Imperfect Polarization Research Articles

Influences of Imperfect Polarization Induced Effects to the Quasi-Reciprocal Reflective Optical Voltage Sensor

The influences of imperfect polarization induced effects are investigated in this paper for a novel optical voltage sensor (OVS), which consists of quasi-reciprocal reflective optical interferometer and digital closed-loop detection scheme. The numerical models are established to describe the relationship between the characteristic parameters of imperfect polarization and the performances of the OVS, which is also simulated to investigate quantitatively. The numerical models and the simulated results are experimentally verified with typical imperfect polarization induced errors. Accordingly, the primary characteristic parameters of imperfect polarization are illuminated. What's more, the conclusions of this paper can provide useful references for the design and performance improvement of the novel Pockels effect based OVS.

Polarization metrology: Alignment of polarizing prisms in optical polarization systems

A new simple and precise method for the alignment of polarizing prisms in optical polarization systems is presented. The Poincaré sphere representation is used to explain the alignment procedure. The method considers the case of an imperfect polarizer and is applicable to both transmission and reflection polarization systems.

Dynamical Suppression of Unwanted Transitions in Multistate Quantum Systems

We propose a method to suppress unwanted transition channels and achieve perfect population transfer in multistate quantum systems by using composite pulse sequences. Unwanted transition paths may be present due to imperfect light polarization, misalignment of the quantization axis, spatial inhomogeneity of the trapping fields, off-resonant couplings, etc., or they may be merely unavoidable, e.g., due to perturbing excitations in molecules and solids. Compensation of separate or simultaneous deviations in polarization, pulse area, and detuning is demonstrated, even when these deviations are unknown, in three-state V and Ξ (ladder) systems and in a four-state Y system.

Temperature‐resolved photoluminescence of nonpolar InGaN/GaN multiple quantum well heterostructures grown on LiAlO2

AbstractPolarized photoluminescence (PL) of a series of m ‐plane InGaN/GaN multiple quantum well heterostructures (xIn = 5‐30%) was measured in a wide temperature range (T = 10‐580 K). A pronounced S‐shape behaviour of PL band position was observed for all samples which is an evidence of a high degree of localization of photogenerated carriers. From temperature dependences of the PL degree of polarization, the energy difference between the two highest valence subbands ΔE in InGaN was estimated to be increasing from ∼70 meV to ∼160 meV with rising indium content from 5% to 30%. The high‐temperature spectral difference between the polarized PL components was substantially lower than ΔE which is caused by imperfect polarization of optical transitions to different valence subbands. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Rapid and Robust Spin State Amplification

Electron and nuclear spins have been employed in many of the early demonstrations of quantum technology. However, applications in real world quantum technology are limited by the difficulty of measuring single spins. Here we show that it is possible to rapidly and robustly amplify a spin state using a lattice of ancillary spins. The model we employ corresponds to an extremely simple experimental system: a homogenous Ising-coupled spin lattice in one, two, or three dimensions, driven by a continuous microwave field. We establish that the process can operate at finite temperature (imperfect initial polarization) and under the effects of various forms of decoherence.

Attenuation characterization of multiple combinations of imperfect polarizers

Malus's law, when used to calculate the attenuation ratio of the combination of two imperfect polarizers (two-CIP), will introduce an error, especially near the crossed-axis orientation. In this paper, first, the Jones matrix of the imperfect polarizer is deduced and an exact algorithm of the attenuation ratio of the two-CIP is proposed as well as its monotonic attenuation interval. Experimental results confirm that our deduced expression is more accurate than Malus's law. Then based on this algorithm, an attenuation-ratio expression of the combination of three imperfect polarizers (three-CIP) is presented. In this three-CIP model, it is found that when the electric field amplitude ratio of the imperfect polarizer is epsilon, the attenuation ratio can change from 1 to epsilon(4) monotonically in a general model when P(1) and P(3) are rotated and P(2) is fixed, which is proved by experiment. Finally, it is deduced that the combination of n imperfect polarizers (n-CIP) can obtain a minimum attenuation ratio of epsilon(2(n-1)), which indicates the number of imperfect polarizers needed to achieve the required attenuation ratio.

Feasibility of satellite quantum key distribution

In this paper, we present a novel analysis of the feasibility of quantum key distribution between a LEO satellite and a ground station. First of all, we study signal propagation through a turbulent atmosphere for uplinks and downlinks, discussing the contribution of beam spreading and beam wandering. Then we introduce a model for the background noise of the channel during night-time and day-time, calculating the signal-to-noise ratio for different configurations. We also discuss the expected error-rate due to imperfect polarization compensation in the channel. Finally, we calculate the expected key generation rate of a secure key for different configurations (uplink, downlink) and for different protocols (BB84 with and without decoy states, entanglement-based Ekert91 protocol).

Product decomposition of measured Mueller matrices from the FLC based NIR Mueller Matrix Ellipsometer

AbstractThis paper reports on the application of the first near‐infrared spectroscopic Mueller Matrix Ellipsometer (MME) based on Ferro‐electric Liquid Crystal retarders (FLC) and fixed waveplates. Operation of the instrument is demonstrated by transmission Mueller matrix measurements, and product decomposition of an imperfect dichroic polarizer and a depolarizing rough glass surface. The decomposition of the measured matrices is qualtitatively discussed in terms of retardance, diattenuation, depolarization, and azimuthal orientation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Development of Spin-Polarized Ion Scattering Spectroscopy

Spin-polarized ion scattering spectroscopy using an electron-spin-polarized 4He+ ion beam was developed as a novel analytical method of the element selective spin state at outermost surfaces. Spin-polarized He+ ions were generated from the Penning ionization of metastable He 2(3)S1 atoms (He*), which were spin-polarized by optical pumping (OP). The spin polarization of He* (PHe*) was observed to be the highest with an OP radiation density of about 0.05 W cm(-2), and a further increase of the OP radiation density reduced P(He*). This decrease of PHe* is attributed to imperfect polarization of the OP radiation, hence optimization of the OP radiation density is essential to obtain He+ ions with high spin polarization. As a result of this optimization, we successfully observed the spin dependence of the scattered He+ ion yield on an Fe(100) surface exposed to an oxygen atmosphere.

Single Spin Measurement Using Cellular Automata Techniques

We analyze a conceptual approach to single-spin measurement. The method uses techniques from the theory of quantum cellular automata to correlate a large number of ancillary spins to the one to be measured. It has the distinct advantage of being efficient: under ideal conditions, it requires the application of only O((3)square root N)) steps (each requiring a constant number of rf pulses) to create a system of N correlated spins. Numerical simulations suggest that it is also, to a certain extent, robust against pulse errors, and imperfect initial polarization of the ancilla spin system.

Errors of Mueller matrix measurements with a partially polarized light source

The linear errors of Mueller matrix measurements, using a partially polarized light source, have been formulated for imperfections of misalignment, depolarization, and nonideal ellipsometric parameters of the polarimetric components. The error matrices for a source-polarizer system and a source-polarizer-compensator system are derived. A polarized light source, when used with an imperfect polarizer, generates extra errors in addition to those for an unpolarized source. The compensator redistributes these errors to different elements of the error matrix. The errors of the Mueller matrices for the polarizer-sample-analyzer and the polarizer-compensator-sample-analyzer systems are evaluated for a straight through case. This error analysis is applied to a Stokes method and an experiment was performed to show the errors by a polarized light source. This general analysis can be used to evaluate errors for ellipsometry and polarimetry.

Velocity map imaging study of OCS photodissociation followed by S(1S) autoionization at 157 nm

Atomic sulphur ions (S+) were observed directly by crossing a carbonyl sulphide (OCS) molecular beam with a F2 laser. In this study both S+ ion and electron images were measured using the velocity map imaging technique. The results imply that S+ is produced from the well-known photodissociation of OCS at 157 nm leading to the dominant S(1S) + CO(1Σ+) channel, and then the excited S(1S) atom is directly ionized by another 157 nm photon. Correlated vibrationally resolved angular distributions and internal energy distribution of the CO coproducts are reported here and compared with previous studies. This experiment yields strong and sharp S+ images which may be useful for calibrating any imaging or laser ionization apparatus when using a 157 nm laser. A number of technical aspects such as corrections for partial slicing and imperfect laser polarization are described. ion of product angular distributions using both polarized and unpolarized photolysis lasers is also demonstrated using velocity map imaging.

Refractive Index Measurements of Films with Biaxial Symmetry. 2. Determination of Film Thickness and Refractive Indices Using Polarized Transmission Spectra in the Transparent Wavelength Range

A technique is formulated to determine both thickness and refractive indices of free-standing films with biaxial symmetry from polarized transmission spectra. The films must be transparent and show little dispersion in refractive indices in the wavelength range where the transmission spectra are collected. Methods are proposed to correct the errors caused by imperfect polarization of incident radiation and thickness variation across the sampling area. Anisotropic refractive indices and thickness of poly(biphenyl dianhydride-p-phenylenediamine) films which exhibit uniaxial optical anisotropy are determined from polarized transmission spectra. The refractive index and thickness values compare well to those obtained from waveguide prism coupler and profilometer measurements.

Error models for long-distance Qubit teleportation

A recent proposal for realizing long-distance, high-fidelity qubit teleportation is reviewed. This quantum communication architecture relies on an ultrabright source of polarization-entangled photons plus a pair of trapped-atom quantum memories, and it is compatible with long-distance transmission over standard telecommunication fiber. Models are developed for assessing the effects of amplitude, phase, and frequency errors in the entanglement source, as well as fiber loss and imperfect polarization restoration, on the throughput and fidelity of the system.

Spectral responsivity of various types of silicon photodiode at oblique incidence: comparison of measured and calculated values

The spectral responsivity of several types of silicon photodiode at oblique incidence (approximately 45 degrees) is investigated. Both windowless diodes and diodes that incorporate quartz windows are considered. The spectral responsivities are measured directly for both parallel and perpendicular polarized radiation. For comparison, the responsivity at oblique incidence is also calculated from the normal-incidence measured responsivity in conjunction with the reflectance values at normal and oblique incidence calculated from thin-film theory by use of the measured oxide thicknesses of the diodes and published data on the refractive indices of silicon and fused silica. A technique, believed to be novel, is described for accurately measuring the oxide thicknesses of the diodes. A comparison of calculated and measured responsivity values shows that, when imperfect polarizers are used, it may be more accurate over a certain spectral range to calculate the responsivities at oblique incidence rather than to measure them directly. The additional uncertainty associated with the calculated responsivity values at oblique incidence, with respect to the original source data for normal incidence, is +/-1% over a wide spectral range.

Polarization Lidar: Correction of instrumental effects

An algorithm for correcting instrumental effects in polarization lidar studies is discussed. Cross-talk between the perpendicular and parallel polarization channels and imperfect polarization of the transmitted laser beam are taken into account. On the basis of the Mueller formalism it is shown that - with certain assumptions - the combined effects of imperfect polarization of the transmitted laser pulse, non-ideal properties of transmitter and receiver optics and cross-talk between parallel and perpendicular polarization channels can be described by a single parameter, which is essentially the overall system depolarization.

Generation of circularly polarized high-order harmonics by two-color coplanar field mixing

An efficient method is investigated for the generation of circularly polarized high-order harmonics by a bichromatic laser field whose two components with frequencies $\ensuremath{\omega}$ and $2\ensuremath{\omega}$ are circularly polarized in the same plane, but rotate in opposite directions. The generation of intense harmonics by such a driving-field configuration was already confirmed by a previous experiment. With the help of both a semiclassical three-step model as well as a saddle-point analysis, the mechanism of harmonic generation in this case is elucidated and the plateau structure of the harmonic response and their cutoffs are established. The sensitivity of the harmonic yield and the polarization of the harmonics to imperfect circular polarization of the driving fields are investigated. Optimization of both the cutoff frequency and the harmonic efficiency with respect to the intensity ratio of the two components of the driving field is discussed. The electron trajectories responsible for the emission of particular harmonics are identified. Unlike the case of a linearly polarized driving field, they have a nonzero start velocity. By comparison with the driving-field configuration where the two components rotate in the same direction, the mechanism of the intense harmonic emission is further clarified. Depending on the (unknown) saturation intensity for the bichromatic field with counter-rotating polarizations, this scheme might be of practical interest not only because of the circular polarization of the produced harmonics, but also because of their production efficiency.

X-ray dichroism in biaxial gyrotropic media: Differential absorption and fluorescence excitation spectra

The differential absorption and the differential change in the polarization state of an X-ray beam propagating inside a gyrotropic crystal are described using a 4 X 4 Muller matrix, the 16 elements of which are related to the anisotropic components of the multipolar polarizability tensors at the absorbing site. Analytical expressions are given up to third order for X-ray linear and circular dichroism, X-ray optical rotation and X-ray circular polarimetry in transmission. The same formalism is extended to discuss Fluorescence detected dichroism spectra with or without polarization analysis of the fluorescence. Fluorescence detected dichroism is strictly proportional to dichroism measured in the transmission geometry only for uniaxial crystals. In biaxial crystals, the tiny effects of X-ray gyrotropy are swamped by large linear dichroism signals due to the imperfect polarization transfer function of Bragg monochromators. Second order effects should also be taken into consideration. Our general formulation of linear and circular dichroism includes terms of odd parity with respect to the action of the time reversal operator: such terms cannot contribute to natural dichroism but can be activated by a magnetic field. The terms responsible for X-ray magnetic circular dichroism are well known but non-reciprocal X-ray gyrotropy effects are also predicted in magnetic crystals of appropriate symmetry.

Polarization Sagnac interferometer with a common-path local oscillator for heterodyne detection

We describe a free-space common-path polarization Sagnac interferometer. The polarization Sagnac interferometer is used in a symmetric fashion with detection on the dark fringe of the interference to avoid photodetector saturation when high-powered illumination is used. By modulating the carrier field that is reflected from the interferometer, we generate a local oscillator for heterodyne detection of the signal field. We calculate the effect of optical element misalignments and imperfect polarization on the shot-noise–limited sensitivity of the interferometer. The predictions are experimentally verified with a 2-m arm-length tabletop polarization Sagnac interferometer.

Analysis of imperfect polarizer effects in magnetic rotation spectroscopy

Small amounts of ellipticity in the nominally linearly polarized light used in magnetic rotation spectroscopy play an important role in determining the character of the signals developed in these experiments. For example, ellipticity introduced by stress-induced birefringence can easily influence such signals more than does a nonzero polarizer extinction ratio. In addition, for nearly-crossed polarizers, an initial ellipticity allows one to probe magnetic circular dichroism instead of the more commonly investigated magnetic circular birefringence. A general expression for the magnetic rotation spectroscopy signal is derived and compared to experimental results. An expression for the detection sensitivity is developed by taking shot noise and rms laser power uctuations to be the dominant noise sources.