北京同步辐射XAFS实验方法新进展

近年来基于现有的XAFS站线条件,与用户互相配合在发展实验方法,开拓XAFS的应用方面做了一些新的尝试.主要包括高温熔态XAFS实验、全反射XAFS方法、及发光XAFS实验方法.文中分别介绍了以上几种实验方法的意义,实验设置及实验结果,并进行了讨论.     

RLC串联谐振电路实验方法改进探究

针对传统实验方法存在操作繁琐、谐振点附近电压变化缓慢等问题,提出了改进实验测量的方法,通过测量电容电感两端合电压与信号源输出电压的比值随频率变化曲线来测定谐振频率。与传统实验方法对比表明,该实验方法不仅能达到与传统实验方法相同的实验结果,而且能改进实验操作,并加深学生从不同角度对电路谐振特性的理解。为RLC串联电路谐振频率的测量提供了新的思路和切实可行的实验方案。     

磁聚焦法测定电子比荷实验的改进方法探究

随着科学技术的发展,出现了多种测定电子比荷的方法,其中在近代物理实验中常用的方法是磁聚焦法.本文在此实验设备和实验方法的基础上,研究了实验测量过程中荧光屏上显示扫描的线段随所加励磁电流的变化关系,并进一步对实验提出了改进意见.     

CCD技术在塞曼效应实验中应用的改进

利用CCD图像采集和计算机图像程序处理技术改进了塞曼效应实验系统,对比了测微目镜测量干涉圆环直径、利用手动方法处理实验图像以及利用计算机程序处理实验图像3种方法的实验结果.实验结果表明:利用计算机程序自动处理实验图像的方法能够简化实验并减小实验误差.     

在分光计上做双棱镜干涉实验

提出在分光计上做双棱镜干涉实验的实验方法,并论述了该方法的实验原理,给出了测量光波波长的公式.该方法克服了在光具座上进行实验时的调节难度大、不易测量和测量误差大等问题.     

牛顿环实验最佳方法的对比

牛顿环干涉实验是大学物理实验的一个基本实验,基于学者提出的逐差法计算方法,本文比较了两种逐差方法,运用Mathematics软件进行数据处理,得到牛顿环实验的最佳测量方法、最佳计算方法和最佳处理方法.利用计算机对实验数据进行处理的方法,既培养了学生的计算机应用能力,又为实验数据处理提供了方便,简化了大量烦琐的计算.     

“声光衍射与液体中声速的测定”实验改进探析

本文在分析"声光衍射与液体中声速的测定"实验原理的基础上,提出了实验改进方法,组装了一套简单可行的测量衍射光斑中心位置的实验装置,减小了传统实验方法中测量光斑间距的误差,提高了实验精度。     

浅谈"平分"方法在物理实验中的应用

介绍了“平分”方法的数学原理,结合典型的物理实验,针对具体的实验过程,给出了该方法的一些应用实例,并讨论了在实验中应用该方法的重要性.     

义务教育阶段物理实验方法研究及其启示

为了更好地开展义务教育阶段物理实验教学,对物理实验方法进行了研究.根据物理实验过程,可将物理实验方法分为实验操作方法和数据处理方法.通过梳理《义务教育物理课程标准(2022年版)》中学生必做的物理实验,归纳其所蕴含的实验方法,并在此基础上总结各物理实验方法的内涵和意义,以期为物理实验教学及研究提供借鉴.     

光磁共振实验中抵消地磁场垂直分量的方法

介绍了光磁共振实验装置的各磁场线圈,分析了光磁共振实验中抵消地磁场垂直分量传统方法的缺陷,利用垂直磁场对磁共振信号的影响,提出了一种重复性较好的抵消地磁场垂直分量的方法,减小了传统实验方法产生的误差.这种方法也可用于测量地磁场垂直分量的大小.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.