TIR compression gratings with optimized constructive parameters are obtained for TE- and TM-polarized incident light, respectively. The grating for TE-polarized light exhibits diffraction efficiencies higher than 0.95 within 23 nm bandwidth and relatively low square of electric field enhancement ratio of 5.7. Regardless of the internal electric field enhancement, the grating for TM-polarized light provides diffraction efficiencies higher than 0.95 within 42 nm bandwidth. With compact structure, such TIR compression gratings made solely of fused silica should be of great interest for application to chirped pulse amplification (CPA) systems.     

超声阵列的多频脉冲压缩方法研究

脉冲压缩方法通过采用编码信号激励与脉冲压缩接收来提高超声检测的时间分辨率和信噪比。然而,受换能器带宽的限制,编码信号的时间带宽积往往有限,影响脉冲压缩效果。开展了基于超声阵列的多频脉冲压缩方法研究,超声阵列是由具有不同中心频率和带宽的多个阵元组成,从而使得整个阵列具有比单个换能器更宽的带宽。提出了压缩后叠加取包络的脉冲压缩方法,并研究了这种方法在提高时间分辨率和主副瓣比上的技术方案,对多频脉冲压缩的超声阵列进行了设计与优化,发现多频脉冲压缩方法能很大程度地提高时间分辨率,并能有效地抑制各阵元信号叠加产生的周期副瓣。理论和实验结果表明,这种压缩后叠加取包络的方法得到的时间分辨率在性能上受阵元带内不平整度的影响很小,能使阵元压缩包络中的主副瓣比得到明显改善。      

Dynamics of high-power self-similar light pulses in a fiber laser with a carbon-nanotube saturable absorber

We present a numerical analysis of the dynamics of high-power self-similar light pulses in a fiber laser with a saturable absorber based on carbon nanotubes (CNTs). This analysis allows us to identify lasing regimes in a CNT-mode-locked ytterbium-fiber laser enabling the generation of self-similar linearly chirped light pulses with an energy up to 330 nJ, which can be compressed to a 210-fs transform-limited pulse width through linear chirp compensation in a pulse compressor. We show that, for typical parameters of a fiber laser, the bandwidth and the minimum transform-limited pulse width of a self-similar laser output are primarily limited by the small modulation depth of a CNT absorber.     

Second-harmonic generation with traveling-wave pulses

We experimentally studied properties of traveling-wave excitation and traveling-wave pulse compression for a Nd : glass laser system with a streak camera. These properties were extended to second-harmonic generation with a type-11 KDP crystal. We found that the second-harmonic pulse generated from the chirped-fundamental pulse also has a good chirp linearity, but the spectral bandwidth and temporal duration were reduced. We demonstrated the effective subpulse suppression in the compressed pulse with the second-harmonic generation. The pulse with tilted wave front, short wavelength and high contrast ratio can be obtained by the second-harmonic generation of traveling-wave pulse.     

基于互逆光纤色散的微波光子雷达系统设计和实现

提出一种基于互逆光纤色散的微波光子雷达系统设计方案,既可以产生宽带线性调频信号,又可以实现线性调频信号的光域脉冲压缩.在发射端利用互逆色散光纤产生线性调频信号.在接收端,雷达回波信号通过马赫-曾德调制器调制到预啁啾的光信号上,然后经过色散光纤的进一步色散.最终在探测器端可以得到目标回波信号脉冲压缩后的结果.该方案无需脉冲压缩过程中数字化和离线处理,且具有脉冲压缩比的调谐作用.理论、数值仿真和实验证明了该设计方案能有效进行线性调频信号的光域脉冲压缩.实验产生了C波段下时宽1.2ns,带宽3.2GHz的线性调频信号,并通过互逆色散光纤将该信号压缩到了0.09ns,脉冲压缩比达13.3.     

Possibility of X‐ray pulse compression using an asymmetric or inclined double‐crystal monochromator

It is shown theoretically that the asymmetric or inclined double‐crystal X‐ray monochromator may be used for X‐ray pulse compression if the pulse is properly chirped. By adjusting the mutual distance of the two asymmetric or inclined crystals it should be possible to achieve even a sub‐femtosecond compression of a chirped free‐electron laser pulse. The small d‐spacing of the crystal enables a more compact scheme compared with the currently used grating compression scheme. The asymmetric cut of the crystal enables the acceptance of a larger bandwidth. The inclined cut has larger tunability.     

Stimulated Brillouin scattering phase conjugation of light beams carrying orbit angular momentum(Invited Paper)

We investigate the stimulated Brillouin scattering(SBS)properties of light beams carrying orbit angular momentum(OAM).The phase conjugation of light beams carrying OAM is experimentally achieved in an SBS mirror with a random phase plate.The spectrum and the pulse width compression of SBS light are measured.It is shown that the phenomena of pulse compression is observed and OAM conservation is confirmed in the SBS process.The OAM transfer from photons to phonons may find potential applications in photon-phonon conversion-based signal-processing schemes by using OAM multiplexing.     

Intracavity self-phase modulation and pulse compression in mode-locked lasers

We show that in the presence of a bandwidth-limiting component intracavity selfphase modulation in high power mode-locked and Q-switched lasers is accompanied by interesting pulse-shaping phenomena. If the phase modulation is properly controlled the pulse duration can approach the limit given by the frequency bandwidth of the laser. For example, for a Nd: YAG laser our calculations predict an intracavity pulse compression by approximately a factor of ten over the typical pulse duration of conventional mode-locking.     

A new concept of white light generation using a nano-waveguide for the solar radiation collection use

We propose a novel system of a nano-waveguide that can be used to generate the continuous optical spectrum, i.e. white light. A system consists of two micro-ring resonators and a nano-ring resonator that can be integrated into a single system. The large bandwidth signal is generated using a soliton pulse propagating within a Kerr-type nonlinear medium, whereas the continuous bandwidth or wavelength of light signal can be performed. Results obtained have shown the potential of using such a system for white light source generation and amplification, which is discussed. The amplified pulse can be stored within a nano-waveguide, which is allowed to form the continuous spectrum after amplification. Alternatively, the low-level solar radiation can be amplified, and the bandwidth signals can also be enlarged.     

Spatial optimization of filaments

We demonstrate the spatial homogenization of intense laser pulses by adaptive minimization of spatial chirp of the spectrally broadened output pulses of a filament. A liquid-crystal-based two-dimensional spatial light modulator is used to control the spatial phase of the driver pulse. An evolutionary algorithm finds the optimal spatial laser phase distribution that introduces minimal distortions during filamentation and enhances the beam quality of the output pulse. A homogeneous intensity distribution favours efficient temporal compression close to the bandwidth limit without the need for spatial filtering after the filament. PACS 42.65.-k; 42.65.Re; 41.85.Ct     

双通放大受激布里渊散射脉冲压缩

文章报道了利用双通放大结构进行受激布里渊散射（ＳＢＳ）脉冲压缩，实验获得了近极限压缩的脉冲，压缩率近１０倍。实验中同时观察到脉冲压缩中的相位跃变。相位跃变是受激背散射光与入射激光间的增益与损耗调制的结果。     

Adaptive pulse compression by two-photon absorption in semiconductors

We investigate the adaptive optimization of broadband laser pulses, using a closed-loop learning algorithm in which the merit function is derived from two-photon absorption in semiconductors. Photoluminescence experiments with CdS thin films and photocurrent measurements of a GaAsP photodiode have been performed. The experimental data demonstrate that reliable and accurate pulse compression to the bandwidth limit can be achieved, unperturbed by nontrivial phase effects. Therefore two-photon absorption proves to be an easy-to-implement alternative to second-harmonic generation for the compression of broadband laser pulses.     

A novel system of the simultaneous trapping of dark-bright solitons within a nano-waveguide system

We propose a novel system of a nano-waveguide that can be used to generate the continuous spectrum, i.e. white light. The simultaneous trapping and generation of short and millimeter waves can also be performed by using either bright or dark soliton. A system consists of two micro- and a nano-ring resonators that can be integrated into a single system. The large bandwidth is generated by a soliton pulse within a Kerr-type nonlinear medium where the continuous bandwidth or wavelength can be performed. The simultaneous dark-bright solitons conversion is performed and achieved. Results obtained have shown the potential of using the technique for continuing light spectra generation, where the filtering signals are allowed by using the suitable device parameters. The advantage is that the large bandwidth separation of the short and sub-millimeter waves can be obtained, which is allowed to form the simultaneous generation of short and millimeter waves within a single system. Further, light pulse can be trapped within a nano-waveguide, which is available to form the memory device.     

超低压选择区域生长法制备产生10GHz重复率超短光脉冲的级联电吸收调制器与分布反馈激光器单片集成光源

采用超低压(22×１０^２Pa)选择区域生长(selective area growth, SAG)金属有机化学气相沉积(metal-organic chemical vapor deposition, MOCVD)技术成功制备了InGaAsP/InGaAsP 级联电吸收调制器(electroabsorption modulator, EAM)与分布反馈激光器(distributed feedback laser, DFB)单片集成光源的新型光电器件.实验结果表明，采用该技术制备的器件 关键词： 超低压 选择区域生长 集成光电子器件 超短光脉冲     

Nonlinear compression of picosecond chirped pulse from thin-disk amplifier system through a gas-filled hollow-core fiber

We theoretically study the nonlinear compression of a 20-m J, 1030-nm picosecond chirped pulse from the thin-disk amplifier in a krypton gas-filled hollow-core fiber. The chirp from the thin-disk amplifier system has little influence on the initial pulse, however, it shows an effect on the nonlinear compression in hollow-core fiber. We use a large diameter hollow waveguide to restrict undesirable nonlinear effects such as ionization; on the other hand, we employ suitable gas pressure and fiber length to promise enough spectral broadening; with 600-μm, 6-bar(1 bar = 105Pa), 1.8-m hollow fiber,we obtain 31.5-fs pulse. Moreover, we calculate and discuss the optimal fiber lengths and gas pressures with different initial durations induced by different grating compression angles for reaching a given bandwidth. These results are meaningful for a compression scheme from picoseconds to femtoseconds.     

介质参数对受激布里渊散射脉宽压缩的影响

 利用KrF激光和SF₆介质从理论和实验上研究了声子寿命和增益系数等介质参数对SBS脉宽压缩比和能量反射率的影响。理论上采用一维瞬态模型对SBS过程进行数值模拟，考虑了瞬态过程、介质吸收以及泵浦耗空的影响，计算了SBS介质不同参数对脉冲压缩影响的规律。实验表明，在实验参数的变化范围内声子寿命越短、增益系数越小，越有利于脉宽压缩。在0.68MPa下，脉宽压缩比达到8。数值模拟了声子寿命和介质增益系数单独变化时对SBS过程影响的规律，发现在声子寿命和增益系数同时变化时，SBS对泵浦脉冲的压缩有最佳点。     

Development of a Two-Dimensional Bar-Code Detection System Using Multi Laser Diodes with Time-Sharing Light Emission Operation

A new high-speed two-dimensional bar-code detection system using multi laser diodes with time-sharing light emission operation has been developed. A bias current allowing the laser diode to improve the light output rise time was optimized to slightly below the threshold of the diode, so that channel cross-talk among three-line bar-code signals caused by the bias light can be kept small and a high-speed pulse modulation operation can be achieved. The prototype system for a three-line bar code with spatially overlapping laser-diode heads has achieved an effective scanning speed two and nine tenths times that of conventional scanners. It is estimated that the number of time-sharing light emission laser diodes can be increased to at least four when the current photodetection amplifier with a bandwidth of 6.4 MHz is used. This number can be improved to six by using photodetection amplifiers with double the bandwidth of the present ones.     

Author index to volume 54

It has been experimentally shown that when light pulses propagate in active neodymium glass fibers, a decrease of amplified pulse length almost by a factor of two is observed at a fiber length of 1 m. The study of the amplification process of an ultrashort laser pulse train by a glass fiber quantum amplifier showed that the main reason of the nanosecond light pulse compression is a recombination of the short-lifetime colouring centers due to the absorption of the front of the light pulse. Experimental results are presented concerning light pulse compression at various excitation levels of active glass fibers.     

耦合环形腔马赫-曾德尔干涉仪瞬态响应及应用

对耦合环形腔马赫-曾德尔干涉仪光脉冲瞬态响应进行了理论和数值研究.利用光束追迹法推导了脉冲传输的解析关系,并数值模拟了传输光场随时间的演化.输出脉冲形状可通过控制损耗进行调解,响应速度为皮秒量级.由于马赫-曾德尔干涉仪两输出端口的互补性,在输出端可同时实现光脉冲微分和积分操作.利用损耗控制机制,可实现单通道脉冲微分和积分操作转换.引入增益补偿损耗,可实现脉冲压缩及产生可调单一触发光脉冲.