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Showing papers on "Optical polarization published in 1996"


Journal ArticleDOI
TL;DR: In this paper, the design and construction of two different types of multiple-beam optical tweezers, each equipped with nanometer-resolution position detectors, are described and compared, including designs that are relatively insensitive to absolute location of a trapped particle within the field of view.
Abstract: We describe the design and construction of two different types of multiple-beam optical tweezers, each equipped with nanometer-resolution position detectors. Multiple optical traps can be created either by splitting a laser beam in two parts, based on its polarization, or time-sharing a single beam among several different locations. The advantages and disadvantages of optical tweezers based on either scheme are discussed, along with details of specific implementations. Various ways to detect microscopic movements of an optically trapped object are presented and compared, including designs that are relatively insensitive to absolute location of a trapped particle within the field of view. Two of many possible applications for such instruments are illustrated: the detection of molecular steps by kinesin motor molecules, and determinations of the stiffness of single microtubules.

486 citations


Journal ArticleDOI
29 Nov 1996-Science
TL;DR: Analytical analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole, and that observations of periodically solar-illuminated lunar surfaces, including the north pole, yielded no enhancement.
Abstract: During the Clementine 1 mission, a bistatic radar experiment measured the magnitude and polarization of the radar echo versus bistatic angle, beta, for selected lunar areas. Observations of the lunar south pole yield a same-sense polarization enhancement around beta = 0. Analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole. Radar observations of periodically solar-illuminated lunar surfaces, including the north pole, yielded no such enhancement. A probable explanation for these differences is the presence of low-loss volume scatterers, such as water ice, in the permanently shadowed region at the south pole.

425 citations


Journal ArticleDOI
TL;DR: The temporal profiles of polarized laser pulses propagating through a scattering medium differ for scattered light parallel and perpendicular to the incident polarization, which can be used as a time gate for the early portion of the scattered light, reducing the diffusive component.
Abstract: The temporal profiles of polarized laser pulses propagating through a scattering medium differ for scattered light parallel and perpendicular to the incident polarization. The degree of polarization is conserved over 100 ps after the arrival of the ballistic component. This observation can be used as a time gate for the early portion of the scattered light, reducing the diffusive component.

159 citations


Journal ArticleDOI
TL;DR: Arguments are presented that suggest different scattering mechanisms for the two polarizations: evenly distributed Bragg scatter patches for VV and scatter from small asymmetric bore features for HH, while HH NRCS grazing angle characteristics are shown to correlate with biological activity indicators of the coastal waters.
Abstract: Reports on experiments featuring horizontally (HH) and vertically (VV) polarized X-band marine radar sea scatter imagery in the coastal environments of Bermuda and La Jolla, under light to moderate winds and the absence of long gravity waves. These conditions allowed the study of fundamental scattering mechanisms from small scale roughness and short waves of a few meters wavelength or less, shorter than the radar pulse. While a large fraction of radar data collected revealed the presence of slick bands, the authors analyze the radar echo of ambient background outside of the slicks. Sea scatter data were digitally recorded for 360/spl deg/ azimuthal coverage for grazing angles between 1-3.5/spl deg/, and were converted to normalized radar cross section (NRCS or /spl sigma//spl deg/) images. The HH and VV polarizations show quite different spatial texture, with HH exhibiting a discrete character and VV being more nearly spatially homogeneous. Grazing angle dependencies are different for HH and VV: upwind-downwind differences of mean NRCS show ratios of just 4-6 dB for VV, but are equal or greater than the 16-dB noise-imposed limit for HH for the low wind conditions. HH NRCS grazing angle characteristics are shown to correlate with biological activity indicators of the coastal waters, with a fourth power dependence in relatively unproductive waters, to a nearly quadratic in productive waters. Arguments are presented that suggest different scattering mechanisms for the two polarizations: evenly distributed Bragg scatter patches for VV and scatter from small asymmetric bore features for HH. A multipath illumination model for small bore features is outlined, and scale sizes for the small scale breakers inferred from the experimental results presented are between 2 and 4 cm in height, with crest widths between 24 and 48 cm.

98 citations


Journal ArticleDOI
TL;DR: In this paper, a quantum well infrared photodetector geometry for normal incidence light coupling was reported, which utilizes total internal reflection at the sidewalls of triangular wires to create favorable optical polarization for infrared absorption.
Abstract: In this letter, we report a quantum well infrared photodetector geometry for normal incidence light coupling. The new optical coupling scheme utilizes total internal reflection at the sidewalls of triangular wires to create favorable optical polarization for infrared absorption. These wires are created by chemically etching an array of V grooves through the detector active region along a specific crystallographic direction. Experimental results from the initial single color as well as two‐color detectors with linear wires and unthinned substrate show efficient light coupling comparable to the standard 45° edge coupling, without the undesirable wavelength dependence or spectral narrowing effect of a conventional grating structure. At the same time, the dark current density is substantially reduced due to the partial material removal. Further improvement is expected by creating a two‐dimensional coupling structure with substrate thinning.

84 citations


Journal ArticleDOI
TL;DR: In this paper, the uniaxial strain effect on the GaN-based laser was investigated on the basis of k⋅p theory and it was found that neither compressive nor tensile biaxia strains in the c plane are so effective on the reduction of the threshold carrier density as conventional zinc-blende lasers.
Abstract: In order to clarify the strain effect on the GaN‐based lasers and to give the important guideline on their device design, the subband structure and the optical gains of strained wurtzite GaN/AlGaN quantum wells are theoretically investigated on the basis of k⋅p theory. First‐principles band calculations are used for deriving the unknown physical parameters. It is found that neither compressive nor tensile biaxial strains in the c plane are so effective on the reduction of the threshold carrier density as conventional zinc‐blende lasers and that the uniaxial strain in the c plane is very useful for reducing it. The relation between the uniaxial strain’s direction and the optical polarization is also clarified. As a result, we suggest that the uniaxial strain in the c plane is one of the preferable approaches for the efficient improvement of the GaN‐based lasers performance.

81 citations


Journal ArticleDOI
P.F. Wysocki1, V. Mazurczyk2
TL;DR: In this article, a computer model for polarization dependent gain in Er-doped fiber amplifiers (EDFA) is presented, which assumes that each erbium ion possesses an ellipsoidal gain surface and that all ion orientations are equally likely.
Abstract: A computer model for polarization dependent gain (PDG) in Er-doped fiber amplifiers (EDFA) is presented. The model assumes that each erbium ion possesses an ellipsoidal gain surface and that all ion orientations are equally likely. By dividing the ions into subsets based upon orientation and computing the inversion of each subset in the presence of polarized pump and signal waves, the model predicts the dependence of the PDG induced by this polarization hole-burning (PHB) on the design of the EDFA, the signal degree and state of polarization (SOP), and the pump SOP. For moderate gain amplifiers (made from the same fiber) with the same gain peak wavelength and the same compression level, the magnitude of the PDG is nearly independent of the EDFA gain. Internal and random fiber birefringence are included to model real fibers. In fibers which cause the signal SOP to walk rapidly around the Poincare sphere, the PDG is reduced by a factor of 2/3 when compared with a linear polarization-maintained signal. Scrambled signals and partially-polarized saturating tones are also considered. Simple rules are derived for predicting the PDG of a given EDFA.

77 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of nonequilibrium solvation on the molecular properties of a solvated compound are investigated using high-frequency electromagnetic fields, where the optical polarization vector is at all times assumed to be in equilibrium with the charge distribution of the solute.
Abstract: We present an extension of the molecular response method of solvated compounds. The extension treats in a proper fashion the effects of nonequilibrium solvation on the molecular properties of the solvated compound. The molecular properties evaluated within the response formalism are properties that are measured using high-frequency electromagnetic fields. We consider the changes in the molecular properties due to nonequilibrium solvation. The nonequilibrium solvation arises from changes in the molecular charge distribution induced by the high-frequency perturbation. The optical polarization vector is at all times assumed to be in equilibrium with the charge distribution of the solute, contrary to the inertial polarization, which is not necessarily in equilibrium with the charge distribution of the solute. We calculate shifts of excitation energies and frequency-dependent polarizabilities as a function of the optical and static dielectric constants.

71 citations


Patent
TL;DR: In this paper, the authors proposed a novel, rapidly tunable and wide instantaneous bandwidth (e.g., 1 Khz-100 Mhz) ultrasonic probe system for therapy, diagnostics, and non-invasive surgery, particularly for intracavity operation with a typical 100 channel/transducer element count.
Abstract: Wavelength diversity coupled with fiber-based time delay, optical energy delivery, and ultrasonic energy sensing, are proposed to form a novel, rapidly tunable (e.g., 1 Khz-100 Mhz) and wide instantaneous bandwidth (e.g., >50% bandwidth at center carrier), ultrasonic probe system for therapy, diagnostics, and non-invasive surgery, particularly for intracavity operation with a typical 100 channel/transducer element count. This ultrasonic system architecture is a multi-wavelength optical delay line module using two high speed (i.e., <10 microseconds wavelength switching time), bulk acousto-optic tunable filters, that provide collinear, high power, multi-wavelength optical input and output beams. This wavelength selection module also provides high optical throughput (e.g., 90% efficiency) and excellent (e.g., -30 db) optical blockage of the unwanted leakage (undiffracted) light, preventing noise propagation when such modules are cascaded to provide many variable signal time delays. The overall system also uses another multi-wavelength module that adjusts the optical polarization of the optical beams at various critical stages of the proposed polarization sensitive ultrasonic control system. This polarization controller is based on an interferometric design using a variety of low loss two dimensional pixelated thin-film device arrays of various types of liquid crystals such as twisted nematic, parallel-rub birefringent-mode, and ferroelectric. These liquid crystal devices form the required polarization mode converters, phase shifters and half-wave plates required to form our novel polarization control module.

61 citations


Journal ArticleDOI
F. Heismann1
TL;DR: In this article, the operation and implementation of compact electro-optic polarization scrambler on x-cut and z-cut lithium niobate is described, and simple linear phase retarders that depolarize light in a fixed, well-maintained polarization state as well as cascaded multi-stage scrambler that are capable of depolarizing arbitrarily polarized light.
Abstract: Fast polarization scramblers have become important components in optically amplified transoceanic communication systems to eliminate anisotropic gain saturation (polarization hole burning) in the erbium-doped fiber amplifiers by depolarizing the launched optical carrier. This paper reviews the operation and implementation of compact electro-optic polarization scramblers on x-cut and z-cut lithium niobate. These integrated-optic devices employ low-loss single-mode waveguides and allow polarization modulation at variable frequencies ranging from a few 100 Hz to more than 10 GHz. We describe simple linear phase retarders that depolarize light in a fixed, well-maintained polarization state as well as cascaded multi-stage scramblers that are capable of depolarizing arbitrarily polarized light. These scramblers can be operated over a broad optical bandwidth of more than 40 nm with less than 5% residual degree of polarization and are further wavelength-tunable over more than 100 nm.

54 citations


Journal ArticleDOI
TL;DR: In this article, a measurement procedure was developed and tested to determine horizontal and vertical polarization radiative transfer properties, i.e., single scattering albedo and optical depth, of vegetation under field conditions.
Abstract: A measurement procedure has been developed and tested to determine horizontal and vertical polarization radiative transfer properties, i,e., single scattering albedo (/spl omega/) and optical depth (/spl tau/), of vegetation under field conditions. The procedure was applied to a wheat crop for a series of biomass densities. The measurements were done using two different radiometers (1.4 and 5 GHz) and for different view angles. The measurements and calculations indicated that the ratios of horizontal and vertical polarization radiative transfer properties (/spl alpha/=/spl Gamma//sub h///spl Gamma//sub /spl nu//, /spl alpha/'=/spl tau//sub h///spl tau//sub /spl nu// and /spl beta/=/spl omega/h//spl omega//sub /spl nu//) are slightly dependent on view angle. However, no significant dependence on biomass density could be discerned.

Journal ArticleDOI
TL;DR: In this article, a detailed study of the polarization properties of a reflective fiber amplifier composed of a circulator, a normal single-mode Er-doped fiber and a Faraday rotator mirror is presented.
Abstract: We present a detailed study of the polarization properties of a reflective fiber amplifier composed of a circulator, a normal single-mode Er-doped fiber and a Faraday rotator mirror. The amplifier can preserve an arbitrary input state of polarization regardless of any external perturbations, and is completely free from polarization effects. The effect of imperfections of the Faraday rotator mirror is also discussed. Finally, we demonstrate experimentally the polarization-stability of the amplifier and its ability to compensate polarization mode dispersion both in the circulator and in the single-mode Er-doped fiber.

Journal ArticleDOI
TL;DR: In this article, a unified finite element beam propagation method is described for both TE and TM waves propagating in strongly guiding and longitudinally varying optical waveguides with magnetooptic materials.
Abstract: A unified finite element beam propagation method is described for both TE and TM waves propagating in strongly guiding and longitudinally varying optical waveguides with magnetooptic materials. In order to avoid nonphysical reflections from the computational window edges, the transparent boundary condition is introduced for both polarizations. In order to show the validity and usefulness of this approach, numerical examples are presented for a directional coupler composed of two parallel identical waveguides, an S-bend, a Y-branching optical isolator, and a 4-ports optical circulator. The present algorithm is, to our knowledge, the first beam propagation method for modeling nonreciprocal magnetooptic components.

Journal ArticleDOI
TL;DR: The temporal profiles of the degree of polarization of the output light depends on the wavelength of the light and the type of the tissue that it propagates as mentioned in this paper, which is the same as the temporal profile of the polarization information of light propagating through the tissue.

Journal ArticleDOI
TL;DR: In this article, the uniaxial strain effect in the (0001) plane on the electronic and optical gain properties of wurtzite GaN/AlGaN quantum well lasers is investigated on the basis of kp theory.
Abstract: The uniaxial strain effect in the (0001) plane on the electronic and optical gain properties of wurtzite GaN/AlGaN quantum well lasers is investigated on the basis of kp theory. In order to obtain the required physical parameters, the first-principles band calculations are used. It is found that the uniaxial strain in the (0001) plane causes much lower threshold current density than the biaxial strain does. The relation between the uniaxial strain's direction and the optical polarization is clarified as well. As a result, we predict that the uniaxial strain in the (0001) plane is one of the preferable approaches for the efficient improvement of the GaN-based lasers performance.

Journal ArticleDOI
TL;DR: In this paper, a theoretical and experimental analysis of thermal stress effects on the modal polarization properties of highly elliptical-core fibers is presented, based on solving the vectorial Maxwell's equations, using a finite-element scheme.
Abstract: A theoretical and experimental analysis of thermal stress effects on the modal polarization properties of highly elliptical-core fibers is presented. The theoretical analysis is based on solving the vectorial Maxwell's equations, using a finite-element scheme, when form-induced and stress-induced effects are introduced simultaneously through appropriate calculation of the refractive indexes of the anisotropic media. The experimental analysis is done by studying the temperature response of a white-light interferometric sensor employing highly elliptical-core fibers. The calculated temperature sensitivities of the modal birefringence and the polarization mode dispersion in highly elliptical-core fiber are in close agreement with the experimental results. Interpretation of the results useful for designing white-light interferometric sensors composed of highly elliptical-core fibers is also given.

Journal ArticleDOI
TL;DR: In this paper, power leakage properties and guiding conditions of rib antiresonant reflecting optical waveguides (rib-ARROW) have been theoretically and experimentally studied as a function of wavelength and polarization of the light for different geometrical and optical parameters that characterize the rib-arrOW structure.
Abstract: Power leakage properties and guiding conditions of rib antiresonant reflecting optical waveguides (rib-ARROW) have been theoretically and experimentally studied as a function of wavelength and polarization of the light for different geometrical and optical parameters that characterize the rib-ARROW structure. Obtained results show that rib-ARROWs can only be fabricated with low losses in a wavelength range when determined rib configurations are adopted. Furthermore, these waveguides exhibit a polarization sensitivity that largely depends on the core-substrate refractive index difference. Together with the experimental results, theoretical calculations from different modeling methods are also presented and discussed.


Journal ArticleDOI
TL;DR: In this article, a femtosecond four-wave mixing technique was used to measure the ultrafast coherent dynamics of the optical polarization in semiconductor optical amplifiers, and the dephasing time close to the transparency point is on the order of 100 fs.
Abstract: A femtosecond four‐wave mixing technique is used to measure the ultrafast coherent dynamics of the optical polarization in semiconductor optical amplifiers. A heterodyne detection scheme enables us to measure a background‐free quasi‐degenerate four‐wave mixing signal even without spatial separation of the pump and probe beam. First results indicate that the polarization dephasing time close to the transparency point is on the order of 100 fs.

Journal ArticleDOI
24 Jan 1996-Langmuir
TL;DR: Birefringence, arising from locally preferred orientation of molecules or functional groups in polymeric and related materials has been observed in a near-field scanning optical microscope (NSOM).
Abstract: Birefringence, arising from locally preferred orientation of molecules or functional groups in polymeric and related materials has been observed in a near-field scanning optical microscope (NSOM) a...

Journal ArticleDOI
17 Jun 1996
TL;DR: In this paper, a new refractometer with a variable length vacuum cell was developed to eliminate errors caused by deformations in optical windows of the cell, and a combined standard uncertainty of 5/spl times/10/sup -9/ in the measurement of the refractive index of air was achieved.
Abstract: A new refractometer with a variable length vacuum cell has been developed to eliminate errors caused by deformations in optical windows of the cell. The refractive index of air is determined by measuring the changes in the optical path difference between the air of interest and a vacuum as a function of the changes in the cell length. An optical phase modulation technique and a dark fringe detection method are used to obtain a high resolution in measuring the optical path difference by a double-pass Michelson interferometer. A combined standard uncertainty of 5/spl times/10/sup -9/ in the measurement of the refractive index of air has been achieved.

Journal ArticleDOI
TL;DR: Fully packaged, polarization independent, integrated acoustooptic 2/spl times/2 switches have been developed which can be also used as add/drop multiplexers as discussed by the authors.
Abstract: Fully packaged, polarization independent, integrated acoustooptic 2/spl times/2 switches have been developed which can be also used as add/drop multiplexers. The devices have been fabricated in X-cut Y-propagating LiNbO/sub 3/ and can be operated at wavelengths around 1550 nm. They consist of passive polarization splitters and acoustooptic TE-TM converters with weighted coupling. A filter bandwidth of 2.0 nm and a tuning range of 130 nm have been obtained. The fiber-to-fiber insertion loss is <4.6 dB and a residual polarization dependence of 1.3 dB for bar-state and 0.1 dB for cross-state routing has been achieved.

Journal ArticleDOI
TL;DR: It was noticed that at moderate angles of incidence, the scattering profile as a function of observation angle is fairly independent of the incident polarization and operating frequency, which justifies the use of the geometric optics approximation embodied in the Kirchhoff formulation for surfaces with large surface radius of curvature.
Abstract: Despite the recent development of analytical and numerical techniques for problems of scattering from two-dimensional rough surfaces, very few experimental studies were available for verification. The authors present the results of millimeter-wave experiments on scattering from two-dimensional conducting random rough surfaces with Gaussian surface roughness statistics. Machine-fabricated rough surfaces with controlled roughness statistics were examined. Special attention was paid to surfaces with large rms slopes (ranging from 0.35 to 1.00) for which enhanced backscattering is expected to take place. Experimentally, such enhancement was indeed observed in both the copolarized and cross-polarized returns. In addition, it was noticed that at moderate angles of incidence, the scattering profile as a function of observation angle is fairly independent of the incident polarization and operating frequency. This independence justifies the use of the geometric optics approximation embodied in the Kirchhoff formulation for surfaces with large surface radius of curvature. When compared with the experimental data, this analytical technique demonstrates good agreement with the experimental data.

Proceedings ArticleDOI
18 Jun 1996
TL;DR: A robust and accurate polarization phase-based technique for material classification is presented, based on the physical principle that metals retard orthogonal components of light upon reflection while dielectrics do not, and can be easily implemented with existing imaging technology.
Abstract: A robust and accurate polarization phase-based technique for material classification is presented. The novelty of this technique is three-fold In (i) its theoretical development, (ii) its application, and, (iii) its experimental implementation. The concept of phase of polarization of a light wave is introduced to computer vision for discrimination between materials according to their intrinsic electrical conductivity, such as distinguishing conducting metals, and poorly-conducting dielectrics. Previous work has used intensity, color and polarization component ratios. This new method is based on the physical principle that metals retard orthogonal components of light upon reflection while dielectrics do not. This method has significant complementary advantages with respect to existing techniques, is computationally efficient, and can be easily implemented with existing imaging technology. Experiments for real circuit board inspection, non-conductive and conductive glass, and, outdoor object recognition have been performed to demonstrate its accuracy and potential capabilities.

Journal ArticleDOI
TL;DR: Optimum polarization states are derived and the results are discussed in relation to the classic radar optimum polarizations.
Abstract: Specular null polarization theory (SNPT) has been recently introduced for the case of coherent scattering where a 2/spl times/2 scattering matrix is sufficient to describe the scattering process. In this paper, SNPT is extended to the case of incoherent scattering. Optimum polarization states are derived and the results are discussed in relation to the classic radar optimum polarizations. In traditional radar polarimetry, modeling of the radar receive/transmit network is included in the radar voltage equation and consequently this affects the optimum polarizations and polarization responses of scatterers. SNPT eliminates this effect and therefore allows for a more direct analysis of scatterers. Modeling of ensembles of precipitation particles is used to illustrate the results of the analysis.

Journal ArticleDOI
J.-P. Weber1, B. Stoltz, H. Sano, M. Dasler, O. Oberg, J. Waltz 
TL;DR: In this paper, the multigrating filter (MGF), a tunable channel selection filter for wavelength division multiplexed (WDM) transmission systems, has been presented.
Abstract: After a review of the design principles, we present new experimental and theoretical results about the multigrating filter (MGF), a tunable channel selection filter for wavelength division multiplexed (WDM) transmission systems. Bit error rates mere measured at 2.5 Gb/s for single- and multichannel operation of a packaged polarization independent four-channel MGF with integrated amplifiers. The single-channel results are compared with theory. A monolithic tunable channel dropping component has also been fabricated by integrating two MGF's, a splitter, and amplifiers. Bit error rates measurements are presented for optical (at 2.5 Gb/s) and electrical on-chip (at 622 Mb/s) channel dropping in single- and multichannel operation.

Journal ArticleDOI
TL;DR: In this article, the authors considered polarization-squeezed (PS) light generation in anisotropic Kerr medium and showed the possibility to transform PS light into light with sub-Poissonian statistics by linear conversion (phase plate and analyser).
Abstract: We consider polarization-squeezed (PS) light generation in anisotropic Kerr medium. The fluctuations of the Stokes parameter either S 2 or S 3 are suppressed in PS light. We show the possibility to transform PS light into light with sub-Poissonian statistics by linear conversion (phase plate and analyser). The quantum properties of the second harmonic (SH) generated by frequency doubling of the PS light are investigated.

Journal ArticleDOI
TL;DR: In this article, a polarization independent and contrast-ratio-enhancing all-optical wavelength shifting module using polarization-dependent SOA's is presented. But the performance of this module is limited to upshifting over 19 nm at 1 Gb/s.
Abstract: We demonstrate a polarization-independent and contrast-ratio-enhancing all-optical wavelength shifting module using polarization-dependent SOA's. When comparing our robust module to a single polarization-dependent SOA wavelength shifter, we reduce the polarization dependence from 3.5-0.5 dB and the contrast-ratio-induced power penalty from 5-1.5 dB when upshifting over 19 nm at 1 Gb/s.

Journal ArticleDOI
TL;DR: In this article, the authors present results of optical linear polarization measurements of stars in the region of the relatively isolated cometary globule CG 12 in Centaurus at a galactic latitude b ≃ 21°.
Abstract: We present results of optical linear polarization measurements of stars in the region of the relatively isolated cometary globule CG 12 in Centaurus at a galactic latitude b ≃ 21°. A polarization map representing the geometry of the magnetic field in the cloud is produced. In the lower-density outer parts of the cloud, the field is more or less parallel to the cometary tail and other elongated structures like the bipolar molecular outflow from near the infrared source IRAS 13547-3944 and the nebulosity around star 2 embedded in the cloud. Polaization vectors for the more highly reddened stars in the head region of the globule are found to be more or less parallel to the long axis of the elliptical, high-density C 18 O core of the cometary globule head.

Journal ArticleDOI
TL;DR: In this article, optical and X-ray observations of the AM Her system RE J1844 - 74 using the Anglo-Australian Telescope (AAT) and ROSAT were used to derive a new accurate ephemeris for the spin period of the white dwarf.
Abstract: We report optical and X-ray observations of the AM Her system RE J1844 - 74 using the Anglo-Australian Telescope (AAT) and ROSAT From previously published data and these new data we derive a new accurate ephemeris for the spin period of the white dwarf We find we cannot simultaneously fit the green and red polarization data However, we can fit them separately using different values of the plasma parameter, Lambda We investigate the possible reasons for this result Furthermore, we find that the polarization data require long narrow accretion arcs This is in contrast to results on eclipsing AM Her systems which tend to favour accretion regions that are relatively small, We briefly explore the possible effects that may influence the determination of the size of the accretion region from these different methods We find evidence that the main accretion region of RE J1844 - 74 has a magnetic field strength similar to 10 MG less than its secondary pole, and that the system inclination is moderately high, Our X-ray data are out of phase with the optical data, consistent with our current view of the accretion flow in AM Her systems