滤波对8字腔掺铒光纤激光器锁模运转的影响

构建了基于损耗非对称非线性光学环镜的8字腔掺铒光纤锁模激光器,并讨论了腔内滤波带宽对腔内脉冲演化和激光器输出特性的影响.在非线性光学环镜中引入双向输出耦合器,耦合器和传输光纤位置的不对称产生非互易性,实现锁模运转.利用自制的可调谐滤波器实验研究了滤波带宽对激光器的影响.当滤波带宽为2.1 nm时,腔内脉冲的演化过程受滤波和孤子效应的共同作用,激光器顺时针和逆时针输出脉冲半高全宽分别为583.7fs和2.94 ps.随着滤波带宽增大,滤波的作用逐渐减弱,激光器两路输出脉冲参数逐渐接近,并接近傅里叶变换极限脉冲.当滤波带宽较大时,腔内脉冲的演化过程受增益谱和孤子效应的共同作用,激光器顺时针和逆时针输出脉冲均为变换极限脉冲,半高全宽约为440 fs.通过调节滤波器中心波长实现了对激光器输出脉冲光谱的连续调谐,调节范围大于30 nm.     

Adaptive time-domain filtering for real-time spectral discrimination in a Michelson interferometer

We present a method of spectral discrimination that employs time-domain processing instead of the typical frequency-domain analysis and implement the method in a Michelson interferometer with a nonlinear mirror scan. The technique yields one analog output value per scan instead of a complete interferogram by directly filtering a measured scan with a reference function in the time domain. Such a procedure drastically reduces data-processing requirements downstream. Additionally, using prerecorded interferograms as references eliminates the need to compensate for scan nonlinearities, which broadens the field of usable components for implementation in miniaturized sensing systems. With our efficient use of known spectral signatures, we demonstrate real-time discrimination of 633- and 663-nm laser sources with a mirror scan length of 1 microm , compared with the Rayleigh criterion of 7 microm.     

激光混沌通信中半导体激光器接收机对高频信号的滤波特性

数值研究了基于半导体激光器的混沌通信系统中构成混沌同步的接收半导体激光器对高频信号的滤波特性.分析了闭环结构的接收机对不同频率、不同幅度的加载信号的提取能力.研究发现，混沌保密通信系统对传输信号的提取能力与信号的频率有关.当信号频率较低时，闭环结构的接收机对信号的滤波效果较好；当信号频率接近半导体激光器的弛豫振荡频率时，接收机的滤波效果较差.分析结果同时表明，混沌保密通信系统中接收机对传输信号的提取质量不仅与实现混沌同步的两激光器的同步质量有关，而且依赖于传输信号的幅度. 关键词： 混沌 混沌同步 半导体激光器 滤波     

Rabi frequency as a carrier frequency of radiation

An analytical formula with three-center terms has been proposed for the calculation of the dynamic spin susceptibility of electron-doped cuprates. The results of the calculation of the imaginary part of the susceptibility reproduce the main features of inelastic neutron scattering and resonant inelastic X-ray scattering. It has been shown that the high-frequency behavior of the dispersion of collective spin excitations is mainly determined by the parameters of the conduction band and hardly depends on the exchange coupling of copper spins. The spin and superconducting gap parameters, as well as correlation effects associated with the three-center terms, play the determining role in the formation of the spin response in the region Q ≈ (π, π).     

光谱滤波技术对星等测量精度的影响

白天对空间目标进行观测时,采用光谱滤波技术可以提高光电系统的极限星等探测能力。针对光谱滤波探测特点,基于现有测量方法,结合光谱反射特性,分析了光谱滤波技术对测量精度的影响,给出了修正方法;利用光电系统对某空间目标进行了实际测量,根据事后修正方法进行了仿真研究,对实际测量值与事后修正值进行了比对分析。分析表明：光谱滤波技术虽然提高了光电系统的探测能力,但对测量精度带来了较大的影响,最大精度可为0.5等星。     

光谱滤波技术对星等测量精度的影响

 白天对空间目标进行观测时,采用光谱滤波技术可以提高光电系统的极限星等探测能力。针对光谱滤波探测特点,基于现有测量方法,结合光谱反射特性,分析了光谱滤波技术对测量精度的影响,给出了修正方法;利用光电系统对某空间目标进行了实际测量,根据事后修正方法进行了仿真研究,对实际测量值与事后修正值进行了比对分析。分析表明：光谱滤波技术虽然提高了光电系统的探测能力,但对测量精度带来了较大的影响,最大精度可为0.5等星。     

Stochastic global optimization as a filtering problem

We present a reformulation of stochastic global optimization as a filtering problem. The motivation behind this reformulation comes from the fact that for many optimization problems we cannot evaluate exactly the objective function to be optimized. Similarly, we may not be able to evaluate exactly the functions involved in iterative optimization algorithms. For example, we may only have access to noisy measurements of the functions or statistical estimates provided through Monte Carlo sampling. This makes iterative optimization algorithms behave like stochastic maps. Naive global optimization amounts to evolving a collection of realizations of this stochastic map and picking the realization with the best properties. This motivates the use of filtering techniques to allow focusing on realizations that are more promising than others. In particular, we present a filtering reformulation of global optimization in terms of a special case of sequential importance sampling methods called particle filters. The increasing popularity of particle filters is based on the simplicity of their implementation and their flexibility. We utilize the flexibility of particle filters to construct a stochastic global optimization algorithm which can converge to the optimal solution appreciably faster than naive global optimization. Several examples of parametric exponential density estimation are provided to demonstrate the efficiency of the approach.     

Open and covered singing as studied by means of fiberoptics, inverse filtering, and spectral analysis

Covering the voice near the passaggio is a technique mainly used in male classic Western singing. The purpose is said to be to smooth the register transition and avoid register breaks. The physiological and acoustical differences between open and covered singing near the so-called passaggio were investigated by means of fiberoptics, inverse filtering, and spectral analysis. The study corroborated previous findings that covering physiologically means a widening and lengthening of the pharynx. Acoustically, covering implies a change of formant frequencies, and an elevated sound pressure level of the lowest source spectrum partial, i.e., the fundamental, resulting from an increased transglottal air flow. The findings indicate that covered singing also is associated with larynx lowering. Covered singing near the passaggio shows similarities to so-called phonation, and is probably preferable from the point of view of vocal hygiene.     

Negative refraction and the spectral filtering of terahertz radiation by a photonic crystal prism

We demonstrate how micromachined photonic crystals can be used to negatively refract terahertz frequency light. The photonic crystals, which are constructed from conventional dielectric materials, manipulate the incident beam via interaction with their photonic bands. Consequently, we show that different components of a broadband beam incident on the structure may be positively or negatively refracted, depending upon its frequency and that the structure can be used as an effective spectral filter of THz radiation.     

Calibration curves in atomic emission spectral analysis of biological specimens

An efficient algorithm and special software are described for plotting calibration curves in the form of polynomials of optimal degree for atomic emission spectral analysis. The operation of the software is demonstrated using software/hardware systems for monitoring the content of toxic elements in biological specimens. It is shown that using optimal calibration curves leads to a decrease in the error of the spectral analysis. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 250–253, March–April, 2006.