Polarized fusion

Since more than 50 years it has been discussed to increase the gain of nuclear fusion reactors with the use of polarized fuel. For example, the total cross sections of the fusion reactions d + t → ⁴He + n or ³He + d → ⁴He + p are increased by a factor of about 1.5 if the spins of both incoming particles are aligned. But before polarized fuel can be used for energy production in the different types of reactors, a number of questions must be answered. In this contribution we give an overview on our various activities in this field of research.     

Polarized light

Following the recent work of Chandleret al on quasi probability distributions for spin-1/2 particles, we show that polarized light can be interpreted in terms of trivariate probability distributions in two different ways by choosing the variates to correspond to (i) the co-ordinates on the Poincare sphere, (ii) the components of the spin operator of the photon. In either case, it is shown that the Margenau-Hill procedure leads to probability mass functions while the Wigner-Weyl approach leads to probability density functions and the well-known Stokes parameters are also realised as appropriate averages with respect to these distribution functions.     

Polarized electron sources

We review current methods for production of polarized electron beams. Major focus is devoted to photoemission from GaAs, which is the way that current facilities rely on. Some aspects of this kind of technology such as the physics behind generation of polarized beams and its advantages and limitations are considered. Finally, the perspectives for implementation of a GaAs photocathode in a RF gun are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Polarized Spacetime Foam

An approximate model of a spacetime foam is presented. It is supposed that in the spacetime foam each quantum handle is like to an electric dipole and therefore the spacetime foam is similar to a dielectric. If we neglect of linear sizes of the quantum handle then it can be described with an operator containing a Grassman number and either a scalar or a spinor field. For both fields the Lagrangian is presented. For the scalar field it is the dilaton gravity + electrodynamics and the dilaton field is a dielectric permeability. The spherically symmetric solution in this case give us the screening of a bare electric charge surrounded by a polarized spacetime foam and the energy of the electric field becomes finite one. In the case of the spinor field the spherically symmetric solution give us a ball of the polarized spacetime foam filled with the confined electric field. It is shown that the full energy of the electric field in the ball can be very big.     

圆偏振光和线偏振光在正常色散材料中的时空自压缩

实验研究了圆偏振和线偏振高强度飞秒激光脉冲在正常色散材料中传输时的时空自压缩现象。实验中利用BK7玻璃作为正色散材料,比较研究了不同偏振入射情况下脉冲波形及频谱的变化规律。圆偏振光入射时,可以获得更短脉冲宽度的压缩脉冲和更窄的光谱宽度。在圆偏振光入射条件下,50 fs入射脉冲成功地自压缩到了19 fs,获得了大于2.5倍的压缩倍率。所以利用圆偏振光可以获得更短压缩脉冲,更大能量,更好光束质量的激光。     

Polarized absorption spectra of diphenylnitroxide

A polarization study of the low-lying electronic states of the diphenylnitroxide radical imbedded in a benzophenone single crystal is presented. Assignments are made for the first two electronic excited states: ${}^2\text{B}{}_2\text{(n → π}{}^1\text{)}$ at 569 nm and ${}^2\text{B}{}_1\text{(π → π}{}^1\text{)}$ at 431 nm. Vibronic coupling is invoked in inducing the $\text{n → π}{}^1$ transition. The electronic structure of the nitroxide bears some resemblance to the corresponding carbonyl. The delocalization of the π electrons is also discussed.     

Distribution Function of Polarized Proton

The region of allowed values of quark and gluon spin densities in a proton is discussed. The helicity difference distributions of the constituents which can fit the existent data for g₁^p are constructed and the significant differences between the results fiom our distributions and from other models at small x region (< 10^-1) are shown.     

Polarized photofluorescence excitation spectroscopy

When a triatomic molecule ABC is photolysed by a beam of light to produce the fragments AB and C, the directional nature of the photo-dissociation process manifests itself in a number of ways; in particular, the angular distribution of each fragment is anisotropic, and the angular momentum vector J of the AB photofragment points in space with a preferential distribution with respect to the direction of the light beam. If the AB diatomic fragment is electronically excited, then the emission from AB* will, in the absence of collisions, be polarized, and a measurement of the degree of polarization, p, will provide information about the symmetry nature and dissociation dynamics of the photoexcited state (ABC)*. A number of limiting cases are presented for the sign and magnitude of p, calculated in the classical high J limit, following dissociation of both linear and bent triatomic molecules.     

Polarized confocal theta microscopy

We propose a comprehensive treatment of theta microscopy based on dipole emission, which better describes fluorescence emission than the isotropic emission model, as fluorescence emission is often polarized. Formulas describing the point spread function for polarized confocal fluorescence theta microscopy are given. Examples are given and some advantages of polarized theta fluorescence microscopy are presented. To cite this article: O. Haeberlé et al., C. R. Physique 3 (2002) 1445–1450.     

Polarized parton densities updated

We present a new next-to-leading order (NLO) QCD analysis of the world data on inclusive polarized deep inelastic scattering. A new set of polarized parton densities is extracted from the data and the sensitivity of the results to the newly incorporated SLAC/E155 proton data is discussed.     

Polarized superfluorescent fiber source

We report the demonstration of a polarized superfluorescent fiber source (SFS) that increases the power output in the desired linearly polarized component by a factor of 1.76 over that of a standard, unpolarized SFS that uses the same pump power. This increase in efficiency is accomplished by insertion of a low-loss polarizer at an optimum point in the erbium-doped fiber of a standard SFS.     

Creation of Super Long Transversely Polarized Optical Needle Using Azimuthally Polarized Multi Gaussian Beam

The intensity distribution in the focal region of a high-NA lens for the incident azimuthally polarized multi Gaussian beam transmitted through a multi belt spiral phase hologram is studied on the basis of the vector diffraction theory.Here we report a new method used to generate a needle of transversely polarized light beam with sub diffraction beam size of 0.366λ that propagates without divergence over a long distance of about 22λ in free space.We also expect that such a light needle of transversely polarized beam may find its applications in utilizing optical materials or instruments responsive to the transversal field only.     

Polarized fluorescence of monoanions of Zn-octaethylphlorin

We investigate the luminescent properties (radiation spectrum, polarized spectrum) of the monoanions of Zn-octaethylphlorin, which is an intermediate product of the reduction, reaction of porphyrins. An oscillator model is presented that includes three electronic oscillators, with a long-wave one being oriented perpendicularly to the remaining two. The lifetime of the excited singlet state τ=30±15 nsec is estimated. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 329–332, May–June, 1997.     

Polarized ARPES spectra of undoped cuprates

The spectral density (SD) in the ARPES spectra of antiferromagnetic (AFM) dielectrics Sr₂CuO₂Cl₂ and Ca₂CuO₂Cl₂ along the principal symmetry directions of the Brillouin zone was studied by the generalized tight binding method. At the valence band top of these undoped cuprates in the AFM state, there is a pseudogap of magnetic nature with E _s(k)～0–0.4 eV between a virtual level and the valence band proper. The observed similarity of dispersion along the Γ-M and X-Y directions can be explained by the proximity of the ³ B _1g triplet and the Zhang-Rice singlet levels. The value of parity of the polarized ARPES spectra at the Γ, M, and X points calculated for the AFM phase of undoped cuprates with an allowance for the partial contributions is even. The conditions favoring observation of the partial contributions in polarized ARPES spectra are indicated. Due to the spin fluctuations, the virtual level acquires dispersion and possesses a small spectral weight. Probably, this level cannot be resolved on the background of the main quasi-particle peak as a result of the damping effects.     

海洋气溶胶多光谱偏振特性研究

为提高海洋气溶胶的反演精度,定量研究了气溶胶在可见近红外波段的多光谱偏振辐射特性。首先建立了合理的海洋气溶胶及海面模型,基于逐次散射法准确模拟了光在气溶胶中及大气—海洋交界面处的矢量辐射传输过程,接着从光谱角度定量分析了典型波段处的反射率和偏振反射率,在此基础上提出了海洋气溶胶偏振辐射的光谱分布模型,并用卫星数据对模型进行验证,最后研究了气溶胶光学厚度、观测角度、海水叶绿素a浓度和海面风速对气溶胶多光谱偏振辐射的影响。研究表明,在可见近红外波段不考虑大气吸收和耀斑效应时,气溶胶偏振辐射的光谱变化符合幂函数模型;在不同波段处,海洋气溶胶的偏振辐射受海水叶绿素a浓度和海面风速的影响不同;海洋气溶胶的多光谱偏振辐射信息有效体现了气溶胶的自身特性,且与反射率相比,偏振反射率随各因素的变化存在更明显的谱段差异性。因此,可以运用气溶胶的多光谱偏振信息反演海洋气溶胶参数,多光谱探测的加入对提高气溶胶反演精度具有重要意义。