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1.
讨论了液晶相位可变延迟器(liquid crystal variable retarder, LCVR)在自旋极化电子产生方面的应用.LCVR控制入射光子的偏振度,从而实现对自旋极化电子束极化方向的调制.采用LCVR代替1/4波片和Pockels盒的优点在于其对入射光方向不敏感,传输直径大,不需要机械转动即可大波长范围的延迟,且易于校准.另外,还研制了旋转检偏器,通过示波器读出,对光子偏振性进行检测并对LCVR进行校准.
关键词:
自旋极化电子源
液晶相位可变延迟器
极化方向 相似文献
2.
Study on optical electron polarimeter and measurement of the relative Stokes parameters of weak light
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In this paper, we present the research on an optical electron polarimeter, which is used to determine the polarization of an incident electron beam by measuring the relative Stokes parameters of the fluorescence emitted from the He gas following the impact excitation with the electron beam. The fundamental theory of the optical electron polarimeter is discussed with the 33P→23S transition of He. The structure and performance of the instrument are described, which are different in some aspects from previous works. The arrangement of the experiment for measuring the relative Stokes parameters of linearly polarized weak light is also investigated, which actually involves the same processes as the polarization measurement with the incident electron beam. The results obtained are in agreement with the theoretical prediction. 相似文献
3.
Passive magnetic shielded spin polarized electron source with optical electron polarimeter
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A new GaAs(100) spin polarized electron source with an optical
polarimeter, which is employed in the field of polarized electron
and gas atom collision, is presented in detail. The apparatus is
passive-magnetic-shielded by a box and a cylinder made of
nickel--iron--molybdenum soft magnetic alloy without Helmholtz coil
arrangement. And a uniformly distributed residual magnetic field of
less than 5×10-7,T is obtained near the collision area. The
spin polarized electron beam is transmitted and focused onto
collision point from photocathode by a set of electron optics with
more than 25% transmission 95cm distance through an 1mm
diameter aperture. Construction and operation of the apparatus, such
as vacuum and magnetic shielding system, photocathode, laser optics,
electron optics and polarimeter are discussed. The polarization of
the spin polarized electron beam is determined to be 30.8\pm3.5%
measured with a He optical polarimeter. 相似文献
4.
We predict theoretically the optical signatures of spin polarization of carriers in self-assembled quantum dots. The emission spectra are mapped out as a function of increasing electron spin polarization for a fixed number of electrons and holes. The spin-polarized spectra are determined using exact diagonalization techniques for up to 12 particles, corresponding to two lowest filled shells. We predict that the spin polarization leads to photon polarization, to redshifts of emission lines due to excess exchange interactions among the spin-polarized electrons, and to a complete breakup of emission lines for spin-polarized electronic shells. 相似文献
5.
6.
We show that the addition of a polarization controller and bias differential group delay to a spectral polarimeter increases the amount of polarization information that can be extracted from a Stokes spectrum measurement. We use this biased spectral polarimetry on 40-Gbit/s signals to measure the polarization mode dispersion of the optical fiber through which they propagate. Our measurements do not require any control of the polarization at the fiber input. Averaging measurements from several settings of the polarization controller yields improved accuracy, and, after data rejection is applied, both the accuracy and the number of valid data points is increased when using several measurements. 相似文献
7.
J. Diefenbach Y. Imai J. Han Lee F. Maas S. Taylor 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):555-559
For modern parity violation experiments it is crucial to measure and monitor the electron beam polarization continuously.
In the recent years different high-luminosity concepts, for precision Compton backscattering polarimetry, have been developed,
to be used at modern CW electron beam accelerator facilities. As Compton backscattering polarimetry is free of intrinsic systematic
uncertainties, it can be a superior alternative to other polarimetry techniques such as M?ller and Mott scattering. State-of-the-art
high-luminosity Compton backscattering designs currently in use and under development at JLab and Mainz are compared to each
other. The latest results from the Mainz A4 Compton polarimeter are presented. 相似文献
8.
9.
The Qweak experiment at Jefferson Lab aims to make a 4% measurement of the parity-violating asymmetry in elastic scattering at very low Q 2 of a longitudinally polarized electron beam off a proton target. One of the dominant experimental systematic uncertainties in Qweak will result from determining the beam polarization. A new Compton polarimeter was installed in the fall of 2010 to provide a non-invasive and continuous monitoring of the electron beam polarization in Hall C at Jefferson Lab. The Compton-scattered electrons are detected in four planes of diamond micro-strip detectors. We have achieved the design goals of <1% statistical uncertainty per hour and expect to achieve <1% systematic uncertainty. 相似文献
10.
Tashenov S Bäck T Barday R Cederwall B Enders J Khaplanov A Poltoratska Y Schässburger KU Surzhykov A 《Physical review letters》2011,107(17):173201
Atomic-field bremsstrahlung has been studied with a longitudinally polarized electron beam. The correlation between the initial orientation of the electron spin and the angle of photon polarization has been measured at the photon high energy tip region. In the time reversal this corresponds to a so-far unobserved phenomenon of production of longitudinally polarized electrons by photoionization of unpolarized atoms with linearly polarized photons. The results confirm the fully relativistic calculations for radiative recombination and suggest a new method for electron beam polarimetry. 相似文献
11.
We investigated the structural and magnetic properties of Fe(1 1 0) for molecular oxygen adsorption at room temperature. For the c(2 × 2) and c(3 × 1) superstructures, spin-polarized secondary electron emission (SPSEE) induced by protons and electrons reveals a nearly unchanged polarization compared to clean Fe(1 1 0). An appreciable decrease in polarization is found for the disordered layer of oxygen at a coverage Θ ≈ 1. This decrease is more pronounced for the spin polarization determined by electron capture (EC) to excited atomic He levels after grazing scattering. From a comparison of data obtained by proton-induced SPSEE and spin-polarized EC we conclude that the polarization at the vacuum boundary vanishes for an oxygen coverage Θ ≈ 1 while the polarization in the underlying Fe substrate layers is hardly changed. 相似文献
12.
In the framework of the Landauer-Büttiker formalism, we investigate coherent spin transport through a transverse-biased magnetic zigzag-edge graphene nanoribbon, with a temperature difference applied between the source and the drain. It is shown that a critical source temperature is needed to generate a spin-polarized current due to the presence of a forbidden transport gap. The magnitude of the obtained spin polarization exceeds 90% in a wide range of source temperatures, and its polarization direction could be changed by reversing the transverse electric field. We also find that, at fixed temperature difference, the spin-polarized current undergoes a transition from increasing to decreasing as the source temperature rises, which is attributed to the competition between the excited energy of electrons and the relative temperature difference. Moreover, by modulating the transverse electric field, the source temperature and the width of the ribbon, we can control the device to work well for generating a highly spin-polarized current. 相似文献
13.
The influence of inelastic effects on electron quantum transport through the potential relief of a dimer system was studied by exact solution of the Schrodinger equation. The nature of this problem is due to the coherent superposition of the different potential profiles through which the spin-polarized electron tunnels. It was found that the low magnetic field initiates new peaks of resonant tunneling. In high magnetic fields, the transport of electrons with opposite spin polarization is qualitatively different. 相似文献
14.
A Stokes-Mueller matrix polarimetry system consisting of a polarization scanning generator (PSG) and a high-accuracy Stokes polarimeter is used to sense the glucose concentration in aqueous solutions with and without scattering effects, respectively. In the proposed system, an electro-optic (EO) modulator driven by a saw-tooth waveform voltage is used to perform full state of polarization (linear/circular) scanning, while a self-built Stokes polarimeter is used to obtain dynamic measurements of the output polarized light intensity. It is shown that the measured output Stokes vectors have an accuracy of 10−4, i.e., one order higher than that of existing commercial Stokes polarimeters. The experimental results show that the optical rotation angle varies linearly with the glucose concentration over the range of 0-0.5 g/dl. Moreover, glucose sensing is successfully achieved at concentrations as low as 0.02 g/dl with a resolution of 10−6 deg/mm and an average deviation of 10−4 deg. In general, the polarimetry system proposed in this study provides a fast and reliable method for measuring the Stokes vectors, and thus has significant potential for biological sensing applications. 相似文献
15.
J. Kirschner 《Applied Physics A: Materials Science & Processing》1987,44(1):3-11
The use of spin-polarization analysis in electron spectroscopy of magnetic and non-magnetic surfaces is demonstrated with a few examples. The existence and properties of spin-dependent transmission of electrons through the solid-vacuum interface is shown. The influence of surface reconstruction of Pt(110) on spin polarization and energy distribution curves in photoemission with circularly polarized light is studied. The polarization of secondary electrons from Fe(110) is observed to depend on the spin polarization of primary electrons at low energies. The temperature dependence of the exchange splitting in Ni is studied by means of spin-polarized electron energy loss spectroscopy and found to be at variance with the assumptions of the Stoner-Wohlfarth theory. 相似文献
16.
D. Conrath T. Heindorff A. Hermanni N. Ludwig E. Reichert 《Applied Physics A: Materials Science & Processing》1979,20(2):155-157
GaAs0.62P0.38 activated to negative electron affinity and irradiated with circularly polarized light of a wavelength shorter than approximately
680 nm emits electrons whose spins are mainly oriented antiparallel to the photon spins. At 650 nm a degree of electron spin
polarization around 40% is observed. The spectrum of spin polarization of the photoelectrons is similar to that known from
GaAs cathodes but is shifted to shorter wavelengths. 25 μA current of spin-polarized electrons were achieved with a 5 mW He-Ne
laser. 相似文献
17.
Developing accurate self-assembly is the key for constructing functional materials from a bottom-up approach.At present, it is mainly hindered by building blocks and driving modes. We design a new self-assembly method based on the magnetic coupling between spin-polarized electrons. First-principles calculations show that spinpolarized electrons from different endohedral metallofullerene(EMF) superatoms can pair each other to ensure a one-dimensional extending morphology. Furthermore, without ligand passivation, the EMF superatoms maintain their electronic structures robustly in self-assembly owing to the core-shell structure and the atomic-like electron arrangement rule. Therefore, it should noted that the magnetic coupling of monomeric electron spin polarization can be an important driving mechanism for high-precision self-assembly. These results represent a new paradigm for self-assembly and offer fresh opportunities for functional material construction at the atomic level. 相似文献
18.
V. K. Kalevich A. Yu. Shiryaev E. L. Ivchenko A. Yu. Egorov L. Lombez D. Lagarde X. Marie T. Amand 《JETP Letters》2007,85(3):174-178
Conduction-electron spin polarization dynamics achieved by pulsed optical pumping at room temperature in GaAs1−x
N
x
alloys with a small nitrogen content (x = 2.1, 2.7, and 3.4%) is studied both experimentally and theoretically. It is found that the photoluminescence circular polarization
determined by the mean spin of free electrons reaches 40–45% and this giant value persists within 2 ns. Simultaneously, the
total free-electron spin decays rapidly with the characteristic time ≈ 150 ps. The results are explained by spin-dependent
capture of free conduction electrons on deep paramagnetic centers resulting in the dynamical polarization of bound electrons.
A nonlinear theory of spin dynamics in the coupled system of spin-polarized free and localized carriers has been developed
which describes the experimental dependencies, in particular, the electron spin quantum beats observed in a transverse magnetic
field.
The text was submitted by the authors in English. 相似文献
19.