Longitudinal Polarization Mode Research Articles

Shining massive light through a wall

A massive photon possesses a longitudinal polarization mode absent in its massless counterpart. Transverse and longitudinal modes follow different dispersion relations, the latter being much less attenuated than the former when passing through a conductor, suggesting the possibility of isolating longitudinal modes by shining intense light on a conducting wall. We calculate the transmission rates for normal incidence upon a semi-infinite medium and passage through a slab. For the second case we compare the expected photon fluxes with those measurable in current and future light-shining-through-a-wall experiments. Using a 1-MW microwave source as envisaged by the STAX project, a sensitivity at the level of $m_\gamma < 9.6 \times 10^{-11} \, {\rm eV/c^2}$ could be reached after a run time of an year, with a potential improvement by a factor of $\sim 10^4$ if radio waves of similar power are used.

Raman scattering of light in single crystals of lithium niobate co-doped with copper and gadolinium

The conditions for the excitation of transverse and longitudinal polar modes in the processes of Raman scattering in lithium niobate single crystals with co-doped with copper and gadolinium are established using a backscattering geometry. A significant increase in the intensity of the Raman lines at 175 and 603 cm−1 was found with an increase in the degree of doping of the crystals with copper due to the photorefractive effect.

Growth, microstructure and optical characteristics of doped LiNbO3:Gd and LiNbO3:Cu:Gd lithium niobate crystals

Double- and single-doped lithium niobate (LN) crystals were grown by Czochralski at air from platinum crucibles: sample 1 ([Cu] = 0.57, [Gd] = 0.07 wt%), sample 2 ([Cu] = 0.041, [Gd] = 0.076 wt%), sample 3 ([Gd] = 0.003 wt%), sample 4 ([Gd] = 0.01 wt%), sample 5 ([Gd] = 0.05 wt%) and sample 6 ([Gd] = 0.26 wt%). Macro- and microstructure of as-grown LiNbO3:Cu:Gd and LiNbO3:Gd crystals have been studied by optical microscopy. Laser conoscopy, photoinduced light scattering (PILS) and optical spectroscopy have studied optical transmission, optical uniformity and photorefraction in LN crystals. Such a composition have been determined for a four-component system Li2O–Nb2O5–CuO—Gd2O3, at which a highly compositionally and optically uniform LiNbO3:Cu:Gd crystal (sample 2, [Cu] = 0.041, [Gd] = 0.076 wt%) can be grown. Raman spectra in 180-grade scattering geometry have determined conditions for the excitation of transverse and longitudinal polar modes during Raman scattering in LiNbO3:Cu:Gd crystals. A great increase in 175 and 603 cm−1 Raman bands intensities has been detected at an increase in copper concentration; it has been explained as a manifestation of photorefractive effect.

Non-tensorial gravitational wave background in NANOGrav 12.5-year data set

We perform the first search for an isotropic non-tensorial gravitational-wave background (GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 12.5-year data set. By modeling the GWB as a power-law spectrum, we find strong Bayesian indication for a spatially correlated process with scalar transverse (ST) correlations whose Bayes factor versus the spatially uncorrelated common-spectrum process is 107 ± 7, but no statistically significant evidence for the tensor transverse, vector longitudinal, and scalar longitudinal polarization modes. The median and the 90% equal-tail amplitudes of ST mode are $$\cal{A}_{\text{ST}}=1.06_{-0.28}^{+0.35}\times10^{-15}$$ , or equivalently the energy density parameter per logarithm frequency is $$\Omega_{\text{GW}}^{\text{ST}}=1.54_{-0.71}^{+1.21}\times10^{-9}$$ , at frequency of 1/year.

Polar modes and overtone states in Raman spectra of lithium tantalate crystals

The conditions for the excitation of transverse and longitudinal polar modes in the processes of Raman scattering of light in mono- and polydomain lithium tantalate single crystals are established using a backscattering geometry. The relative intensity of the overtone Raman spectrum on the longitudinal and transverse fundamental polar excitations is much higher in the polydomain sample. Unfortunately, the exact reason for the difference in the Raman spectra of the mono- and polydomain lithium tantalate samples is unknown. The frequencies of the two overtone bands exceeded the exact value of the overtone frequency corresponding to the fundamental longitudinal polar mode $4{A}_{1}(\text{LO})$, which clearly indicates the existence of bound phonon pairs (biphonons). This is consistent with theory and has been shown for both mono- and polydomain samples. On the basis of the general theory of bound states of quasiparticles, the possibility of the existence of bound states of quadrupole excitations of the antipolar type in the vibrational spectrum of a polydomain crystal of lithium tantalate is predicted.

Study of b⟶c Induced B¯∗⟶Vℓν¯ℓ Decays

In this paper, we investigate the tree-dominated B¯u,d,s,c∗⟶Vℓ−ν¯ℓ (V=Du,d∗,Ds∗,J/ψ and ℓ=e,μ,τ) decays in the Standard Model with the relevant form factors obtained in the light-front quark model. These decays involve much more helicity states relative to the corresponding B¯∗⟶Pℓ−ν¯ℓ and B¯⟶Vℓ−ν¯ℓ decays, and moreover, the contribution of longitudinal polarization mode (V meson) is relatively small, ~30%, compared with the corresponding B meson decays. We have also computed the branching fraction, lepton spin asymmetry, forward-backward asymmetry, and ratio RV∗L≡BB¯∗⟶Vτ−ν¯τ/BB¯∗⟶Vℓ′−ν¯ℓ′ℓ′=e,μ. Numerically, the branching fractions of B¯∗⟶Vℓ′−ν¯ℓ′ decays are at the level of O10−7 and are hopeful to be observed by LHC and Belle-II experiments. The ratios RD∗,Ds∗,J/ψ∗L have relatively small theoretical uncertainties and are close to each other, RD∗∗L≃RDs∗∗L≃RJ/ψ∗L≃0.26,0.270.27,0.29, which are a bit different from the predictions in some previous works. The future measurements are expected to make tests on these predictions.

The description of gravitational waves in geometric scalar gravity

It is investigated the gravitational waves phenomena in the geometric scalar theory of gravity (GSG), a class of theories such that gravity is described by a single scalar field. The associated physical metric describing the spacetime is constructed from a disformal transformation of Minkowski geometry. In this theory, a weak field approximation gives rise to a description similar to that one obtained in general relativity, with the gravitational waves propagating at the same speed as the light, although they have a characteristic longitudinal polarization mode, besides others modes that are observer dependent. We also analyze the energy carried by the gravitational waves as well as how their emission affects the orbital period of a binary system. Observational data coming from Hulse and Taylor binary pulsar is then used to constraint the theory parameter.

Published Tunneling Results of Binnig et al Interpreted as Related to Surface Superconductivity in SrTiO3

In 1980, Binnig et al. reported tunneling measurements on Nb-doped SrTiO3, and interpreted their results as indicating two-band superconductivity in the bulk of SrTiO3. However, (1) effective masses determined from tunneling results in the normal state by Sroubek in 1969 and 1970 are much smaller than those determined by most other methods. The much smaller masses were attributed to properties of a surface layer by the present author in 1971. (2) The only other reports of two-band superconductivity in bulk SrTiO3 can be used to infer much smaller values for the band separations than found by Binnig et al. In this paper, we give an alternative explanation of the results of Binnig et al. in terms of superconductivity in a surface layer. We obtain fair fits to the band gaps versus Fermi energy for the two bands in the three samples where two surface subbands are occupied and to the temperature dependence of the gaps in one crystal, using a model with three adjustable interaction parameters, an adjustable energy for the phonons which dominate the pairing, and an adjustable ratio of the mean-field T c to the actual T c . We show results for a combined fit to the low-temperature band gaps and to the T-dependence in one crystal. The phonon energy which gives the best fit is 21 meV. This is probably an appropriate average over the three longitudinal polar modes and acoustic modes in the material. A large value of about two is found for the ratio T c m f /T c , and we conjecture that this arises because a band with a small Fermi energy, not seen in the tunneling results, plays a part in increasing T c m f /T c .

Silicon nanorods‐based all‐dielectric waveguides with long decay‐length at the telecommunication band

AbstractWe investigate subwavelength waveguides composed of silicon nanorods array in straight and nonstraight regimes deposited on a silica (SiO2) substrate. It is shown that using all‐dielectric nanorods with high permittivity to design an all‐dielectric optical waveguide provides several advantages such as low‐dissipation coefficient and long decay length for the distributed fields. Exploiting silicon arrays in touching and nontouching arrangements, we examined the optical response of the structure to the guiding of magnetic and electric fields with transverse and longitudinal polarization modes. We studied the decay length for all propagated modes in both nanochain orientations numerically. Simulation results for straight arrays showed that the averaged decay length for the structure with dielectric particles in touching regime is 1.6 µm (for the waveguide with the length of 2.2 µm), and for the nontouching array is 2.2 µm (for the array with the length of 3.1 µm). Calculating transmission loss factors and considering decay length of the proposed waveguide, we verified the strong potential of the proposed structure to design all‐dielectric photonic devices to operate at telecommunication spectra (λ~1310 nm and 1550 nm). Also, we computed bending losses [dB] for the examined structures based on the bends degree. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Plasmon resonance excitation and near-field manipulating in gold nanopyramid arrangements at the telecommunication spectrum

In this work, we investigated the optical characteristics of a gold nanopyramid with certain geometrical dimensions to generate surface plasmons inside it at the near infrared region. The approximate geometrical sizes for all of the revisable dimensions have been computed based on the position and peak of the plasmon resonance at wavelength 1550 nm. The influence of absorption and scattering of light as dissipative and lossy components on the optical response of the non-spherical configuration have been discussed numerically. Employing the examined pyramid in a chain, we measured the quality of the near-field coupling between series pyramids, and the optical properties of the provided plasmon waveguide have been determined. Moreover, the group velocity of guided waves and transmission loss factors along the nanostructure have been quantified as υgT=0.23c0, υgL=0.41c0 and γT=3 dB/452 nm, γL=3 dB/312 nm for transverse and longitudinal polarization modes, respectively. The finite-difference time-domain method has been utilized as a major solution to extract the optical properties of the proposed configurations.

Analysis of the Raman gain distribution as a technique to determine longitudinal PMD distribution in optical fibers

In this paper, we present and analyze a new longitudinal polarization mode dispersion distribution indicator technique based on the longitudinal Raman gain distribution measurement by OTDR. Measurement principles are presented along with experimental results obtained in two fibers with different PMD values.

Additional Raman Scattering Mechanism due to Transverse Polar Modes**The project supported by National Natural Science Foundation of China under Grant No. 19847004

Longitudinal polar modes generate a macroscopic electric field in piezoelectric crystals and cause an additional mechanism of Raman scattering. The classical theory holds that transverse polar modes cannot produce such an additional mechanism. Our quantum theory shows that there is an additional Raman scattering mechanism arising from the electro-optic effect of transverse polar modes.

Electrostatic spectrum of renormalized polarizability for nonpolar dielectric

The Drude–Lorentz model of a nonpolar dielectric with the simple cubic, face-centered and body-centered crystal lattice structures is considered. The electrostatic spectral density of the renormalized polarizability is found. The problem is equivalent to the calculation of the electronic density of states in the model. The obtained spectra are analyzed and the critical points are identified. The results are compared with the computer simulation data for a hard-sphere fluid. In the latter, the structure analogous to the transverse and longitudinal polarization modes characteristic for a solid dielectric is shown to exist.

Theory of Transitions from Large to Nearly-Small Polarons, with Application to Zr-Doped Superconducting SrTiO3

Expressions for the matrix elements of the Hamiltonian and overlap integrals between large-polaron and nearly-small-polaron states are given in terms of various large- and nearly-small-polaron parameters. The dependence of the mass of the ground state on the bare-electron mass in a region of transition between large- and nearly-small-polaron states is found. Parameters of the theory are evaluated using the continuum-polarization model of electron-phonon interactions. Modifications due to anisotropy and the presence of many longitudinal polar modes of lattice vibration are discussed briefly. Making use of a recent analysis by Reik of free-carrier optical-absorption results in SrTi${\mathrm{O}}_{3}$ using small-polaron theory, it is shown that the rate of mass rise deducible from superconductivity data on Zr-doped SrTi${\mathrm{O}}_{3}$ can be explained by the theory if the bare transverse mass ${m}_{\mathrm{bt}}$ is taken to be ${m}_{\mathrm{bt}}\ensuremath{\simeq}0.6{m}_{e}$, where ${m}_{e}$ is the free-electron mass, and if small-polaron binding energies are assumed to be larger by a factor of about 1.4 than their values in the continuum-polarization model. The dependence on Zr concentration of the ratio of phonon-induced to Coulomb intervalley electron-electron interactions deducible from the superconductivity data is discussed within the framework of the model.

Free Carrier Absorption Due to Polar Modes in the III-V Compound Semiconductors

The longitudinal polar modes of vibration in the III-V compound semiconductors play an important part in determining their transport properties, such as mobility. One would therefore expect them to be important for free carrier absorption, as well, in these semiconductors. A quantum mechanical calculation of the free carrier absorption arising from these modes has been made and gives an absorption varying as ${\ensuremath{\lambda}}^{2.5}$, and such behavior has been reported experimentally in InP and GaP. The calculated value of the absorption coefficient in InP is in good agreement with experiment.