Spectral modulation of higher harmonic spontaneous emission from an optical klystron

Higher harmonics of spontaneous emission from an optical klystron have been observed. The modulation factor of the spontaneous emission spectrum for the higher harmonics can be described by considering the observation system. When the dispersive gap of the optical klystron was fixed, the microstructure interval of the spontaneous emission spectrum at a certain resonant wavelength became narrower as the order of the higher harmonic became larger. Some unique characteristics of the higher harmonics have been clarified, and these studies are likely to contribute to the development of free‐electron lasers using higher harmonics of an optical klystron in the shorter‐wavelengths region.     

Compton-Polarimeter für 2 MeV-Bremsstrahlung

A polarimeter for bremsstrahlung must simultaneously perform two functions: it must select photons within a small energy interval out of the continuous bremsstrahlung spectrum and it must measure the polarization of these photons. The polarimeter depends on the polarization sensitivity of the Compton process with a 5 mm Si(Li-drift) detector as scatterer and a plastic scintillator as photon detector. To improve the energy resolution of the polarimeter a second 0,5 mm Si(Li-drift) detector behind the scatterer has been placed in anticoincidence with the scatterer.     

Spectral Polarimeters Based on Integrated Acousto-Optical Ti:LiNbO3 TE-TM Converters

An integrated Ti:LiNbO3 acousto-optical TE-TM converter followed by a polarizer was used to realize a wavelength-selective polarimeter. The stop-band attenuation was shown to increase to > 28 dB when more mode converters were integrated on a chip. Based on this experience, a four-stage demonstration unit was built, and polarimetric spectra as well as the time evolution of the state of polarization were measured. Finally, a simple optical spectrum analyzer is proposed.     

Spectral Polarimeters Based on Integrated Acousto-Optical Ti:LiNbO3 TE-TM Converters

An integrated Ti:LiNbO3 acousto-optical TE-TM converter followed by a polarizer was used to realize a wavelength-selective polarimeter. The stop-band attenuation was shown to increase to > 28 dB when more mode converters were integrated on a chip. Based on this experience, a four-stage demonstration unit was built, and polarimetric spectra as well as the time evolution of the state of polarization were measured. Finally, a simple optical spectrum analyzer is proposed.     

Clover探测器的极化测量

介绍了利用Colver探测器测量γ射线的线性极化方法. 用⁶⁰Co源对其进行测试, 有效地测量了γ射线的电磁属性, 从而确定了能级的宇称.     

Parity of the band head at 3710 keV in 99Rh using clover detector as compton polarimeter

Clover detector has been used as a Compton polarimeter to measure the linear polarization of γ-rays produced in heavy ion fusion reaction. The polarization sensitivity of the clover detector has been measured over γ-ray energies ranging from 386 to 1368 ke V. The E1 multipolarity of the 1117 keV transition in ⁹⁹Rh has been established using this polarimeter. This has resulted in the assignment of negative parity to the band head at 3710 keV in ⁹⁹Rh.     

激光驻波中运动电子的谐波自发辐射

 采用单电子模型分析了电子在线极化激光驻波中的动力学及谐波自发辐射谱,数值计算了电子在驻波中的运动情况及辐射谱。结果表明:电子在波节和波腹处入射后,其辐射谱出现不同的特征;电子在波节处垂直磁场入射后,在洛伦兹力作用下快速振动并向前运动,其向后辐射的光谱发生红移,向前辐射的光谱发生蓝移,谱线出现展宽;当激光强度或者电子初始能量增大时,这些效应更加突出,以至于产生更高阶谐波,形成连续谱;而电子在波腹处以平行电场的方向入射后,仅在电场作用下作直线运动,其自发辐射谱线没有发生移动和展宽。     

中华和钟之双音鎛钟的声频特征和振动方式研究

本文对中华和种之中央Bo钟的声频特性和振动方式进行了研究。利用谱对其辐射声信号进行了谱分析;利用时频分析,研究了其谱结构随时间变化情况;为了了解其频率变化及音高情况,计算了其不同时刻的瞬时平均频率。同时,通过不同位置的振动信号谱分析,重建了其在不同频率下的振动方式。     

Observation of E.M. radiation at ƒpe and its harmonics emitted by a turbulent plasma

Electromagnetic radiation emitted by a turbulent plasma is measured. The frequency spectrum shows maxima at harmonics of the plasma frequency.     

I/f noise in systems showing stochastic resonance

Stochastic resonator systems with input and/or output 1/f noise have been studied. Disordered magnets/dielectrics serve as examples for the case of output 1/f noise with white noise (thermal excitation) at the input of the resonators. Due to the fluctuation-dissipation theorem, the output noise is related to the out-of-phase component of the periodic peak of the output spectrum. Spin glasses and ferromagnets serve as interesting examples of coupled stochastic resonators. A proper coupling can lead to an extremely large signal-to-noise ratio. As a model system, a l/f-noise-driven Schmitt trigger has been investigated experimentally to study stochastic resonance with input 1/f noise. Under proper conditions, we have found several new nonlinearity effects, such as peaks at even harmonics, holes at even harmonics, and 1/f noise also in the output spectrum.     

An Intermediate-Energy Experimental Test of Bell's Inequalty with Recoil Polarimeters

To date there has been only one test for local reality which used fermions. Lamehi-Rachti and Mittig measured correlated protons with a recoil polarimeter at Saclay. We discuss this experiment and survey the published criticism. We then propose an experiment involving a 500 MeV electron beam on a ³He target. The two protons in the ³He nucleus originally have their spins anti-aligned. The spins of the ejected protons can be measured with a recoil polarimeter and the correlation function obtained, which will be a good test of Local Reality and Bell's inequality.     

Recoil polarimetry with the Crystal Ball at MAMI

The spectrum and properties of the excited states of the nucleon are still poorly established despite decades of study. These proceedings describe new measurements of pseudo-scalar meson photoproduction at the Crystal Ball at MAMI, employing a new large acceptance nucleon recoil polarimeter. The double- and single-polarisation observables obtained will provide valuable and unique data to be used as part of the world effort to improve our knowledge of this fundamental spectrum.     

Spectroscopic polarimetry with a channeled spectrum

We describe a novel method for the spectroscopic measurement of the state of polarization (SOP) of light. A pair of thick birefringent retarders is incorporated into the spectroscopic polarimeter, so the generated channeled spectrum is composed of three quasi-cosinusoidal components carrying the information about the SOP of the light that is being measured. Fourier inversion of the channeled spectrum provides significant parameters for determination of the spectrally resolved Stokes parameters of light. No mechanically movable components for polarization control or active devices for polarization modulation are used, and all the Stokes parameters can be determined at once from only the single spectrum. The effectiveness of this method is demonstrated by the generation of elliptically polarized light whose SOP varies with wave number.     

多角度偏振辐射计系统设计与实现

多角度和偏振遥感可解决传统遥感所不能解决的大气探测和目标识别等方面的问题。为实现气溶胶偏振信息的多角度探测,提出了一种新型的多角度偏振辐射计。该辐射计可以在多个角度上测量大气的偏振光谱信息,为大气光学和微物理特性的高精度反演提供重要的实测数据源。作为航天载荷的原理样机,多角度偏振辐射计的光机系统由多路并行望远光学模块组成,可在110°视场范围内,以0.5°间隔实现偏振信息的多角度探测;采集控制与数据传输系统由双控制核心和高速接口组成,大大提高了系统的并行处理能力和数据传输速度,可在高速运动的平台上实现多路偏振光谱信息的同步采集与实时传输,避免了由平台移动和信号的异步采集引入的误差。航飞试验结果表明,多角度偏振辐射计可实现气溶胶偏振信息的高精度探测。     

Acoustic centering of sources measured by surrounding spherical microphone arrays

The radiation patterns of acoustic sources have great significance in a wide range of applications, such as measuring the directivity of loudspeakers and investigating the radiation of musical instruments for auralization. Recently, surrounding spherical microphone arrays have been studied for sound field analysis, facilitating measurement of the pressure around a sphere and the computation of the spherical harmonics spectrum of the sound source. However, the sound radiation pattern may be affected by the location of the source inside the microphone array, which is an undesirable property when aiming to characterize source radiation in a unique manner. This paper presents a theoretical analysis of the spherical harmonics spectrum of spatially translated sources and defines four measures for the misalignment of the acoustic center of a radiating source. Optimization is used to promote optimal alignment based on the proposed measures and the errors caused by numerical and array-order limitations are investigated. This methodology is examined using both simulated and experimental data in order to investigate the performance and limitations of the different alignment methods.     

Influence of an ambipolar field and target boundary blurring on transition radiation from fast electrons of laser plasma

It is shown that the blurring of the rear side of a thin laser target leads to a decrease in the intensity of higher harmonics in the spectrum of coherent transition radiation and that the scale of the boundary inhomogeneity can be estimated from the amplitude ratio of harmonics. Deceleration of the electron flow in an ambipolar electric field at the rear boundary of a target leads to a decrease in the intensity of lower harmonics in the spectrum of coherent transition radiation, and the strength of the ambipolar field can be estimated from the amplitude ratio of harmonics. A change in the permittivity of a dielectric laser target with frequency can lead to an increase in the intensity of some harmonics in the spectrum due to the Vavilov-Cherenkov mechanism.     

铯原子蒸气薄池中的透射光谱

对单光束通过蒸气薄池中的铯原子6S1/2→6P3/2跃迁的透射光谱进行了实验研究，其透射光谱呈现出亚多谱勒特性。利用频率调制技术提高信号的灵敏度，同时研究了激光强度对信号的影响。     

Using of Digital Demodulation of Multiharmonic Overmodulated EPR Signals to Improve EPR Oximetry Reliability

Overmodulation of electron paramagnetic resonance (EPR) lines is routinely used in EPR oximetry in order to increase the signal-to-noise ratio and thus to improve the accuracy with which the line width of a spin probe can be measured. For a known probe type, the line width is easily translated into the oxygen partial pressure. A standard EPR spectrometer uses the analog phase-sensitive detection (PSD) to demodulate the EPR signal. PSD imposes the restriction that only one spectrum is measured at a time, which is normally the first-harmonic EPR line. Information about EPR signals centered at the other harmonics of the modulation frequency is irreversibly destroyed by PSD. The question is raised whether this information can be utilized for EPR oximetry, for overmodulation enhances the second- and the other harmonic spectra, so that they approach the first-harmonic spectrum in intensity. To find an answer, numerical simulation and experimental measurements have been conducted. The experiment required modification of the detection scheme, so that all EPR-related information in the overmodulated signal is preserved. This permits measuring of the multiharmonic EPR spectrum, which when fitted to a set of the corresponding theoretical lines produces more accurate results in comparison with the standard overmodulation method.     

Differential polarization of photoneutrons from deuterium

The differential polarization of photoneutrons from deuterium has been measured at lab reaction angles of 45° and 90° for incident unpolarized photons in the energy range 7 to 30 MeV. The polarization is measured by observing the left-right asymmetry in the elastic scattering of neutrons from a liquid-helium polarimeter which is used in conjunction with a nanosecond time-of-flight spectrometer. At the lowest energies, the ¹²C(n, n)¹²C reaction is used as an analyser. The left-right asymmetry is determined by using the spin-precession method, recently developed for use with a continuous energy spectrum of neutrons. Two independent difference experiments are carried out using C²H₂-CH₂ and H₂O-H₂O targets in order to detect possible target-dependent systematic errors. Departures from the predictions of current theories of the photo-disintegration of the deuteron are observed at both reaction angles.     

Absolute polarimeter for the proton-beam energy of 200 MeV

A polarimeter is upgraded and tested in a 200-MeV polarized-proton beam at the accelerator-collider facility of the Brookhaven National Laboratory. The polarimeter is based on the elastic polarizedproton scattering on a carbon target at an angle of 16.2°, in which case the analyzing power is close to unity and was measured to a very high degree of precision. It is shown that, in the energy range of 190–205 MeV, the absolute polarization can be measured to a precision better than ±0.5%.