Amplitude and phase control of attosecond light pulses

We report the generation, compression, and delivery on target of ultrashort extreme-ultraviolet light pulses using external amplitude and phase control. Broadband harmonic radiation is first generated by focusing an infrared laser with a carefully chosen intensity into a gas cell containing argon atoms. The emitted light then goes through a hard aperture and a thin aluminum filter that selects a 30-eV bandwidth around a 30-eV photon energy and synchronizes all of the components, thereby enabling the formation of a train of almost Fourier-transform-limited single-cycle 170 attosecond pulses. Our experiment demonstrates a practical method for synthesizing and controlling attosecond waveforms.     

Propagation of circularly polarized light in media with large-scale inhomogeneities

Small-angle multiple scattering of circularly polarized waves in disordered systems composed of large (larger than the light wavelength) spherical particles is discussed. The equation for Stokes’s fourth parameter V — the difference between the intensities of the left-and right-hand polarized light — is shown to have the form similar to that of the scalar transport equation for intensity I, the only difference being the presence of an additional “non-small-angle” term responsible for depolarization. In the case of small-angle scattering, depolarizing collisions are relatively rare and, in contrast to the scalar case, the problem contains an additional spatial scale, namely the depolarization depth. The polarization degree and helicity of the scattered light are calculated for the case of purely elastic scattering and in the presence of absorption in the medium. For strong absorption, depolarization is shown to follow the transition to the asymptotic regime of wave propagation. The features appearing in strong (non-Born) single scattering are also discussed. Zh. éksp. Teor. Fiz. 115, 769–790 (March 1999)     

Propagation of polarized light in media with large discrete inhomogeneities

An approximate analytical method of solution of the vector radiative-transfer equation for an optically isotropic medium with large-scale inhomogeneities is proposed. The method is based on an assumption about the distinct anisotropy of single scattering. The method was used to calculate the polarization characteristics of light multiply scattered in a monodisperse medium with large spherical particles.     

Polarization anisotropy of optical transmission in opals and Langmuir-Blodgett crystals

The transmission spectra of thin-film colloidal photonic crystals with three-dimensional and one-dimensional-two-dimensional photonic energy band structures, i.e., opals and Langmuir-Blodgett crystals with a refractive index contrast of ∼1.5: 1.0, have been measured in linearly polarized light. It has been demonstrated that the polarization anisotropy in the light transmitted through the crystal is uniquely related to the diffraction resonance and that the degree of polarization can exceed 90%. A higher degree of polarization is provided by lattices that are characterized by a smaller attenuation of light polarized in the plane of incidence. It has been revealed that the diffraction resonances from the crystal planes for which the dispersions are in anticrossing with the dispersion of the growth planes acquire the same anisotropy. The general character of the results obtained has been confirmed by the fact that the polarization anisotropy identically manifests itself in colloidal crystals that have different symmetries and lattice orderings.     

Thomas rotation and polarized light: A non-abelian geometric phase in optics

We describe anon-abelian Berry phase in polarization optics, suggested by an analogy due to Nityananda between boosts in special relativity and the effect of elliptic dichroism on polarized light. The analogy permits a simple optical realization of the non-abelian gauge field describing Thomas rotation. We also show how Thomas rotation can be understood geometrically on the Poincaré sphere in terms of the Pancharatnam phase.     

Bragg diffraction of light in synthetic opals

Three-dimensional light diffraction from the crystal structure, formed by closely packed a-SiO₂ spheres of submicron size, of samples of synthetic opals was visualized. The diffraction pattern of a monochromatic light beam was established to consist of a series of strong maxima whose number and angular position depend on the wavelength and mutual orientation of the incident beam and the crystallographic planes of the sample. The diffraction patterns were studied under oblique incidence on the (111) growth surface of the sample and with light propagated in the (111) plane in various directions perpendicular to the sample growth axis. The spectral and angular relations of diffracted intensity were studied in considerable detail in both scattering geometries. The experimental data are interpreted in terms of a model according to which the major contribution to the observed patterns is due to Bragg diffraction of light from (111)-type closely packed layers of the face-centered cubic opal lattice. The model takes into account the disorder in the alternation of the (111) layers along the sample growth axis; this disorder gives rise, in particular, to twinning of the fcc opal lattice.     

Spectral features of polarized light absorption and anisotropy of a local field in the D ho discotic

The polarized IR absorption spectra of monodomain planar-oriented films of a discotic liquid crystal D _ho are obtained for the first time. The spectral effects induced by the resonance dipole-dipole interaction of molecules, which have been predicted earlier, were observed. It was found that molecular excitations in isotropic and liquid-crystal phases are mixed due to local-filed effects and this mixing affects the relative intensity and dichroism of the absorption bands. New methods were suggested for measuring the local-field parameters in the D _ho phase from intensities and positions of the polarized absorption bands taking into account the mixing of molecular excitations. The two-dimensional crystal lattice of molecular columns was shown to reduce the local-field anisotropy of this phase.     

Optical properties of polarization-dependent geometric phase elements with partially polarized light

The behavior of geometric phase elements illuminated with partially polarized monochromatic beams is investigated both theoretically and experimentally. The element discussed in this paper is composed of wave plates with π-retardation and a space-variant orientation angle. We found that a beam emerging from such an element comprises two polarization orders; right-and left-handed circularly polarized states with conjugate geometric phase modification. This phase equals twice the orientation angle of the space-variant wave plate comprising the element. Apart from the two polarization orders, the emerging beam coherence polarization matrix includes a “vectorial interference matrix” which contains information concerning the correlation between the two orthogonal, circularly polarized portions of the incident beam. In this paper we measure this correlation by a simple interference experiment. In addition, we found that the equivalent mutual intensity of the emerging beam is modulated according to the geometric phase induced by the element. Other interesting phenomena concerning propagation will be discussed theoretically and demonstrated experimentally. The experiment made use of a spherical geometric phase element that was realized by use of a space-variant subwavelength grating illuminated with CO₂ laser radiation of 10.6 μm wavelength.     

Selective control of light beams in diffraction experiments on synthetic opals

This paper reports on an experimental and theoretical investigations of the possibility of selectively controlling the intensity of {hkl} diffraction reflections in synthetic opals. The calculations of the photonic stop-band width for low-contrast multi-component photonic crystals argue for a selective pattern of the vanishing of various {hkl} stop bands (and, accordingly, of the various {hkl} diffraction reflections) under variation of the dielectric permittivity of one of the components. Optical diffraction patterns have been studied visually and recorded in various scattering geometries with bulk opal samples illuminated by white unpolarized light. The experiments have made use of immersion spectroscopy, a method reducing essentially to successive measurements of diffraction patterns under variation of the dielectric permittivity of the liquid filler of the opal matrix. The {111} and {220} Bragg reflections have been observed to weaken noticeably at the filler permittivities matching very well with the values derived earlier from an analysis of transmission spectra.     

Residual polarization of non-coherently backscattered linearly polarized light: the influence of the anisotropy parameter of the scattering medium

The effect of preservation of the residual polarization of backscattered light in the case of multiply scattered disordered media illumination by a linearly polarized plane wave is examined using the path-integral approach and Monte Carlo simulation. Disordered ensembles of non-interacting dielectric particles are considered as the model of scattering media. The influence of the anisotropy parameter of the scattering system on the degree of residual polarization is analysed. Experimental results obtained for various scattering systems at different wavelengths of illuminating light are in satisfactory agreement with the results of theoretical analysis and Monte Carlo simulation. The dependence of statistical properties of the polarization states of backscattered field partial components, such as probability distributions of ellipticity, on the anisotropy parameter is studied.     

Propagation of light through a monolayer of particles: Analysis of phase and coherent transmittance

Phase variations of a wave transmitted through a monolayer of spherical scatterers are studied as functions of size, optical constants, and particle concentration for light incident normally to the surface of the layer. The analysis is performed in the quasi-crystal approximation of the theory of multiple scattering of waves and in the single scattering approximation. The results obtained allow one to estimate the limits of applicability of the single scattering approximation to layers with partial ordering of scatterers in analysis of the transmitted wave phase. The variations of the phase of the wave in the range of the parameters where the coherent component of the transmitted beam exhibits quenching are studied. It is shown that small variations in the refractive index of the particles may give rise to strong variations of the phase. This effect can be used for phase modulation of light beams, e.g., in liquid crystal films controlled by an electric (or magnetic) field.     

线性偏振光激发的错位表面等离子体激元纳米结构聚焦

利用扫描近场光学显微镜观测并分析了两种表面等离子体激元纳米结构对表面等离子体激元(SPP)的激发和聚焦现象.用线偏振光照射有半个周期相位差的环状沟槽结构与有半个周期位相差的环状狭缝结构,得到了单点的SPP聚焦.有限时域差分法的模拟结果验证了实验中观测的现象.这两种相位错位的表面等离子体激元纳米结构,突破了由于干涉导致的线偏振光不能得到单个聚焦点的限制.与采用径向偏振光激发而得到单个聚焦点的方法相比,线偏振光不需要聚焦,也不需要将光束中心对准纳米结构的几何中心即可得到单点聚焦。     

Polarization squeezing in polarized light

It is shown that polarized light can be polarization squeezed only if it exhibits sub-Poissonian statistics with the Mandel's Q factor less than − 1/2.     

Modern description of polarized light: matrix methods

Problems involving the calculation of the passage of a polarized light beam through a succession of polarizing devices are often difficult and tedious. These may be simplified if modern methods of describing polarized light are used, namely the Stokes and Jones vectors, the Mueller and Jones calculi and the coherency matrix formalism. In this paper these concepts are presented and the vectors for various states of polarized light and the matrices of polarizers and retardation plates are given, together with examples of their method of use.     

获得偏振光的方法

介绍了用反射、折射及干涉等方法获得线偏振光、椭圆偏振光和圆偏振光的方法 ,并从原理、实验及生产工艺等方面进行了说明     

Amplitude and phase of light scattered by micro-scale aggregates of dielectric spheres: Comparison between theory and microwave analogy experiments

Light scattering is a useful diagnostic tool for characterization of particles. Direct scattering measurements for arbitrarily shaped micro-scale particles is difficult due to small-scale limitations. Microwave analogy is a convenient approach to realize such measurements as it enables realization of analogous experiments with larger model particles in a spectral domain where wavelengths are on centimeter scale. In the present study a test model analogous to light scattering by a micro-scale aggregate of dielectric spheres was constructed and experimentally characterized in the microwave regime. Measured amplitude and phase of the scattered field were compared with theoretical predictions obtained from quasi-exact multiple-scattering T-matrix method and discrete dipole approximation (DDA). Excellent agreement demonstrates the validities of both the experiment and the models.     

Amplitude and phase clipping: Strehl ratio versus divergence

We consider the transverse characteristics of a Gaussian laser beam subject to a phase or amplitude clipping due to a pupil which is a π-plate or an opaque disc (stop). In particular, we consider the correlation between two features, the Strehl ratio and divergence angle, usually used for characterising the focusability of a diffracted beam. It is demonstrated that the Strehl ratio does not give systematically a global view, from a divergence point of view, on the transverse properties of a Gaussian beam suffering amplitude or phase diffraction. In addition, we consider the case of self-diffraction of a Gaussian beam upon a Gaussian phase aberration of same width, and it is found that the on-axis intensity describes correctly the whole diffracted beam cross-section, from a divergence point of view, only if the central phase shift is smaller than π. Another example showing that the focusability of a pure high-order Laguerre–Gauss TEM_p0 beam, free from any clipping, cannot be correctly described by Strehl ratio is also considered.