Measurement of intense ultraviolet subpicosecond pulses usingdegenerate four-wave mixing

Background-free measurement of the third-order intensity autocorrelation function of ultraviolet subpicosecond pulses is demonstrated. The method provides the pulse duration and additional information about asymmetry and other interesting structural properties of the pulses. It is possible to obtain the complete autocorrelation function from a single pulse. Measurements of subpicosecond pulses from XeCl excimer laser amplifiers reveal a distinct satellite structure, which can be attributed to a quantum beat effect of the XeCl lasing transitions     

IBMPC/XT计算机控制精密光学自相关器和实验数据采集与处理自动化系统

本文介绍一种用于皮秒和飞秒级超短激光脉冲和激光与物质相互作用的超快过程测量的IBMPC/XT计算机控制精密光学自相关器和实验数据采集与处理自动化系统。该系统既可进行自相关测量,又可进行干涉强度自相关测量。仪器的时间分辨率达0.3fs.     

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。     

Evaluation of intensity shape and phase change of light pulses withfrequency chirp due to self-phase modulation

A method for evaluating ultrashort light pulses is proposed. The temporal shape and the time-dependent phase change of the pulses is determined using self-consistent iterative calculations based on experimental data of the second-harmonic intensity autocorrelation and the spectra of the pulses. The self-phase modulation originating from the optical Kerr effect (OKE) and/or the saturable effect in the absorber dye solution is taken into account, and two parameters, the amount and the recovery time of the OKE, are introduced into the calculation of the temporal shape and the phase change of the pulses. These two parameters are chosen to give the best agreement of experimental and calculated second-harmonic intensity autocorrelation and spectra. The calculated results determined the lower limits of the recovery time of the OKE     

短脉冲在色散平坦光纤中传输前后波形、相位和啁啾测量的实验研究

二次谐波频率分辨光学门(SHG-FROG)是能够准确测量短脉冲多项特性参量的新技术。利用二次谐波频率分辨光学门脉冲分析仪对在色散平坦光纤中传输前后的短脉冲进行了测量,得到了待测光脉冲的频率分辨光学门(FROG)图、自相关曲线、自相关频谱曲线、波形和相位曲线以及脉宽、谱宽、啁啾等反映短脉冲特性的信息,对实验结果进行了分析,并与高斯脉冲在单模光纤中的线性传输理论进行了比较。结果表明,激光器输出的短脉冲是具有负线性啁啾的近变换极限高斯脉冲,经过12.7 km色散平坦光纤传输后仍然为具有负线性啁啾的高斯脉冲,其谱宽在传输过程中基本保持不变,脉宽展宽了3.1倍,啁啾增大了4倍。实验测量结果和理论预期一致。     

一种双正弦信号的快速频率测量方法

信号频率测量在雷达信号处理中起到重要的作用。基于DFT和自相关理论,该文提出了一种双正弦信号频率的快速估计方法。该方法先用DFT估计其中一个频率及其幅度,以此频率对信号解调并对消该频率成分,最后利用自相关理论估计信号的频差。计算机模拟证实了方法具有精度高、测频速率快的特点。     

Heterodyne autocorrelation method for characterizing 1.55 μmoptical pulse train and for measuring dispersion and nonlinearity inoptical fibers

Heterodyne autocorrelation measurement of 1.55 μm optical pulses from an actively mode-locked external cavity diode laser is performed before and after transmission through an optical fiber. In heterodyne autocorrelation, optical spectrum is resolved electronically. This method is suitable for measurement of optical pulses with a spectral width of less than 100 GHz, and it gives not only the pulse width and chirp of the pulses, but also it is useful for determining the dispersion and optical Kerr constant of an optical fiber. Analytical formalism for deducing these quantities is given for Gaussian pulses. Principal measurement is performed using a mode-locked diode laser. Dispersion is measured for a conventional-dispersion fiber of 35 km. Also, self-phase modulation (SPM) is measured for a dispersion-shifted fiber of 15.83 km     

基于六波混频的双波长红外光信号研究

利用钛宝石激光脉冲在铷原子蒸汽中通过非线性光学混频产生两个不同波长的红外光脉冲信号。研究了铷原子数密度、泵浦激光强度以及光脉冲啁啾对两个红外光信号之间竞争特性的影响。结果表明,两个红外光信号主要产生于两个耦合的差频参量六波混频过程;信号的强度随铷原子数密度、泵浦激光强度和光脉冲啁啾发生变化;两个红外光信号间的竞争主要由两个参量六波混频过程的相位匹配决定,相位匹配与铷原子数密度相关度很强,而与泵浦激光强度和光脉冲啁啾相关度很弱。     

Novel Spectrally Efficient UWB Pulses Using Zinc and Frequency‐Domain Walsh Basis Functions

In this paper, two sets of spectrally efficient ultra‐wideband (UWB) pulses using zinc and frequency‐domain Walsh basis functions are proposed. These signals comply with the Federal Communications Commission (FCC) regulations for UWB indoor communications within the stipulated bandwidth of 3.1 GHz to 10.6 GHz. They also demonstrate high energy spectral efficiency by conforming more closely to the FCC mask than other UWB signals described in the literature. The performance of these pulses under various modulation techniques is discussed in this paper, and the proposed pulses are compared with Gaussian monocycles in terms of spectral efficiency, autocorrelation, crosscorrelation, and bit error rate performance.     

基于自相关观测的语音信号压缩感知

本文基于压缩感知技术,根据语音信号的特点,提出了一种基于自相关特性的截断循环自相关矩阵作为观测矩阵,并在此基础上,从实用的角度出发,提出了基于模板匹配的近似截断循环自相关矩阵作为观测矩阵,并证明其满足RIP特性。由语音信号与截断循环自相关矩阵、近似截断循环自相关矩阵和高斯随机矩阵分别构造相应的观测,采用BP算法来重构原始语音信号。实验表明,由2个模板元素线性组合而成的近似截断循环自相关矩阵重构原始语音信号的性能与截断循环自相关矩阵的重构性能相当,且优于经典高斯随机矩阵,而且在相同的重构性能下,其压缩比远大于高斯随机观测矩阵,对语音信号的压缩性能有了明显地提高。      

Control of noiselike pulse generation in erbium-doped fiber lasers

Noiselike generation in lasers can be controlled by changing the cavity in order to obtain pulses with unique properties. Intense noiselike pulses, as narrow as a few picoseconds, were obtained. These are two orders of magnitude narrower than pulses obtained in previous work. In long cavities, coherent and incoherent two-color noiselike generation were demonstrated. The wavelength difference between the generated pulses could be tuned in a wide wavelength range, which is much broader than the amplifier bandwidth. High-energy ≈16-nJ noiselike pulses with a broad-band spectrum and narrow intensity autocorrelation trace were also demonstrated     

飞秒激光脉冲二阶干涉自相关法测量及其精细结构研究

本文用二阶相干自相关法测量飞秒激光脉冲宽度，测量过程完全由计算机控制和完成，测量精度达０．３飞秒。并分析了测量曲线的精细结构，发现其精细结构主要是由基频光相干场的振动频率所决定。     

用干涉自相关包络宽度测量超短激光脉冲啁啾

为了测量超短激光脉冲啁啾值,提出了一种用2次干涉自相关包络宽度测量啁啾值的简单方法。利用2次干涉自相关包络宽度对啁啾有很高的灵敏度、含有不同啁啾量的超短激光脉冲有不同的包络宽度的特性,通过对高斯型强度分布的线性、平方及立方啁啾的干涉自相关包络函数进行了理论分析,得到包络宽度与啁啾量值之间的对应关系。采用干涉自相关2次谐波检测系统对加浓染料激光器输出的含有啁啾的脉冲进行测量,其干涉自相关包络宽度为1.15,被测超短激光脉冲啁啾为1.0。结果表明,根据含有啁啾的干涉自相关曲线两翼的特征,可判断啁啾阶数,再根据包络宽度与啁啾值的对应关系,可估定啁啾量值;用干涉自相关包络宽度能容易地测量超短激光脉冲的啁啾量值。     

New calculation methods for echo-ranging ambiguity

In correlation echo ranging the ambiguity, or square of the signal autocorrelation envelope, is important, and two new approaches are presented that speed up general ambiguity calculations. Some signals such as linear FM can be represented by lines in a frequency-time plot, and for two such lines the cross ambiguity is associated with the point of crossing and depends on the angle of crossing. This method is extended to curved lines, including lines that touch rather than cross. Other signals have a noiselike modulation, and may be conveniently described by a distribution of spectral intensity in the frequency-time plot. For two such noise signals the mean value of the cross ambiguity depends very simply on the overlap of the two distributions. In the limit the two approaches are shown to give answers consistent with one another. In one illustrative application it is shown that, with symmetrical pulse forms, a high ambiguity at the extremes of the ambiguity diagram is always accompanied by an ambiguity concentration near the origin. In another example the ambiguity diagrams and general behavior are calculated for straight and slightly curved lines (FM pulses), for both the narrowband and wideband cases.     

Time-resolved optical gating based on dispersive propagation: a newmethod to characterize optical pulses

We introduce the technique of time-resolved optical gating (TROG) based on dispersive propagation (DP), a new noninterferometric method for characterizing ultrashort optical pulses in amplitude and phase without the need for a short optical gating pulse. TROG is similar to frequency-resolved optical gating except that the role of time and frequency is interchanged. For the DP-TROG geometry, we show that measurements of the autocorrelation trace of the pulse after propagation through a medium with variable dispersion together with a single measurement of its intensity spectrum contain sufficient information to reconstruct the pulse in amplitude and phase. Pulse reconstruction for this DP-TROG geometry works very well even for the case of a nonlinearly chirped double pulse. Compared with other methods, DP-TROG does not introduce an ambiguity in the direction of time for the pulse. Due to its simplicity and improved sensitivity. DP-TROC is expected to be useful in characterizing low-energy pulses     

飞秒脉冲干涉自相关修正光谱的啁啾特性

为了测量飞秒激光脉冲啁啾,采用了一种对干涉自相关光谱作频谱修正的简单方法,得到干涉自相关修正光谱.利用该修正光谱对啁啾有很高灵敏度的特性,对高斯型强度分布的线性啁啾、平方啁啾脉冲进行了理论分析和实验验证,取得了修正光谱的下包络峰的高度与啁啾量对应关系、下包络峰的个数与啁啾次数对应关系.结果表明,根据干涉自相关修正光谱下包络的峰值,可估定啁啾的量值,根据干涉自相关修正光谱下包络峰的个数可以判断脉冲啁啾的次数.这一结果对精确地测量飞秒激光脉冲的微小啁啾量是有帮助的.     

基于延迟自相关特性的码速率测量技术

通信信号的识别与解调是通信侦察的重要研究内容,在通常情况下,通信信号的很多参数并不知道。本文介绍了一种基于通信信号码延迟自相关特性的码速率测量技术,并给出了码速率测量理论分析及基于硬件的实现技术,仿真和实验结果表明本方案具有较高的测量性能。     

Chaos-Based transmitted-reference ultra-wideband communications

Transmitted-reference (TR) ultra-wideband (UWB) communication systems have gained increasing popularity for the usage in the low data rate application, due to its non-coherent receiver structure. In conventional TR system, non-coherency at the receiver is achieved by sending reference pulses prior to the data-bearing pulses. Then, at the receiver side, reference pulses are used as template signals for correlation with data-bearing pulses. Therefore, the orthogonality between reference and data pulses is obtained in time division multiple access (TDMA) fashion. However, the implementation of a wideband delay line is very difficult in the current low power integrated circuits. In this paper, a TR method called Chaos-Based TR (CB-TR) is proposed. In the proposed method, chaotic sequences are used to separate the reference and data pulses. Such approach exploits the benefits of chaotic signals, such as non-periodicity, easy-to-generate, impulse-like autocorrelation value and low cross-correlation value. Furthermore, in order to decrease the influence of some negative properties of conventional chaotic maps, a modified chaotic generator (MCS) is proposed. Simulation results over the IEEE 802.15.4a channel model show comparable bit error rate performance to other TR methods.     

Wigner spectrograms for femtosecond pulse-shaped heterodyne andautocorrelation measurements

We develop a mixed time-frequency representation for the calculation and interpretation of coherent optical measurements. Heterodyne and autocorrelation signals are expressed in terms of a mixed material response function and a Wigner distribution for the incoming pulses, the detected field, and the gating device. Applications to pump-probe spectroscopy, spontaneous light emission, and impulsive four-wave mixing (three-pulse echoes) are discussed     

旋转中空角体棱镜式实时自相关器

提出并实验研究了采用旋转中空角体棱镜作为光学延迟器的二阶实时光学自相关器。用于飞秒锁模掺钛蓝宝石激光器输出的脉冲测试表明,该相关器运转稳定、可靠。提出了用计算机对所测相关曲线进行误差补偿的概念。