Showing papers on "Optical polarization published in 1978"

cw three-wave mixing in single-mode optical fibers

Abstract: Strong continuous three‐wave mixing of 514.5‐nm argon laser light in a single‐mode fiber is reported. The effect, due to the third‐order nonlinearity of silica, has been observed for light whose frequency spectrum consists of either a few discrete monochromatic frequency components separated by ∼1 GHz or a quasicontinuous distribution of frequencies having a spectral envelope ∼4 GHz wide. We show that the effect provides a simple and effective method for measuring the nonlinearity of silica. In the first manifestation of the effect, the nonlinearity mixes the frequency components to produce new frequencies. In the second, multiple mixing occurs that broadens the quasicontinuous spectrum. This manifestation of the effect is large; broadening by a factor of 4 has been observed with lower intensity levels than are required to produce stimulated Brillouin scattering in the same fiber. A theoretical model is presented to describe spectral broadening by three‐wave mixing for the case of small broadening. The effect of three‐wave mixing on the operation of continuous stimulated Brillouin and Raman oscillators is also discussed. Finally, it is noted that the presence of this effect may constrain the design of long‐haul single‐mode fiber optical communication trunks.

Linear polarization in birefringent single‐mode fibers

Abstract: Single‐mode fibers which maintain linear polarization are described. The fibers are birefringent and linear polarization is maintained along either of the two principal axes. The birefringence arises from the deliberate enhancement of anisotropic strains.

Diagrammatic analysis of the density operator for nonlinear optical calculations Pulsed and CW responses

Abstract: In the present paper a diagrammatic analysis of the density operator for the evaluation of nonlinear optical quantities is considered. The present approach extends earlier diagrammatic analysis by treating the time evolution of both the wave function and its complex conjugate. Time-ordered graphs result, each of which corresponds to a term in the density matrix. Examples involving the third-order susceptibility are discussed for both monochromatic and pulse excitation. In particular coherent rotational transient birefringence is discussed. The diagrams provide a convenient means by which nonlinear optical processes can be precisely defined and the susceptibility readily evaluated.

Coherent Raman gain spectroscopy using CW laser sources

Abstract: The recent demonstration of stimulated Raman gain (loss) spectroscopy (SRS) using CW laser sources introduces a powerful tool to coherent Raman spectroscopy. In this paper we undertake an experimental and analytical evaluation of several variations of SRS using CW laser sources including (1) direct stimulated Raman gain (loss) measurements, (2) optically heterodyned polarization interferometry, and (3) two-beam nonlinear interferometry. The results show CW SRS to be a convenient and effective means of obtaining direct Raman spectra in applications where background fluorescence precludes the use of conventional Raman techniques. Sensitivities comparable to or exceeding those obtained by coherent anti-Stokes Raman spectroscopy (CARS) are demonstrated. Ultimate sensitivities exceeding those achieved by spontaneous Raman spectroscopy are expected for high-resolution applications in gaseous media.

Polarization characteristics of noncircular core single-mode fibers

Abstract: It is well known that geometrical or dielectric imperfections in conventional graded-index single-mode fibers depolarize light after a few centimeters. A slight improvement in the polarization performance of these fibers is achieved by introducing noncircularity in the core shape. This is evident from the measurements on borosilicate fibers with dumbbell shaped cores. This result is correlated with Marcatili’s analysis, which shows that changing the core geometry, from square to rectangular, does not appreciably alter the difference in the propagation constants of the two fundamental modes with orthogonal polarizations. Thus, the noncircular geometry and the associated increase in stress-induced birefringence introduced during the manufacturing process alone are not sufficient to improve the polarization performance, and the enhancement of the anisotropic birefringence is necessary to achieve single-polarization fibers.

Emission continua of rare gas plasmas

Abstract: Photoionization cross sections of rare gases have been calculated by using the scaled Thomas-Fermi method, including polarization effects. Absorption coefficients have been derived for bound-free transitions in thermal plasmas of 6000 K to 30000 K, for a wavelength range from 300 A to 10000 A.

Stellar polarization and the structure of the magnetic field of our galaxy

Abstract: The stellar polarization data have been examined using a new catalogue containing accurate stellar distances. On the assumption of a magnetic alignment hypothesis, correlations on the larger distance scale indicate the existence of a dominant regular magnetic field, although its characteristics are difficult to determine. Within 500 pc its direction is towardsl≈45° and beyond this towardsl≈60°, though it is clear that such a longitudinal model is too simple. There is also some evidence for an inclination of this field to the galactic plane. The distribution of the polarization vectors away from the galactic plane has been examined and it is proposed that the two largest loop structures, previously identified as Supernova remnants, are linked by the regular field. Incremental polarization maps have been produced but they show little correlation with the spiral structure. The polarization appears to be saturated at about 1 kpc from the Sun, which is explained as the result of an observational selection effect. On the smaller distance scales an autocorrelation analysis in different directions has revealed no obvious coherence in the irregular component on scales greater than 50 pc.

Incoherent backscatter from rough surfaces: The two‐scale model reexamined

Abstract: An expression for the incoherent backscatter cross section per unit area of a two-scale rough surface is derived that includes the effects of local polarization tilt angles, thus providing a first-order cross-polarized scattering component. A rigorous numerical method of evaluating the derived expression is developed and two approximate solutions are also derived. The approximate solutions clarify the two-scale interaction for the cases of diffuse and quasi-specular small-scale scattering. Calculated scattering distributions are compared with experimental data at radar and optical frequencies using both perturbation theory and physical optics polarization coefficients. Good agreement with copolarized radar data is obtained using perturbation theory polarization coefficients while physical optics polarization predictions are observed at optical frequencies. Ambiguities in the comparisons between experimental data and model predictions are discussed.

Oscillation properties of anisotropic lasers

Abstract: Rate equations for anisotropic lasers were investigated theoretically. The effect of anisotropy of optical properties, such as emission cross section and resonant absorption loss, on the laser performance was examined quantitively. Conditions for dual-polarization oscillations (DPO), as well as formulas which relate the output power to the pump power and various other laser parameters, were given. Experiments were carried out using Nd-stoichiometric-laser crystals. There was good agreement between theory and experimental results. DPO laser oscillating mode patterns and output waveforms were also presented.

Direct measurement of gain recovery in a saturated Nd-glass amplifier

Abstract: The temporal dependence of the gain recovery in a Nd‐silicate glass amplifier has been directly observed after the passage of a short intense saturating laser pulse. The gain recovery time constant measured for ED‐2 glass is 1.25±0.2 nsec. A striking polarization dependence of gain saturation recovery is observed.

Optical emission in the radio lobes of radio galaxies

Abstract: We have found photographic and photometric evidence for optical emission in the radio lobes of 3C 285, 3C 265, and 3C 390.3. The optical luminosity of this emission lies between Bapprox.26 and Bapprox.22 mag arcsec/sup -2/. We discuss possible mechanisms of optical emission and their implications for models of radio galaxies. If the optical radiation arises from inverse Compton scattering of the blackbody background radiation, it provides a fairly direct method for measuring the magnetic fields in radio galaxies. For simple models, such fields would be below the equipartition value. If, on the other hand, the optical radiation is the visible extension of the radio synchrotron, it sets strong limits on the lifetimes of the relativistic electrons which must be regenerated in the extended source. We have examined several of the emission regions for optical polarization in order to help distinguish among these possiblities. These are all the radio galaxies which we have examined at the time of writing.

Search for X-ray polarization in the Crab pulsar.

Abstract: Results of a search for X-ray polarization in the Crab pulsar are presented which were obtained by observing the pulsar at 2.6 and 5.2 keV with identical X-ray polarimeters aboard OSO 8. The polarization in different portions of the X-ray light curve is analyzed, the polarization contribution due to the nebula is removed, and the results of the analysis are given for isolated portions of both the primary pulse and the interpulse at 2.6 and 5.2 keV. No evidence for X-ray polarization is found at the 99% confidence level; 3-sigma upper limits to the polarization at 2.6 keV are given along with the largest polarization allowed at 5.2 keV by the 99% confidence counter. It is noted that the trailing edge of the interpulse at 2.6 keV is 26% polarized at the 92% confidence level, while the 5.2-keV polarization measurement of 40% in the leading edge of the primary pulse is different from zero at 96% confidence. X-ray and optical polarization measurements are compared.

Imaging polarimetry of the jets of M87 and 3C 273

Abstract: Photoelectric polarization maps of the jets associated with M87 and 3C 273 are presented. For the M87 jet, polarization of individual knots reaches 20%. Comparison of the complex position angle structures at optical and radio frequencies (i) indicates the presence of a uniform (scale length> or approx. =1.5 kpc) medium in the vicinity of M87 which causes a Faraday rotation along the line of sight greater than approx.360rad m/sup -2/, and (ii) places an upper limit on the amount of Faraday depolarization occurring within individual knots.For the 3C 273 jet as a whole, our observations yield P=3.7% +- 4.1%. This measurement is consistent with inverse Compton models of the optical emission; however, a synchrotron origin cannot be excluded if the small-scale structure of the 3C 273 jet is similar to that of the jet of M87.

Excitation of Hg(6 3P1) by low energy alkali ion impact: Optical polarization and cross sections for magnetic sublevels

Abstract: Intensity and polarization of emitted light from collisions of ground state alkali ions and mercury atoms have been studied by a combined crossed‐beam and optical technique. Both the intensity and polarization of the Hg(6 3P1→6 1S0)−253.7 nm line exhibit a pronounced structure as a function of ion energy in the investigated range (from apparent thresholds to 3 keV); in particular, the polarization fraction takes on in succession very large positive and negative values. From the emission cross sections for several transitions, after correction for cascade and anisotropy, absolute cross sections for the excitation process M++Hg(6 1S0) →M++Hg(6 3P1), where M+=Li+, Na+, and K+, have been obtained. Using emission and polarization data, cross sections for population of the magnetic sublevels, mj=0 and ‖mj‖=1, have also been obtained. These cross sections have apparent thresholds much larger than the endoergicities of the processes, but reach very high values (of the order of 10−16 cm2) in the investigated energ...

Coordinated ultraviolet, optical, and radio observations of HR 1099 and UX Arietis

Abstract: Simultaneous radio, visual, and ultraviolet observations of the RS Canum Venaticorum binaries UX Arietis and HR 1099 are reported. The joint program covered the interval 1976 September 22 through October 3. The observations consisted of radio flux density measurements at 1660, 2695, and 8085 MHz; uv spectrophotometry of L..cap alpha.. and Mg II h and k; H..cap alpha.. and Ca II H and K spectroscopy; V-band photometry; and UBV polarimetry. A quasi-sinusoidal variation in V was observed in both systems. The period of this variation was approximately equal to the orbital period. No significant optical polarization was observed from either system. Variable radio emission was detected from both binaries throughout the program. Variable H..cap alpha.. and L..cap alpha.. emission were observed from HR 1099. UX Ari also exhibited L..cap alpha.. emission. Multiple Mg II emission components with peculiar velocities up to 250 km s/sup -1/ were often seen from both systems. Each Mg II observation also exhibited a strong and variable central velocity component which always seemed to match the orbital velocity of the more massive star in each system. HR 1099 exhibited strong Ca II H and K emission which was not significantly variable. The joint observations provide strongmore » evidence for chromospheric activity associated with the more massive star in each binary. Although the radio emission is produced in a larger volume than the optical and uv activity, temporal correlations suggest that a physical connection may exist between the two phenomena. 14 figures, 2 tables.« less

A passive nonresonant technique for pulse contrast enhancement and gain isolation

Abstract: A passive aperture‐scalable device is described which provides high contrast enhancement of a laser pulse over baseline optical noise while maintaining efficient net transmission of the principal laser pulse. The technique, which is based upon the nonresonant phenomenon of self‐induced ellipse rotation, is capable of providing effective gain isolation for virtually any high‐power laser system. The constrast enhancement capabilities of the device are demonstrated experimentally using a single ultrashort laser pulse obtained from a cavity‐dumped passively mode‐locked Nd : glass laser. In addition, a discussion is given concerning the ability of the device to temporally compress or stretch the optical pulse.

Giant Overhauser shift of conduction-electron spin resonance due to optical polarization of nuclei in semiconductors

Abstract: The hyperfine interaction with optically oriented electrons creates a nuclear polarization in $p$-type GaSb at 1.7 K, which is evidenced on the shift ${B}_{N}$ of the optically detected conduction-electron spin resonance (CESR). The experiments are performed in low external magnetic fields, where the nuclei are in a spin-temperature regime. In some samples the optically created nuclear polarization is so large that the shift ${B}_{N}$ of the CESR due to the polarized nuclei is larger than the external magnetic field. An electron-nuclear-double-resonance experiment has confirmed the nuclear origin of the observed effects. The existence of a spin temperature explains the experimental variation of ${B}_{N}$ with the electronic resonance frequency and the mean value of the electronic spin. We qualitatively interpret the variation of ${B}_{N}$ with the doping levels by assuming that the diffusion sphere around each donor contains the polarized nuclei. We evidence the importance of the quadrupolar interaction of nuclei to the impurity electric field gradients.

Photometry of AM Herculis: a slow optical pulsar?

Abstract: Multicolor photometry of the X-ray binary AM Her suggests that the red component of the optical flux is closely related to the source of optical circular polarization in the system. It is concluded from the periodic modulation of flux in the U through R bands, which is particularly well-defined when plotted as color curves, that the primary and secondary minima are neither eclipses by a secondary star nor eclipses by a hot spot. It is suggested that the primary minimum in the visual light curve is the eclipse of a region of intense optical emission in the magnetic field near the surface of a degenerate dwarf by that dwarf itself.

Synchrotron‐like radiation from intense laser beams in dense plasmas

Abstract: It is shown that when an intense, focused laser beam interacts with a dense plasma, relativistic effects may lead to observable synchrotron‐like x‐ray emission. For currently achievable Nd:glass laser intensities, the detectability of 10 keV x rays is expected to be enhanced by anisotropy of the source and by strong polarization.

Photoelectric polarization maps of two bipolar reflection nebulae.

Abstract: A rapidlt chopping polarimeter which uses a large-aperture Pockels cell and 200-element digicon detector has been constructed for mapping in two dimensions. This instrument has been used to obtain accurate, high-resolution maps of the optical polarization and surface brightness in the bipolar nebulae CRL 2688 and M1-92. Both nebulae reveal radially symmetric polarization patterns characteristic of reflection. The degree of polarization and comparison of the nebular surface brightness with the luminosity of the central star argue that, except for the NW lobe of M 1-92, the nebulae are optically thin to scattering. In addition, the very high polarization in CRL 2688 requires small scattering grains (a9 or approx. =0.1 ..mu..m). It follows that the stellar spectrum is substantially blued upon reflection and, by comparison of observed and intrinsic stellar colors, that a color excess E(B-V) approx. =1.7 is produced by circumstellar and interstellar extinction. We conclude that the visual extinction along the optical path of a scattered photon is approx.5 mag.The small grains, optical thinness, and symmetric geometry indicate that scattering by or transmission through a medium of aligned grains, rather than multiple scattering by randomly oriented stellar magnetic field at an angle to the axis of the nebula, couldmore » provide the necessary skew geometry. The grain masses of the scattering nebulae are found to be approx.10/sup -4/ M/sub sun/, comparable to those deduced from the IR emission of some planetary nebulae. We note the similarity in appearance between many planetaries and bipolar reflection nebulae and suggest that this structure may be explained by mass loss driven by nonradial pulsations.« less

Extending the field of view of KD*P electrooptic modulators

Abstract: The use of KD*P as a polarization rotator has been limited to small field of view instruments. To investigate this limitation, the index ellipsoid is used to describe the optical properties of KD*P and to calculate the retardance and fast axis as a function of the angle of incidence and voltage. Computed converging light patterns are then compared with observed intensity patterns formed by KD*P. Finally, computed intensity patterns are used to demonstrate how the field of view of KD*P can be increased when properly aligned with a positive uniaxial crystal.

Discovery of synchronous binary polarization in Cygnus X-1

Abstract: Using 180 nights of data from 1975 and 1977, we have found a stable polarization variation in the V band which is periodic on the orbital cycle of 5/sup d/.600. The peak-to-peak amplitude is 0.25% and is largely in the position-angle Stokes parameter. The amplitude in the ultraviolet is much smaller. The V-band polarization curves suggest a surprisingly large inclination; the single-scattering model gives i= (76 +- 8) /sup 0/. We also summarize our recent photometry.

Multimode 2 ? 2 optical crossbar switch

Abstract: A monolithic electro-optical 2 × 2 crossbar has been developed. The multimode network consists of channel waveguides and four crosspoint switches integrated in a LiTaO3 plate. Matrix switching loss was 11 dB and crosstalk was ?16 dB for TM-polarised 0.07-n.a. light.