光纤中基于交叉相位调制与喇曼放大的超短光脉冲串的产生

本文提出一种在单模光纤负群速色散区连续波产生超短光脉冲串的新方法，即让波长位于光纤负色散区的连续波和波长位于光纤正色散工铁泵浦脉冲串在光纤中共同传输，在光纤的零色散波位于连续波长与泵浦脉冲波长中间附近的情况下，交叉相位调制与喇曼放大能使连续波演化成比泵浦脉冲窄得多的无调啾，无脉座的超短光脉冲串。数值计算表明，泵浦脉冲愈强，由连续波产生的超短光脉冲宽度愈宽，峰值功率愈高，而且所需的光纤愈短。     

转镜式快速扫描自相关器的研究

本文描述一种用于飞秒激光脉冲宽度测量的自相关装置。它可令光脉冲产生周期性的时间延迟。借助于示波器,可以显示出激光脉冲强度的二次相关曲线,从而实现对周期性飞秒脉冲宽度的实时快速监测。     

Investigation of the characterstics of a mode-locked Nd:Glass laser with the aid of a picosecond streak camera

An infrared-sensitive streak camera, capable of resolving optical pulses of durations of ∼3 ps, has been used to analyze the temporal development of the individual picosecond pulses in a mode-locked pulse train. A progressive increase in the duration of the individual pulses throughout the pulse train is observed, the rate of increase in the pulse duration being an approximate quadratic function of the optical field. In addition, temporal analysis of the laser output signal, dispersively delayed with the aid of a grating pair, confirms the existence of phase-modulation effects during the development of the mode-locked pulse train.     

A posteriori joint detection and discrimination of pulses in a quasiperiodic pulse train

The problem of a posteriori joint detecting and discriminating pulses in a quasiperiodic pulse train is studied. By the quasiperiodic pulse train, we mean any pulse train in which the time lapse between the beginning instants of two consecutive pulses varies over time within a certain fixed interval. We consider the kind of quasiperiodic pulse train in which the beginning instants of pulses are deterministic (nonrandom). We analyze the case when all pulses in a pulse train belong to an alphabet of reference pulses having identical duration. It is assumed that the observed interval of the pulse train contains the complete pulses (no parts of pulses are missing at the observation) and that the unobservable pulse train is distorted by an additive white Gaussian noise. Up until this time, there has been no exact algorithm to solve this a posteriori problem under these very simple assumptions because of enormous combinatorial complexity. We derive and prove an efficient (polynomial) computing algorithm for the exact solution to this problem. The recursive equations for step-by step discrete optimization are obtained under the maximum-likelihood criterion. The same formulas hold under the least-squares criterion. The computational load of the algorithm is evaluated, and its dependency on the parameters of the problem is proven.     

Power spectrum of a pulse train specified by its probability-generating function

A stationary stochastic train of nonoverlapping pulses is considered, and a link is established between the conditional probability density pk(?) for the appearance of k successive count-to-count intervals during the time interval ?, assuming that the first count-to-count interval has begun (with the first pulse) at t = 0, and that the kth interval has ended (with the last pulse) at t = ?, and the probability Gj(?) that j successive pulses of this train will appear during the same time interval ? (supposing that the initial time t = 0 has been selected at random). If the train considered consists of identical unit pulses, it is also possible to relate to Gj(?) its autocorrelation function R(?), as well as its power density P(?).     

Antisymmetric pulse generation using phase-shifted fibre Bragggrating

A 10 mm Bragg grating with a 0.18 nm (peak-to-peak) spectral response was designed to shape a train of 7 ps Gaussian pulses into antisymmetric Hermite-Gauss pulses. The pulses were characterised in the frequency and time domain. The presence of the phase shift was verified by propagation in standard fibre     

利用脉冲复制环提高纳秒脉冲单次测量的动态范围

提出了一种提高纳秒光脉冲单次测量动态范围的方法,其中光纤脉冲复制环用来产生时域上幅度呈指数递减的脉冲复制串,有效环增益为0.955。经软件补偿脉冲复制串使其具有相同的幅度,然后累加平均前18个脉冲,能够将注入的单发纳秒光脉冲动态范围提高2.74倍,这样就可以实现利用光电探测管和示波器对100:1高对比度的惯性约束核聚变(ICF)脉冲测量。     

Electrostrictive self-focusing of picosecond laser pulse trains

A nanosecond-long train of picosecond laser pulses theoretically can produce self-focusing by electrostriction, even though the trapping threshold for a single picosecond pulse is very high. The relative roles of electrostriction and various types of Kerr effect in picosecond pulse train self-focusing should be assessed.     

Dynamic analysis of mode-locked sampled-grating distributed Braggreflector laser diodes

A mode-locked sampled-grating distributed-Bragg-reflector (SGDBR) laser diode for generating a train of light pulses at terahertz repetition rates is proposed with a numerical analysis based on a time-domain large-signal model. The device consists of three parts: the saturable absorber section which serves as a mode-locker, the gain section as an amplifier, and the SGDBR as a spectrum filter. It is predicted that spectrum filtering of the SGDBR along with passive mode locking due to the saturable absorber is effective in generating a train of transform-limited mode-locked pulses at a high repetition rate     

Theory and simulation of the dynamics and stability of actively modelocked lasers

A new model is proposed for the active modulation component of a mode-locked laser cavity. By using Jacobi elliptic functions to capture the periodic forcing to the cavity, we are able to construct exact solutions representing a mode-locked pulse train. Two families of pulse-train solutions are generated: one in which neighboring pulses are in-phase and a second in which neighboring pulses are out-of-phase. We show that only out-of-phase solutions allow for stable mode-locked pulse trains. Further, pulse-to-pulse interactions can generate instabilities that destroy the pulse train altogether or lead to Q-switching.     

Repetition-frequency multiplication of mode-locked pulses usingfiber dispersion

In this paper, we describe a novel method for generating a highly repetitive optical pulse train using mode-locked pulses and the group-velocity dispersion (GVD) of optical fiber. An optical pulse train at a multiplied repetition frequency oscillation of an initial mode-locked pulse train is obtained by adjusting waveform fiber length in accordance with the mode-locking frequency and the fiber's GVD. A subterahertz optical pulse train (98-196 GHz) was successfully generated with low pulse intensity fluctuation     

单个微微秒脉冲的研究

由被动锁模钕玻璃激光器产生的锁模脉冲序列中,分别从不同位置选出单脉冲,并研究了它们的时间和光谱特性。实验表明,在时间和光谱分布上满足高斯型的带宽极限脉冲,是呈现在序列的前部。随着序列的延续,光谱宽度显著加宽,并有明显的调制现象。加宽与理论计算符合很好,证明了加宽主要是强光下的自相位调制所引起。最后,对实验中的某些现象进行了讨论。     

从锁模脉冲序列中先后选出两个单脉冲的同步研究

采用再生放大腔内的短程放大,利用硅光导开关的长的复合时间,实现光导后产生快上升和下降时间、宽度可调的千伏电脉冲,完成从锁模脉冲序列中先后选出两个单脉冲,这两个单脉冲同步精度高、运转稳定。     

A plasma shutter for far-infrared laser radiation

A new type of a plasma shutter for far-infrared (FIR) laser radiation is presented. This plasma shutter blocks a FIR laser beam within 0.7 ns by a rapidly expanding plasma. This device has been applied to produce FIR pulses with variable duration between 10 and 100 ns and to select 1-ns FIR pulses from a pulse train     

Detection performance of the narrow-band Wilcoxon detector against Gaussian noise (Corresp.)

Two adaptations of the nonparametric Wilcoxon test for use in detecting a coherent train of narrow-band signal pulses with unknown starting phase in a background of statistically undefined noise have been proposed in the literature. The performance of these detectors when the noise is stationary Gaussian is determined and compared. For a finite train of signal pulses, results were obtained by Monte Carlo simulation using the variance-reducing technique of importance sampling. For the best of the two narrow-band Wilcoxon detectors a comparison with the optimum parametric detector shows that for a train of 30 signal pulses and a false-alarm probability ofP_f = 10^{-6}the loss is about 2 dB, while for 50 signal pulses the loss is reduced to 1 dB. The theoretical asymptotic loss is 0.2 dB.     

Generation of super-stable 40 GHz pulses from Fabry-Perot resonator integrated with electro-optic phase modulator

A simple technique for converting a continuous-wave laser beam into a stable pulse train with high repetition frequency is demonstrated. The generated train is based on the synthesis of its Fourier spectrum which is composed of higher-order sidebands produced by a Fabry-Perot resonator integrated with an electro-optic phase modulator. Super-stable 40 GHz, transform-limited optical pulses are successfully generated.     

Short pulse generation in a visible diode laser by resonantexcitation of a sustained oscillation

A stable 400-MHz train of 670-nm, 100-ps pulses occurs when a gain-guided InGaP-InGaAlP diode laser is modulated in synchronicity with its sustained oscillation. Experimentally, the pulse width decreases and the peak power increases as the RF power increases. At high RF powers, the average output power of the laser shows dips or resonances around those frequencies where short pulses occur     

Spectra of short, locked magnetron pulses

A theoretical explanation is given for the observed difference between the frequency at which the peak of the spectrum of a train of short, locked magnetron pulses occurs and the frequency of the CW locking signal.     

Pulse-amplitude equalization in a rational harmonic mode-locked fiber ring laser by using modulator as both mode locker and equalizer

A simple method, by letting the pulses pass through an electrooptic intensity modulator twice, for the amplitude equalization of high repetition rate pulses generated from a p-order rational harmonic mode-locked fiber ring laser when p<5 was proposed. The modulator was used as both a mode locker and a pulse-amplitude equalizer in the cavity. A theoretical explanation based on time-domain analysis was used to find appropriate parameters to obtain an equalized pulse train and the experimental results agree with the theory.     

Experimental study of stimulated Brillouin and Raman scatterings in a Q-switched cladding-pumped fiber laser

Characteristics of stimulated Brillouin and Raman scatterings (SBS and SRS) in a Q-switched cladding-pumped ytterbium (Yb)-doped fiber laser are experimentally investigated. A stable SBS pulse train with a width of ∼2 ns and a peak power of ∼1.0 kW can be generated in regular Q-switching processes under certain conditions. The time jitter and intensity fluctuation of SBS pulses are presented, and their mechanism and statistics are discussed. The accompanied Raman–Stokes waves in regular Q-switched pulses and SBS pulses are quantitatively compared.