Showing papers on "Optical polarization published in 1995"

Principles of Nonlinear Optical Spectroscopy

Abstract: 1. Introduction 2. Quantum Dynamics in Hilbert Space 3. The Density Operator and Quantum Dynamics in Liouville Space 4. Quantum Electrodynamics, Optical Polarization, and Nonlinear Spectroscopy 5. Nonlinear Response Functions and Optical Susceptibilities 6. The Optical Response Functions of a Multilevel System with Relaxation 7. Semiclassical Simulation of the Optical Response Functions 8. The Cumulant Expansion and the Multimode Brownian Oscillator Model 9. Fluorescence, Spontaneous-Raman and Coherent-Raman Spectroscopy 10. Selective Elimination of Inhomogeneous Broadening Photon Echoes 11. Resonant Gratings, Pump-Probe, and Hole Burning Spectroscopy 12. Wavepacket Dynamics in Liouville Space The Wigner Representation 13. Wavepacket Analysis of Nonimpulsive Measurements 14. Off-Resonance Raman Scattering 15. Polarization Spectroscopy Birefringence and Dichroism 16. Nonlinear Response of Molecular Assemblies The Local-Field Approximation 17. Many Body and Cooperative Effects in the Nonlinear Response

Gamma-ray pulsars: emission zones and viewing geometries

Abstract: There are now a half-dozen young pulsars detected in high-energy photons by the Compton Gamma-Ray Observatory (CGRO), showing a variety of emission efficiencies and pulse profiles We present here a calculation of the pattern of high-energy emission on the sky in a model which posits gamma-ray production by charge-depleted gaps in the outer magnetosphere This model accounts for the radio to gamma-ray pulse offsets of the known pulsars, as well as the shape of the high-energy pulse profiles We also show that about one-third of emitting young radio pulsars will not be detected due to beaming effects, while approximately 25 times the number of radio-selected gamma-ray pulsars will be viewed only high energies Finally we compute the polarization angle variation and find that the previously misunderstood optical polarization sweep of the Crab pulsar arises naturally in this picture These results strongly support an outer magnetosphere location for the gamma-ray emission

Polarized reflectance of bare soils and vegetation: measurements and models

Abstract: This paper presents a large set of spectral and directional signatures of the polarized reflectance acquired over various surfaces. Two analytical physically-based models were developed, one for bare soils and the other for simple vegetation cover. They consider that the polarized reflectance is generated by single specular reflection over isotropically distributed facets or leaves. The models accurately reproduce the order of magnitude and the directional signature of the reflectance for view angles of up to ~ 5 5 "I.t confirms that specular reflection is the main process that generates polarization over natural surfaces. Polarized light generated by other processes, and that are not accounted for by the models, can be observed however in the backscattering direction where single specular reflection does not yield polarization. Although spectral variations in the polarized reflectance are observed, they are explained by atmospheric effects on the direct solar beam. The atmospheric correction yields a surface polarized reflectance which is larger than the model estimate, but is still on the same order of magnitude. For the simple canopies studied, our results suggest that, except for particular events such as the "heading" of a canopy, vegetation will generate little variability in the polarized reflectance making this information unsuitable for monitoring of the canopies. On the other hand, since the models accurately predict the polarized reflectance from the surface, they can be used to correct airborne or spaceborne polarized reflectance measurements when the inversion of aerosol parameters is attempted.

Multiconfigurational self-consistent reaction field theory for nonequilibrium solvation

Abstract: We present multiconfigurational self‐consistent reaction field theory and implementation for solvent effects on a solute molecular system that is not in equilibrium with the outer solvent. The approach incorporates two different polarization vectors for studying the influence of the solvent. The solute, an atom, a molecule or a supermolecule, is assumed to be surrounded by a linear, homogeneous medium described by two polarization vector fields, the optical polarization vector and the inertial polarization vector fields. The optical polarization vector is always in equilibrium with the actual electronic structure whereas the inertial polarization vector is not necessarily in equilibrium with the actual electronic structure. The electronic structure of the compound is described by a correlated electronic wave function—a multiconfigurational self‐consistent field (MCSCF) wave function. This wave function is fully optimized with respect to all variational parameters in the presence of the surrounding polariz...

Radio properties of narrow-lined Seyfert 1 galaxies

Abstract: We have observed seven narrow-linedd Seyfert 1 (NLS1) galaxies and one high-ionization Seyfert 2 galaxy with the Very Large Array (VLA). Combining these observations with published data, we summarize the radio properties of the NLS1 galaxies for which spectropolarimetry was reported by Goodrich. Fifteen of these 17 objects now have published radio observations of high sensitivity, and only nine of those have been detected. For a Hubble parameter of 75 km/s/Mpc, the 6 cm radio powers range from 10(exp 20) to 10(exp 23) W/Hz, within the range previously found for other types of Seyfert galaxy. The median radio size of the nine VLA-detected galaxies is no larger than 300 pc, similar to the median size found by Ulvestad & Wilson for a distance-limited sample of Seyfert galaxies. Of the six NLS1 galaxies known to have significant intrinsic optical polarization, three have measurable radio axes. Two of those three galaxies have radio major axes close to 90 deg from their polarization position angles, while the third has an inner radio axis that may be nearly parallel to the polarization position angle. The former relationship is expected for a Seyfert 1 in a unified model of Seyfert galaxies, assuming no intrinsic continuum polarization.

A new short and low-loss passive polarization converter on InP

Abstract: We propose an improved polarization converter in InGaAsP-InP. It contains a series of waveguide sections with asymmetric cross-sections with angled facets. A 09-mm-long TE/TM-converter at a wavelength of 1.5 /spl mu/m is simulated. It contains 10 sections and has an excess loss of 0.25 dB. Both coupled mode theory and beam propagation method (BPM) simulations are included. >

Optical polarization of molecules

Abstract: 1. Angular momentum and transition dipole moment 2. Excited state angular momenta distribution 3. Ground state angular momenta polarization 4. Effect of external magnetic field on angular momenta distribution 5. General equations of motion for arbitrary J values 6. Other methods of alignment and orientation of molecules Appendix References Index.

In situ spectroscopic ellipsometry to monitor the process of TiNx thin films deposited by reactive sputtering

Abstract: In situ spectroscopic ellipsometry (SE) in the energy region from 1.5 to 5.5 eV was used to monitor the process of TiNx films deposited by dc reactive magnetron sputtering of Ti. The dielectric function e(ω) measured by SE yields the optical response of TiNxfilms and valuable information on their structural characteristics that are also verified by electron microscopy observations. The plasma energy of TiNx was found to depend strongly on the stoichiometry of the material and therefore is a valuable parameter for in situ monitoring of TiNx stoichiometry. Analysis of the e(ω) spectra of the TiNx films deposited in sequential layers by an effective medium theory provides precious information about the initial stages of growth, the composition, the deposition rate, and any change in film growth.

Operational system for quantum cryptography

Abstract: An operational system for quantum cryptography based on the polarisations of single photons has been demonstrated. The system allows the automated transmission of secure messages between two computers at data rates up to 5 kHz with lower error rates than previous systems.

Theoretical analysis of birefringence and form‐induced polarization mode dispersion in birefringent optical fibers: A full‐vectorial approach

Abstract: A new numerical method for analyzing birefringence and dispersion characteristics of birefringent optical fibers is presented. A major advantage of the method, based on the solution of full‐vectorial Maxwell equations, is its high accuracy no matter how great the geometrical anisotropy of the optical fiber. To verify the reliability of our numerical procedure, the modal birefringence and the form‐induced polarization mode dispersion in elliptical core fibers with different eccentricities are investigated and their values compared with some theoretical and experimental results.

Quantitative analysis of DNA orientation in stationary AC electric fields using fluorescence anisotropy

Abstract: In this study, micro-fabricated electrodes are used to obtain stationary field in excess of 1 MV/m. Micro-electrodes with either 15 /spl mu/m or 60 /spl mu/m gap, depending on the length of sample DNA to be used, are fabricated with planar technique on glass substrates. Because the high-field region in the gap is small and having high surface to volume ratio, Joule heat is efficiently removed, so that very high intensity field can be created without excessive temperature rise. A high-sensitive detection method is required for the measurements with micro-electrodes, due to a small number of molecules involved. For this purpose, a fluorescent dye is intercalated into the bases of DNA, and the optical polarization of emitted fluorescence is measured. The polarization components of the emitted light, both parallel and perpendicular to the applied electrostatic field, are measured independently, and fluorescent anisotropy, the ratio of (the difference between parallel and perpendicular polarization) to (total emission) is used as the index of DNA orientation. Field-intensity dependence of fluorescence anisotropy is measured using pUC18 (2.7 kb DNA), and the result is compared with an analytical model. The measured polarization factor is found to be several orders of magnitude larger than that of a conducting ellipsoid with the same dimension. This can be explained by assuming a 'swelling' of electrical equivalent diameter of DNA by 20 nm, comparable to the Debye length, i.e. the thickness of counter ion cloud. The amount of counter ion is varied by changing pH of the medium, keeping its conductivity constant. As pH increases, increase in the anisotropy is observed, in particular between pH 5 and 6. This is attributed to the dissociation of phosphate groups, by which negative charge density on the DNA backbone is increased. Multivalent cations, Ca/sup 2+/, Mg/sup 2+/, Zn/sup 2+/ and Al/sup 3+/, are expected to bind to DNA backbone and reduce polarization. However, no significant change of anisotropy is observed in the concentration range of 10/sup -4/-10/sup -6/ in our experimental conditions. Further increase in concentration was prevented by conductivity increase.

Tapered acoustical directional couplers for integrated acousto-optical mode converters with weighted coupling

Abstract: Weighted coupling for strong sidelobe suppression of integrated acoustooptical mode converters in LiNbO/sub 3/ using acoustical directional couplers has been studied theoretically and experimentally. A parameter free model for the propagation of surface acoustic waves in guiding structures has been developed based on a step-like variation of the acoustic velocity. Comparisons of theoretical results with experimental ones for acoustic waveguides and directional coupler structures confirm the applicability of the model. A coupled mode description of the acousto-optical polarization conversion in converters with acoustical directional couplers has been developed and applied to several tapered acoustical directional couplers. The model reveals that the conversion characteristics are usually strongly asymmetric. If the directional coupler is appropriately designed, a sidelobe suppression of about 30 db can be achieved. First experimental results with tapered directional couplers confirm within some limits the theoretical predictions. >

Polarization control of vertical-cavity surface-emitting lasers through use of an anisotropic gain distribution in [110]-oriented strained quantum-well structures

Abstract: An analysis of the in-plane optical matrix elements connected with the gain distribution of (In,Ga)As-GaAs quantum-well structures on [110] GaAs substrates is presented. The in-plane gain distribution is found to be anisotropic-with a maximum directed along the [110]-[110] crystallographic axis. Optically-pumped vertical-cavity surface-emitting lasers on the [110] surface with these quantum wells in the cavity exhibit stable, well-defined polarization states; this stability is believed to be a consequence of the predicted anisotropic gain distribution on the [110] surface. Of the two orthogonal eigen polarizations observed, the one with the higher optical intensity, for a given pump power, was found to be stabilized along the [110] crystallographic axis; this is in agreement with the analysis. >

Structural and optical properties of annealed proton‐exchanged waveguides in z‐cut LiTaO3

Abstract: The structural properties of annealed proton‐exchanged waveguides in z‐cut LiTaO3 have been investigated. Observations made in a polarizing microscope together with infrared‐absorption measurements indicate the formation of monoclinic Li(1−x)HxTaO3 after proton exchange in pure pyrophosphoric acid. This monoclinic phase disappears after annealing at 300 °C. High‐resolution x‐ray diffraction shows that the c lattice parameter is 0.57% larger in the exchanged layer than in the bulk. During annealing the c parameter relaxes and in addition there appears a second diffraction peak in the x‐ray rocking curves. This peak is attributed to α‐phase Li(1−x)HxTaO3. A model for the increase of the refractive index is suggested. It shows that the main reason for the difference in index increase between proton‐exchanged waveguides in LiTaO3 and LiNbO3 is the stronger spontaneous polarization of LiNbO3. The model predicts an increase of the refractive index of LiTaO3 after annealing which is experimentally observed. A sh...

Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. 3: Ground-based observations in 1991 November

Abstract: We present ground-based observations of the BL Lac object PKS 2155-304 during 1991 November. These data were obtained as part of a large international campaign of observations spanning the electro-magnetic spectrum from the radio waves to the X-rays. The data presented here include radio and UBVRI fluxes, as well as optical polarimetry. The U to I data show the same behavior in all bands and that only upper limits to any lag can be deduced from the cross-correlation of the light curves. The spectral slope in the U-I domain remained constant on all epochs but 2. There is no correlation between changes in the spectral slope and large variations in the total or polarized flux. The radio flux variations did not follow the same pattern of variability as the optical and infrared fluxes. The polarized flux varied by a larger factor than the total flux. The variations of the polarized flux are poorly correlated with those of the total flux in the optical (and hence UV domain; see the accompanying paper by Edelson et al.) nor with those of the soft X-rays. We conclude that the variability of PKS 2155-304 in the optical and near-infrared spectral domains are easier to understand in the context of variable geometry or bulk Lorentz factor than of variable electron acceleration and cooling rates.

Spectral signal processing in intrinsic interferometric sensors based on birefringent polarization-maintaining optical fibers

Abstract: The straightforward spectral signal processing technique is applied in intrinsic strain, temperature and distributed linear position interferometric fiber optic sensors based on birefringent polarization maintaining fibers. The method provides nonincremental absolute measurements of external physical parameter affecting the sensing fiber. Simultaneous interrogation of sensors in a network is demonstrated. >

Optical properties of stretched polymer dispersed liquid crystal films: Angle-dependent polarized light scattering

Abstract: A systematic experimental study of the polarization-dependent light scattering properties of uniaxially stretched polymer dispersed liquid crystal (PDLC) films with the bipolar director field structure in the micron-sized nematic droplets is presented. The space distribution of the scattered intensity as a function of the incident and scattered optical polarization, as well as the degree and azimuth of polarization of the scattered light have been measured, and the results are discussed in terms of physical parameters related to the sample structure, such as molecular alignment, droplet size, shape, orientation, etc. The main factors determining the light polarizing ability of an ordered PDLC film are discussed. On the basis of the results obtained, some potential display applications of a stretched PDLC film are proposed. In particular, the reasons are given for using such a film as a polarizing diffuser for backlit twisted nematic LCDs.

10 Gbit/s four-channel wavelength- and polarisation-division multiplexing transmission over 340 km with 0.5 nm channel spacing

Abstract: The authors propose a novel WDM transmission technique combined with polarisation-division multiplexing (PDM) which doubles the frequency utilisation efficiency. This technique is used to transmit a 10 Gbit/s four-channel WDM signal with 0.5 nm channel spacing over 340 km and the signal is demultiplexed using an optical filter having 0.5 nm FWHM and a polarisation beamsplitter.

Massively parallel electromagnetic simulation for photolithographic applications

Abstract: The two-dimensional massively parallel electromagnetic simulation program TEMPEST has been generalized to extend its applicability to many of the difficult problems in photolithography, metrology, and alignment. TEMPEST, which has been made available on the NCSA and other computing centers, combines together techniques for analysis of the transverse electric (TE) and the transverse magnetic (TM) polarizations, oblique incidence, highly dispersive materials, and a technique for synthesis of partially coherent optical images. The solution is based on the time-domain finite-difference method, but exploits the power of massively parallel computer architectures. Equations suitable for massively parallel implementation are given for oblique incidence, both polarizations and dispersive materials. Computer time per iteration cycle is constant irrespective of the polarization and angle of incidence. However, the total simulation time for convergence was found to be dominated by physical scattering phenomena. Convergence for the TM polarization is 1.5 times slower than the TE polarization because of edge currents, and oblique incidence is 2 times slower than normal incidence owing to artificial reflection from the domain boundaries. A typical simulation time is three to five minutes with 256 k (1 k=1024) simulation nodes on a CM-2 with 8 k processors. The effectiveness of the program for photolithographic applications is demonstrated by considering the effects of subtle changes in phase-shifting mask topography on the optical images. >

A prototype clamp-on magneto-optical current transducer for power system metering and relaying

Abstract: A new type of Faraday effect based magneto-optical current transducer (MOCT) has been developed. This paper presents the theoretical background, engineering design, and test results of this clamp-on MOCT. The sensor consists of two separate clamp-on parts. This design avoids the need to break the current carrying circuit in order to have the conductor enclosed by the optical path. A feedback scheme has been designed to stabilize the light source. The MOCT has two output stages, 1 kA and 20 kA, so that it can provide current signals for both power system metering and relaying devices, The theoretical background of maintaining the light travelling through the glass prism to be linearly polarized and the analysis on the effects of dielectric and metal reflections on the linearly polarized light is presented in the appendix. >

High signal-to-noise ratio birefringence-compensated optical delay line based on a noise-reduction scheme

Abstract: A multichannel fiber-optic delay-line architecture based on optical polarization switching is proposed that uses non-polarization-maintaining optical fibers. Critical birefringence-compensation and noise-reduction techniques are introduced and demonstrated for these delay lines, which show a high optical polarization extinction ratio (>39 dB) and a high electrical signal-to-noise ratio (>92 dB).

Trellis coded polarization shift keying modulation for digital optical communications

Abstract: The application of the well-known technique of trellis coded modulation to coherent optical communications using polarization shift keying (POLSK) is described and analyzed. The resulting receiver is formed by a front-end which performs the heterodyne detection and the Stokes parameter extraction, cascaded with an electronic Viterbi processor operating the maximum likelihood estimate of the transmitted sequence. Results in terms of the error event probability using optimum as well as a simpler suboptimum branch metric show power gains of the order of 3-4 dB, at the expense of a reasonable increase in complexity, only concerning the processing in the electronic domain. These coding gains are not lost even in the presence of high levels of phase noise, to which POLSK in general is highly insensitive. >

Performance of coherent optical polarization shift keying modulation in the presence of phase noise

Abstract: The performance of optical coherent modulation schemes using the state of polarization of light as the modulating parameter (POLSK, POLarization Shift Keying) is analyzed, in the presence of laser phase noise. First, we compare three different analysis methods to account for the effects of phase noise in the binary case, and choose the one offering the best trade-off in terms of accuracy/complexity. Successively, we derive a tight upper bound to the performance of multilevel POLSK systems with postdetection filtering. Then, we include phase noise using the best method as tested in the binary case and extensively discuss the performance of binary and various multilevel POLSK constellations, optimized with respect to the IF filter bandwidth. The results show that binary POLSK has a very low sensitivity to phase noise and that multilevel POLSK is even less sensitive than the binary scheme. >

Vibration immunity for optical-fiber current measurement

Abstract: Optical-fiber measurement of electric current can be rendered immune from the effects of environmental vibration by utilizing the nonreciprocity of the Faraday effect in an arrangement which propagates light simultaneously in the two directions around a fiber loop enclosing an electric current. The system is compared with a back-reflection arrangement. Temperature variations are also suppressed. >

New Polydiene Side-Chain Liquid Crystalline Polymers. Synthesis and Microstructure

Abstract: Novel side-chain liquid crystalline polymers were synthesized based on the molecular design of the chemical structures of main-chain, spacer, and mesogenic groups. The main-chain structure is polydiene by the radical polymerization of diene derivatives with a mesogenic group. Spacer groups are not only oligomethylene but also those containing a siloxane or ether linkage. The stereochemistry of the main chain, elucidated by 1 H NMR, 13 C NMR, DEPT, and NOESY spectroscopies, is principally (E)-1,4 (cis concerning the carbon-carbon main chain). The polymers take the smectic liquid crystalline state with cyanobiphenyl, fluorobiphenyl, or alkoxybiphenyl as a mesogen. The transition temperatures of polymers with a spacer having a siloxane linkage are lower than those with hexamethylene as a spacer. Cooling the polymer with 4-(hexyloxy)biphenyl as a mesogen and siloxane linkage in the spacer seems to result in the change of the phase which is evidenced by the change in the optical polarization micrograph.

Friction model of Photo-induced Reorientation of Optical Axis in Photo-oriented Langmuir-Blodgett Films

Abstract: A model of the Photo-induced Optical Anisotropy (POA) is proposed for molecular films consisting of ordered domains. The model describes the molecular motion in an anisotropic molecular field at different rates of collisions (friction) between, respectively, excited and ground state molecules and a substrate under polarized light illumination into a molecular absorption band. It is shown that if an angular distribution function of domain molecules has a non-zero width, the different friction coefficients would result in domain director rotation. At low light intensity, these different frictions could be due to three processes: i) change in molecular conformation, ii) change in molecular interaction and iii) local recrystallisation. The domain director rotation is considered as a result of the conservation of the angular momentum for the whole system, which includes the substrate. A new method, based on double illumination of photo-oriented films, is proposed to observe the light-induced optical axis rotation. Experimental results concerning photo-induced rotation of the optical axis in photo-oriented Langmuir-Blodgett films are presented and explained by the model. The angular dependence of the photo-induced angular torque is confirmed. The existence of an angular threshold for out-for-plane rotation (θ-rotation) is demonstrated and qualitatively explained by anchoring of molecular layers with the substrate.