Polarization optimization in the interference of four umbrellalike symmetric beams for making three-dimensional periodic microstructures

A systematic and comprehensive analysis of the interference of four umbrellalike beams (lFUB) is provided based on the reciprocal space theory. The concept of pattern contrast is extended to the case of the IFUB, and it is indicated that a uniform contrast for all the interference terms can be obtained by properly choosing the beam ratio and the polarization of each beam. Different polarization combinations, including linear light and linear light, circular light and circular light, and linear light and circular light, have been discussed for the purpose of maximum uniform contrast. It is shown that the use of circular light may generally improve the uniform contrast. This study may lay a theoretical foundation for holographic fabrication of three-dimensional (3D) periodic microstructures, such as simple cubic, body-centered cubic, face-centered cubic, or trigonal lattice.     

Formation of three-dimensional periodic microstructures by interference of four noncoplanar beams

A newly reported method of making three-dimensional microstructures or photonic crystals by holographic lithography has some obvious advantages over other techniques with the same purpose. A systematic and comprehensive analysis of interference of four noncoplanar beams (IFNB) is provided. It shows that all 14 Bravais lattices can be formed by means of IFNB and gives explicit relationships between each lattice and the corresponding recording geometry. The concept of pattern contrast is extended to the case of IFNB, and it is indicated that a uniform contrast for each interference term can be obtained by properly choosing the beam ratio and polarization. A calculation algorithm is then developed to optimize the direction of polarization of each beam to ensure maximum uniform contrast. These results, verified by computer simulations, may lay a theoretical foundation for fabrication of photonic crystals with the approach of IFNB.     

Time Reversal for the Polarization State in Optical Systems

Abstract

The time-reversal operator for the polarization state can be successfully implemented in any optical system where a beam retraces its path. A Faraday rotator followed by a mirror realizes a device whose representative matrix is similar to the quantum mechanics time-reversal operator for the spin. Any effect of the medium birefringence is cancelled and, for linear polarization, the beam always returns opposite polarized with respect to the entrance state. Analogies with the operation of a phase-conjugation mirror are pointed out and suggested consequences of the novel optical configuration are given.     

Refractive Bessel lattice in azobenzene liquid crystal

A refractive Bessel lattice with micrometric periodicity is induced optically in a photosensitive azobenzene liquid crystal cell of 3?µm thickness by a green 532?nm, 30?mW Bessel beam and with simultaneous illumination by a red 632.8?nm, 15?mW Gaussian beam. The uninterrupted action of both beams plays a key role in the complete mechanism of the refractive lattice formation. The lattice formation is investigated in real-time by the measurement of forward diffracted ring powers from both the red Gaussian and the green Bessel beams. The diffraction efficiency is investigated depending on the green Bessel beam intensity and on the mutual relation between the green beam polarization and the rubbing direction of the cell. A maximum diffraction efficiency of 1.1% is obtained which corresponds to a refractive index change of 6?×?10^?3. Simulations are performed and a physical model to explain the experimental results is discussed.     

Review of finite-element characterization of photonic devices

Abstract

We report the development and applications of finite-element-based numerical approaches for the characterization of a wide range of photonic devices. The full-vectorial finite-element method is considered for the modal solutions of uniform guided-wave sections and the least-squares boundary residual method is used to calculate the scattering coefficients for butt-coupled uniform waveguide sections. Several guided-wave components are discussed and their operating characteristics are illustrated. Particular emphasis is given to key photonic components such as the spot-size converters, Bragg gratings, polarization splitters, polarization rotators, multimode interference-based devices and modulators. Valuable results relating to the design and characterization of these important photonic components are presented.     

Bilayer Coatings for Light Refraction Without Change of Polarization

Abstract

Wave refraction without change of polarization at a dielectric—dielectric interface is achieved with a bilayer coating of two transparent thin films. For given refractive indices of all media, the thicknesses of the two films are determined as functions of the angle of incidence. The polarization-independent reflectance and the differential reflection phase shift of the coated substrate are also calculated. Examples are presented of MgF₂—ZnS and Ge—MgF₂ bilayer coatings on a Ge substrate that refract infrared radiation without change of polarization. Such coatings are useful in the construction of polarization-preserving beam deflectors and beam splitters.     

A new class of electrostatic systems which keep plane homogeneous charged-particle beams exactly parallel

An analysis is made of electrostatic systems whose field is formed by two superposed two-dimensional fields with a common plane of symmetry (midplane). It is assumed that these fields overlap in the region where a charged particle beam propagates. The main property of these systems is that they conserve ideally (without angular aberrations) the parallelism of a charged particle beam of uniform energy-to-charge ratio, propagating in the midplane of the field. This new class of electrostatic system includes the four-electrode system given as an example in which each electrode consists of four plates positioned symmetrically relative to the midplane. Pis’ma Zh. Tekh. Fiz. 24, 57–61 (October 12, 1998)     

Direct observation of microscopic plastic deformation of stainless steel using lattice drawn by focused ion beam of Ga+

Abstract

Visualisation of the microscopic deformation of a stainless steel was attempted. A mirror polished, flat surface specimen was subjected to a simple tension test, and the deformation of a fine lattice drawn by a focused ion beam (FIB) of Ga⁺ was observed. The depth of the lattice was of the order of a few tens of nanometres. The penetration depth of Ga⁺ was estimated using SRIM software, and the result indicated that the use of a FIB might not cause serious detriment to the mechanical properties of the lattice surface. After testing, lattices were examined by field emission scanning electron microscopy (FESEM). The results showed that displacement was continuous in the grain as well as across the grain boundary, and the microscopic deformation was categorised into three patterns: (a) a clear thin layer of shear deformation which was discontinuous across the grain boundary, (b) an area of uniform deformation inside this thin layer and (c) microscopic shear bands appearing sporadically in the grains.     

Optical heterodyne detection of random electromagnetic beams

Abstract

In this paper we present a general analysis for the optical heterodyne detection of random electromagnetic beams. To describe the ensemble of quasimonochromatic beams which are partially polarized and partially coherent, we use a recently developed matrix treatment. We derive an expression for the signal-to-noise ratio (SNR) in terms of the beam coherence polarization matrices of the beams on the detector surface. Numerical examples are given for the SNR variation in the case of partially polarized Gaussian Schell model beams and the optimum detection is discussed in terms of beam parameters of the local oscillator.     

Novel Polarimetric Technique Exploring Spatiotemporal Birefringent Response of an Anti-ferroelectric Liquid Crystal Cell

Abstract

This paper describes a novel polarimetric technique for mapping the spatiotemporal birefringent parameters characterizing an anti-ferroelectric liquid crystal cell. A linearly polarized beam of light transmitted by the liquid crystal cell turns into an elliptically polarized beam. Some birefringent irregularities existing over the cell make state of polarization of the elliptically polarized beam of light be spatiotemporal. This beam works as a signal beam to interfere with a reference beam consisting of two orthogonal linearly polarized components. The resultant interference pattern is taken by a charge-coupled device video camera and recorded in a computer. The computer gives the information required for determining the spatiotemporal birefringent parameters that characterize the liquid crystal cell. The major advantage is that the two-dimensional distribution of the birefringent axes as well as the two principal refractive indices can be determined simultaneously, and no use of any optical components for polarization alignment makes it possible to follow a rapid change in birefringent parameters within the maximum frame rate of the video camera. A change in time-dependent birefringent parameter is measured at every 0·1 ms for the demonstration experiment.     

Polarization separation of light in holographic grating reflection in conical mounting

Abstract

We experimentally investigate the interaction of linearly polarized light with a holographic grating in a conical mounting. Due to the periodic structure, the polarization properties of the reflected zeroth-order beam are highly sensitive to the conical angle. When a focused Gaussian beam with linear polarization impinges on an air–grating interface at an exceptional conical angle, a spatial splitting of the reflected beam is observed behind a polarizer. We find that it can be interpreted using the anisotropy of the polarization distribution in holographic grating reflection.     

Polarization recording of holograms in partially polarized recording light

A theoretical approach is considered for media whose scalar and anisotropic responses are of opposite sign. The nondiffracted beam, and the imaginary and real images formed by a polarization hologram are analyzed under these conditions. It is shown that the imaginary image has its polarization transformed compared with the object field while a pseudoscopic object field reconstructed in terms of polarization state and degree is formed in the real image. Pis’ma Zh. Tekh. Fiz. 23, 38–42 (February 12, 1997)     

Coherent quantum measurement for the direct determination of the degree of polarization and polarization mode dispersion compensation

Abstract

An example of a coherent measurement for the direct evaluation of the degree of polarization of a single-mode optical beam is presented. It is applied to the case of great practical importance where depolarization is caused by polarization mode dispersion. It is demonstrated that coherent measurement has the potential of significantly increasing the information gain, compared to standard incoherent measurements.     

Method for Birefringence Measurements with Correction of Errors Due to Multiple Reflection in Anisotropic Plates

Abstract

Birefringence measurements of anisotropic plates using coherent light are affected by errors due to the multiple reflections in the investigated plate. An evaluation method for measuring birefringence is presented, where the intensity distributions of two light beams are used for the correction of these errors. These beams arise from a polarizing beam splitter, which is the analyser of the polarization system. In this paper, a theoretical treatment is given which shows that this method results in more accurate values than the usual methods, especially for highly refractive materials with a small birefringence.     

Extremely narrowed spontaneous emission spectrum induced by elliptically polarized light

Abstract

We demonstrate the control of spontaneous emission from a five-level atom embedded in a modified reservoir under the action of a single control beam with elliptical polarization. For different initial-state preparations, we take into account the influence of the phase difference between the two circularly polarized components of the control beam on the behavior of spontaneous emission. For the ground initial states, the spontaneous emission spectrum usually shows ultranarrow central lines which are greatly enhanced. In contrast, for the excited initial states, these enhanced ultranarrow lines are significantly suppressed due to the destructive quantum interference. Furthermore, our numerical simulations indicate that the multipeak structure appears in the presence of the elliptically polarized control beam and external magnetic field. Such a scheme for controlling spontaneous emission may find applications in high-precision spectroscopy.     

Elastodynamic Response of a Periodic Layer of Spherical Particles Containing Vacancies

Abstract

This paper is concerned with the influence of vacancies on the elastodynamic response of a periodic (square) array of identical spherical elastic inclusions embedded in an unbounded elastic matrix. A response function of the array is defined as H?(ω) ≡ R?(ω)/T?(ω), where R?(ω) and T?(ω) are, respectively, the reflection and transmission spectra of the lattice. H?(ω) was measured for a “perfect lattice,” i.e., one without any vacancies, and was found to be characterized by lattice resonances. H?(ω) was also measured for lattices containing one and three vacancies within the 72 lattice site area insonified by the ultrasonic beam. A counter-intuitive observation is that the presence of even one vacancy significantly reduces the amplitude of the fundamental lattice resonance. Furthermore, in the case of the specimen containing three closely spaced vacancies, the reduction is not three times the reduction due to one vacancy; it is significantly less than that.     

Spontaneous formation of arrays of three-dimensional islands in epitaxial layers

An analysis is made of a theoretical model of the formation of three-dimensional nanometer-size islands in molecular beam epitaxy. The kinetics of the self-organization processes are described using a lattice gas model of the adsorbate with self-consistent allowance for lateral interactions in the activation energies of the diffusion processes. It is shown that at below-critical temperatures in a certain range of thicknesses, decay of the spatially uniform state gives rise to arrays of three-dimensional nano-islands which do not participate in the coalescence process after growth has ceased. The average size of the islands, their geometric profile, and the spatial ordering depend strongly on the kinetic parameters of the model. Pis’ma Zh. Tekh. Fiz. 24, 20–26 (July 12, 1998)     

Kurtosis parameter K of arbitrary electromagnetic beams propagating through non-Kolmogorov turbulence

General analytical formulae for the kurtosis parameters K (K parameters) of the arbitrary electromagnetic (AE) beams propagating through non-Kolmogorov turbulence are derived, and according to the unified theory of polarization and coherence, the effect of degree of polarization (DOP) of an electromagnetic beam on the K parameter is studied. The analytical formulae can be given by the second-order moments and fourth-order moments of the Wigner distribution function for AE beams at source plane, the two turbulence quantities relating to the spatial power spectrum, and the propagation distance. Our results can also be extended to the arbitrary beams and the arbitrary spatial power spectra of Kolmogorov turbulence or non-Kolmogorov turbulence. Taking the stochastic electromagnetic Gaussian Schell-model (SEGSM) beam as an example, the numerical examples indicate that the K parameters of a SEGSM beam in non-Kolmogorov turbulence depend on propagation distance, the beam parameters and turbulence parameters. The K parameter of a SEGM beam is more sensitive to effect of turbulence with smaller inner scale and generalized exponent parameter. A non-polarized light has the strongest ability of resisting turbulence (ART), however, a fully polarized SEGSM beam has the poorest ART.     

Orientation of biological cells using plane-polarized gaussian beam optical tweezers

Abstract

Optical tweezers are widely used for the manipulation of cells and their internal structures. However, the degree of manipulation possible is limited by poor control over the orientation of the trapped cells. We show that it is possible to controllably align or rotate disc-shaped cells—chloroplasts of Spinacia oleracea—in a plane-polarized Gaussian beam trap, using optical torques resulting predominantly from circular polarization induced in the transmitted beam by the non-spherical shape of the cells.     

Levelling the focal spot intensity of the focused gaussian beam

Abstract

It is experimentally and numerically shown that a simple binaryphase optical element can be used for levelling the light energy in the focal plane of the focused Gaussian beam, generating a square-shaped focal beam, and transforming the Gaussian beam into a uniform beam which preserves its radius at a definite length of its path.