Showing papers on "Optical polarization published in 1976"

Multicomponent photopolymer systems for volume phase holograms and grating devices.

Abstract: Novel photopolymer systems for the fabrication of high-resolution volume phase holograms and grating devices are reported. Previously reported techniques use a single monomer (or a mixture of similar monomers) and rely solely on density modulation. In contrast, we have found it advantageous to use a mixture of components chosen to have differing reactivities and polarizabilities, which results in a composition modulation. During the image-forming exposure the more reactive monomer is polymerized while the less reactive species is excluded from the irradiated regions. Two-way diffusion, which must be invoked to explain our results, leads to a modulation of the chemical composition and hence of the polarizability of the final material. In some systems the polarizability effect was strong enough to exceed the density effect, even when these factors were in opposite directions. As in previous systems, an over-all exposure is used to fix the images. With appropriate monomer systems, stable images were obtained even when one component was unreactive. The peak-to-peak refractive index differentials achieved in our systems were as high as 1.5%. This is an order of magnitude larger than that reported for initially all liquid systems and 50% larger than that reported for related solid materials. The use of a liquid system enables us to fill small cavities with our materials and then record a high-resolution image. We have made gratings of >3000 lines mm(-1) inside hollow fibers, with 80 microm i.d., filled with a photopolymer material. For white light guided in the core, the expected band-stop filter response was observed.

Submillimeter laser wavelength tables

Abstract: Tables are presented that list submillimeter laser lines observed in the optical pumping of molecular gases with CO2 laser radiation. The lines have been obtained from previous publications by various authors and are in the wavelength range from 34 μm to 1.965 mm. One table lists, for each gas, the submillimeter wavelengths observed, the line of the CO2 pump laser, references to the literature, and, where available, the polarization and power of the submillimeter laser and the power of the CO2 pump laser. A second table lists all the observed laser wavelengths in numerical order together with the gas in which each line was observed. These tables should be useful to researchers working with submillimeter lasers.

Performance limitations imposed on optical waveguide switches and modulators by polarization

Abstract: Crosstalk in optical waveguide switches/modulators caused by having two polarizations simultaneously present is studied in this work. This situation is expected to arise when fiber optical transmission lines are coupled to integrated optical circuits. Modulator/switch performance is found to be strongly affected by having two propagating polarizations. Conditions on device design are found that minimize the polarization sensitivity of switches/modulators, making them suitable for use with fiber optic transmission lines.

Nonrelativistic Compton scattering and models of quasars

Abstract: In order to avoid the problems associated with electron synchrotron models of quasar visible and infrared radiation, we propose a nonrelativistic Compton scattering model. Calculations of the emergent flux from such models produce power-law spectra with a wide range of spectral indices. An analogy to reactor theory is pointed out. Fluctuation and polarization behavior resembling that observed is predicted. Possible ranges of parameters and their constraints are discussed, but no attempt is made to construct a detailed model of any individual object. (AIP)

Multiple scattered radiation emerging from Rayleigh and continental haze layers. 1: Radiance, polarization, and neutral points.

Abstract: The matrix operator method was used to calculate the polarization of radiation scattered on layers of various optical thicknesses, with results compared for Rayleigh scattering and for scattering from a continental haze. In both cases, there are neutral points arising from the zeros of the polarization of single scattered photons at scattering angles of zero and 180 degrees. The angular position of these Rayleigh-like neutral points (RNP) in the sky shows appreciable variation with the optical thickness of the scattering layer for a Rayleigh phase matrix, but only a small variation for haze L phase matrix. Another type of neutral point exists for non-Rayleigh phase functions that is associated with the zeros of the polarization for single scattering which occurs between the end points of the curve. A comparison of radiances calculated from the complete theory of radiative transfer using Stokes vectors with those obtained from the scalar theory shows that differences of the order of 23% may be obtained for Rayleigh scattering, while the largest difference found for a haze L phase function was of the order of 0.1%.

Quantum-mechanical phase interference and optical polarization in low- energy Na$sup +$-Ne inelastic collisions

Abstract: Pronounced oscillatory structure and strong optical polarization effects have been observed in emission cross sections for the production of optical radiation measured as a function of energy in low-energy (100 eV to 6 keV) Na$sup +$-Ne atomic collisions. Highly regular oscillatory structure found in the energy dependence of the emission cross sections for ten Ne I(3p $Yields$ 3s) optical transitions is observed to be in antiphase with similar structure in two Na I(3p $Yields$ 3s) optical emission cross sections. In addition, large polarization effects have been observed in optical radiation from excited J not- equal 0 states. In one particular case involving a J = 1 to J = 0 transition, oscillations in the excitation function appear to arise exclusively from the polarization component of the radiation perpendicular to the beam direction. These observations indicate strong sublevel-state selection processes associated with collisional quantum-mechanical phase-interference phenomena. A simple model is presented which allows us to uniquely determine for the first time the quasimolecular states responsible for such oscillatory structure and consequently associated with each polarization component. Analysis based on the model for the case of the more » Na* (3p) radiation data indicates that the oscillatory structure is not attributable to interactions between simple single-electron diabatic states as believed previously. Similar analysis of the Ne* (3p) radiation data uniquely identifies the $sup 1$Pi ($Omega$ = +- 1) and $sup 3$Pi ($Omega$ = +- 2) molecular states as the major contributors. (AIP) « less

Analysis and design of semileaky-type thin-film optical waveguide isolator

Abstract: This paper describes an optical waveguide isolator that utilizes the unidirectional guided-radiation mode coupling in a magnetooptic/anisotropic slab guide. The basic structure is the semileaky-type waveguide that has been previously used as a polarization mode filter. Specific features of the proposed device are its compact one-section form resulting from the inherent polarization-discrimination property and the relaxed dimensional tolerance due to the automatic phase-matching of coupled modes. Design data and a related discussion are given for the example of LiNbO 3 /YIG/GGG layered structure operating in the 1.15-μm-wavelength region.

Asymptotic radiance and polarization in optically thick media: ocean and clouds.

Abstract: Deep in a homogeneous medium that both scatters and absorbs photons, such as a cloud, the ocean, or a thick planetary atmosphere, the radiance decreases exponentially with depth, while the angular dependence of the radiance and polarization is independent of depth. In this diffusion region, the asymptotic radiance and polarization are also independent of the incident distribution of radiation at the upper surface of the medium. An exact expression is derived for the asymptotic radiance and polarization for Rayleigh scattering. The approximate expression for the asymptotic radiance derived from the scalar theory is shown to be in error by as much as 16.4%. An exact expression is also derived for the relation between the diffusion exponent k and the single scattering albedo. A method is developed for the numerical calculation of the asymptotic radiance and polarization for any scattering matrix. Results are given for scattering from the haze L and cloud C3 distributions for a wide range of single scattering albedos. When the absorption is large, the polarization in the diffusion region approaches the values obtained for single scattered photons, while the radiance approaches the value calculated from the expression: phase function divided by (1 + kμ), where μ is the cosine of the zenith angle. The asymptotic distribution of the radiation is of interest since it depends only on the inherent optical properties of the medium. It is, however, difficult to observe when the absorption is large because of the very low radiance values in the diffusion region.

New map of the optical polarisation of galaxy M82

Abstract: M82 is the nearest galaxy evidently containing a strong central source of energy, which is possibly similar to the nucleus of a Seyfert galaxy, and this seems to have given rise to an unusual explosive event1. The appearance of M82 is that of a flattened irregular system seen nearly edge-on, and if a distinct nucleus exists, it is highly obscured2 at optical wavelengths. Compact radio features are, however, present, and complex resolved radio and infrared sources and bright visible H II regions occupy an area ∼ 12″×35″ in the centre of the galaxy. The outer parts of the galaxy show linear optical polarisation, discovered by Elvius3. This is thought to arise from reflection in an extensive halo of dust particles of the light of the bright nucleus (or nuclear region) and of the galactic disk (for a recent discussion, see ref. 4). Consequently, observation of the polarisation can give information about the position and luminosity of the energetic nuclear region, and about the scattering medium. Outstanding questions about M82 involve the existence and nature of a compact nucleus and the morphological and evolutionary state of the whole galaxy.

A quasi-optical polarization-independent diplexer for use in the beam feed system of millimeter-wave antennas

Abstract: The theory and performance of a quasi-optical Fabry-Perot diplexer employing two rectangular meshes and capable of polarization-independent operation at large angles of incidence are presented. The diplexer is suitable for use in a dual-polarization dual-frequency beam feed system for millimeter-wave antennas. An experimental diplexer operating at an angle of incidence of 56.5\deg \pm 1\deg was found to separate two 1.1-GHz bands centered at 21 and 31.5 GHz with a loss of less than 0.3 dB in either band and a cross-polarization discrimination of more than 40 dB in the higher band and 30 dB in the lower band.

Comments on the dispersion relations for the complex refractive index of circularly and elliptically polarized light

Abstract: The generalization to circularly polarized modes of the Kramers-Kronig relations for the complex refractive index is discussed in terms of the analyticity of the index to clarify the physical basis of the generalized dispersion relations. A compact form for the circular-mode dispersion relations is obtained that is particularly useful in treating dichroic effects and for deriving optical sum rules. The procedure is generalized to elliptically polarized modes. It is shown that the generalized dispersion relations must be used for the optical constants of elliptic modes that retain their ellipticity to arbitrarily small frequencies, while dispersion relations of the Kramers-Kronig form apply to elliptic modes that are linearly polarized in the limit of small frequencies.

Linear Polarimeter with rapid modulation, achromatic in the 0.3-1.1-microm range.

Abstract: A polarimeter is described, which provides achromatic modulation over the spectral range 0.3 to 1.1 microns, with very small light losses. The instrument is the first one to use superachromatic half-wave plates; such a plate is made of three achromatic half-wave plates of quartz and magnesium fluoride cemented with the optical axis of the central plate making an angle of 1.00 rad with the axes of the parallel-oriented outer half-wave plates. Wavelength dependence of the axis direction of the optical axis was eliminated by using two identical such plates in front of a Wollaston prism. The plate closer to the prism is stationary, while the other is continuously rotated by a stepper motor. In the polarimeter constructed, the range of instrumentally induced wavelength dependence of the plane of polarization did not exceed 0.002 rad. Using the polarimeter on a 228-cm telescope, a 10-min integration through the blue filter of the UBV photometric system for a star of magnitude 10.0 gives the percentage polarization with a mean error of + or - 0.014%.

The origin of optical polarization in NGC 1068

Abstract: The polarization of emission lines in the nucleus of NGC 1068 has been measured with a digicon, a single-channel scanner, and interference filters. It is found that the permitted lines of H and probably also He II are polarized at nearly the same position angle and by the same amount as the neighboring continuum. This argues strongly that a common dust scattering mechanism is responsible for all the polarization. The forbidden lines are weakly polarized at a position angle quite different from the continuum, indicating an origin outside the nuclear scattering region. The continuum radiation has been found to be circularly polarized with ellipticity of the order of 5 percent in the red. Such high ellipticity is very unlikely to be of nonthermal origin. We take it as evidence that the nuclear dust is in the form of clouds in an asymmetric skew geometry; the polarization then arises from multiple scattering within these clouds.

Transmission characteristics of a twisted nematic liquid-crystal layer*

Abstract: An approximate analytical expression is calculated for the transmission of thin twisted nematic layers situated between a polarizer/analyzer pair. The approximation assumes that the twist angle of the nematic liquid crystal is smaller than the maximum retardation of the cell. The direction of the incident light is assumed to be parallel to the normal of the electrode. This configuration is analyzed for a general arrangement of polarizer and analyzer; the general result is evaluated for the case of the polarizer parallel and analyzer perpendicular to the liquid-crystal optical axis on the input and output electrodes, respectively. The results show that in the case of a thin twisted nematic layer the transmission depends on the thickness of the layer, on the birefringence of the liquid crystal, and on the wavelength of the light. This is a departure from the well-known independence of the transmission on these parameters for a thick twisted nematic layer.

Molecular theory of optical polarization and light scattering in dielectric fluids. I. Formal theory

Abstract: A molecular theory, based on first principles, is introduced for the systematic study of the eA'ects of intermolecular forces on optical properties of dielectric molecular fluids This theory covers a broad range of applications, including (polarized and depolarized) Rayleigh and Raman scattering, absorption spectra, and nonlinear optics A canonical transformation is presented by which externally applied coherent fields can be separated from internal radiation fields, thus enabling the introduction of radiative corrections (such as retardation) to the intermolecular forces The polarization of the medium is expressed in terms of a manybody polarizability (or nonlocal susceptibility) operator The latter quantity contains implicitly all so-called local-field effects (modification of the molecular polarizability by electromagnetic fields due to neighboring molecules) The dipolar contributions, when summed to all orders, yield the familiar Lorentz-Kirkmood factor, involving the retarded dipole tensor

Proof of the Resonant Acceleration Mechanism for Fast Electrons in Gaseous Laser Targets

Abstract: We report the observation of fast-electron emission (10-20 keV) from gaseous targets irradiated by a C${\mathrm{O}}_{2}$ laser pulse. The electrons are emitted in a direction 30\ifmmode^\circ\else\textdegree\fi{} away from the electric vector, but in the plane of optical polarization. This is the first direct experimental observation of the resonant absorption effect, which has been proposed as being responsible for the efficiennt laser energy deposition in a plasma. In contrast, the parametric decay instability is not consistent with the observations.

Principles of Dye Laser Operation and Dye Laser Tuning Methods

Abstract: Organic dye lasers have proved to be a high-intensity source of monochromatic radiation that can be tuned to any desired wavelength in the visible range of the spectrum In this contribution the basic principles of dye laser operation are treated within the model of a suitably modified four-level laser, described in the rate equation approach The tuning methods based on dispersion by prisms, diffraction by gratings, interferometric effects and polarization effects are discussed In addition, examples of dye lasers, which are rapidly tunable or which emit simultaneously two or more wavelengths, and some interesting properties of ring lasers are presented

Electrooptic guided-to-unguided mode converter

Abstract: Experimental demonstration of electrooptic polarization conversion from a guided TE wave to an unguided TM wave in a thin-film light guide is reported. In the specific device we fabricated utilizing Ta 2 O 5 film and LiTaO 3 substrate, we have observed a 40-percent modulation when 500 V were applied across two electrodes spaced 50 μm apart. We present here a ray-optics analysis of the conversion process. With the inclusion of the Goos-Haenchen shifts, the analysis agrees well with the experiment.

Multiple scattered radiation emerging from Rayleigh and continental haze layers. 2: Ellipticity and direction of polarization.

Abstract: The ellipticity and the direction of polarization are calculated for radiation that has undergone multiple scattering from plane parallel layers. Both the radiation emerging from the top of the layer and that transmitted through the bottom are considered. Two different phase functions are used for the scattering layer: Rayleigh and haze L. The direction of polarization of the reflected radiation shows little variation as the optical depth of the layer increases, while there is a much larger variation for the transmitted radiation. When the optical thickness is small, the direction of polarization for haze L varies rapidly with zenith angle near those angles at which the single scattered polarization is zero. The ellipticity of the radiation from haze L layers increases at first in direct proportion to the optical thickness of the layer. In general the ellipticity of the transmitted radiation is considerably greater than that of the reflected because of the greater average number of photon collisions in the frmer case. When the ellipticity is small, it is shown that the product of the polarization and the ellipticity is closely equal to -V/2I, where I and V are the first and fourth components of the Stokes vector.

Optical polarization models of quasi-stellar objects and BL Lacertae objects

Abstract: A model for optically thin synchrotron radiation from a region of partially aligned magnetic field is compared with optical linear polarization data for QSOs and BL Lacertae objects. The synchrotron theory is treated by considering the magnitude and angle of the field perpendicular to the line of sight to be described by a probability distribution. A quite general argument shows that on such a model the linear polarization should depend much more steeply on the spectral index of the radiation than it does in the case of a perfectly aligned field. For two general classes of field asymmetry, the polarization usually depends linearly or quadratically on the spectral index and on the square of the field alignment, for small values of the alignment. QSO data from the literature together with new observations of BL Lacertae objects are gathered together and compared with this model; a 15--20 percent upper limit for the field alignment is consistent with the polarization of the nonvariable objects and the quiescent polarization of the variables, while the highly polarized bursts of the variables require less than a factor of 2 enhancement in the alignment. For objects with curved spectra, perhaps due to upper energy cutoffs inmore » the electron spectrum, the theory predicts a polarization which rises gradually with frequency. This polarization wavelength dependence is weak over the optical band, but should be easily observable in those BL Lacertae objects with curved spectra, once polarization observations have been extended beyond the optical window. A possible observation of this effect in PKS 0735+17 in the optical on three nights is presented. (AIP)« less

A polarization survey of stars near the Orion nebula.

Abstract: The amounts and origins of polarization are considered as a function of stellar spectral type and color. (AIP)

Polarization reversal in the tail of comet Ikeya-Seki (1965 VIII).

Abstract: Multicolor observations of brightness and polarization in the continuum throughout the tail of Comet 1965 VIII reveal the presence of positive and negative polarization (polarization reversal) characteristic of slightly absorbing particles. The phase angle of the neutral point is found to vary with color and with time, the latter indicating short-term changes in the properties of the particles after perihelion.

Raman spectrum and refractive index behavior of Al2O3 added high‐silica‐content glass

Abstract: Several specimens of Al2O3‐added high‐silica‐content glass of various additive concentration which were prepared with a chemical vapor deposition (CVD) process are studied by Raman spectroscopy. The Raman spectrum of the glass is found to be close to that of fused silica, and the Raman band characteristic to the nonbridging oxygens was not observed in this glass. A quadratic behavior of the refractive index change as a function of the additive concentration is observed in this glass and is explained with a detailed ionic polarizability concept on the basis of the Raman spectroscopy. The effect of the refractive index fluctuation in this glass on the optical attenuation is also discussed.