Polarization Plane Of Radiation Research Articles

The Amplification and Polarization Control of Transmitted Radiation by a Graphene-Containing Photonic Cell

The transformation of the transmission spectra of linearly polarized radiation passing through a symmetric photonic cell is studied based on numerical analysis. The cell consists of two layers of magnetic semiconductor with a graphene monolayer on each and a central dielectric layer located between the graphene monolayers. It is possible to achieve amplification in the near terahertz range in graphene layers due to charge carrier drift. Control of transmission spectra and polarization of transmitted radiation can be achieved by changing the Fermi energy of graphene layers, by changing the external magnetic field, and by changing the thickness of the dielectric layer and the orientation of the incident radiation polarization plane.

Laser-induced linear dichroism in planar self-organized silver nanostructures

A method for obtaining metallic plasmonic nanostructures with linear dichroism, based on the method of burning out constant spectral dips, is proposed. Isotropic granular silver films obtained by physical vapor deposition in vacuum were irradiated with linearly polarized laser radiation in the spectral region of the plasmon resonance of their constituent nanoparticles. As a result of irradiation, the silver nanostructures change their sizes and shapes, and the films acquire a pronounced linear dichroism. Both the magnitude and the spectrum of linear dichroism depend on the state of the isotropic film before irradiation, which can be changed by heat treatment. For the unannealed films the dichroism does not change the sign over the entire spectral range studied and corresponds to the expected increase in the depth of the spectral dip for the light polarized parallel to the laser radiation polarization plane. For the annealed films, which consist of more distinctly formed and better separated nanoparticles, the dichroism value is greater, and the spectrum turns out to be sign-changing. The appearance of linear dichroism after laser irradiation is due to the differences in the change in the shape and size of the initially anisotropic nanoparticles that make up an isotropic film as a whole, depending on their orientation relative to the polarization plane of the laser beam. Keywords: plasmon resonance, silver nanostructures, linear dichroism, laser radiation.

Bloch-electron dynamics in homogeneous electric fields: Application to multiphoton absorption in semiconductors and insulators

The theory of Bloch-electron dynamics for carriers in a homogeneous electric field of arbitrary time dependence is developed in consideration of the properties of multiphoton absorption (MPA) in semiconductors and insulators. The general approach is to utilize the accelerated Bloch-state representation (ABR) as a basis thereby treating the electric field exactly; also, the electric field is described in the vector potential gauge. In developing the ABR, the instantaneous eigenstates for the central Hamiltonian are obtained as the accelerated Bloch states and utilized to find the time-dependent solution to the Schr\"odinger equation. In introducing the Wigner-Weisskopf approximation (WWA), the transition probability amplitude between the states of the system is obtained and used in the application to MPA in semiconductors and insulators. The probability amplitude for MPA is derived for a plane-polarized radiation field. The periodicity of the time-dependent electric field serves as a principle time constant in developing the probability amplitude per period. Utilizing the WWA, the general MPA transition probability is derived for transitions between an arbitrary set of valence and conduction bands for a time-varying electric field in the $x$ direction. Within the WWA, the MPA transition probability, equivalent to the well-known Keldysh transition amplitude, is derived and expressed in terms of infinite-variable generalized Bessel functions and modified Bessel functions. The exact MPA result is analyzed in the small ($\ensuremath{\lesssim}{10}^{6}$ V/cm) and large ($\ensuremath{\gtrsim}{10}^{8}$ V/cm) electric field amplitude limits.

Исследование возможности обнаружения оптических неоднородностей в тканях головного мозга по изображениям видимого и ближнего инфракрасного диапазонов

The possibility of detecting blood vessels located in the tissues of the brain, based on images of the visible and near infrared ranges, has been investigated. The preliminary results obtained in the course of the experiment confirm the prospects of using plane-polarized incoherent radiation with a central wavelength in the range from 730 to 900 nm in the course of further research in order to create a system for automatic detection of blood vessels and cranial nerves from endoscopic images.

In Vitro Investigation of Dental Enamel by Shift Interferometry

This study addresses investigations of dental tissue surfaces by in vitro shift interferometry. This work is relevant because use of this device for measuring the surface of dental enamel has high precision — to tenths of micrometers. The operation of a functional interferometer system is described. The criteria for adjustment of the device are given. Experimental results from determination of the surface roughness of a second molar treated with Tokuyama Bond Force II and in the natural state are presented. Measurement error of 0.1 μm was obtained for the treated sample, compared with 0.25 μm for the untreated sample. The measurement error due to the need to rotate the radiation polarization plane using a half-wave plate in one channel of the shift interferometer was estimated.

Helicity-induced shapes of resonant four-wave mixing responses from photofragments

Doppler profiles of the Degenerate Resonant Four-Wave Mixing (DFWM) spectral responses from rapidly recoiling products of photodecomposition by plane-polarized radiation are theoretically studied. Emphasis is placed on the shapes produced by rotational helicity when orientations of the angular momenta and the recoil velocities of nascent particles are correlated. Illustrations are provided for cases when a decay of resonating states tangibly affects the helicity-induced DFWM profiles.

Faraday effect on the Rb D 1 line in a cell with a thickness of half the wavelength of light

The rotation of the radiation polarization plane in a longitudinal magnetic field (Faraday effect) on the D1 line in atomic Rb vapor has been studied with the use of a nanocell with the thickness L varying in the range of 100–900 nm. It has been shown that an important parameter is the ratio L/λ, where λ = 795 nm is the wavelength of laser radiation resonant with the D1 line. The best parameters of the signal of rotation of the radiation polarization plane have been obtained at the thickness L = λ/2 = 397.5 nm. The fabricated nanocell had a large region with such a thickness. The spectral width of the signal reached at the thickness L = 397.5 nm is approximately 30 MHz, which is much smaller than the spectral width (≈ 500 MHz) reached with ordinary cells with a thickness in the range of 1–100 mm. The parameters of the Faraday rotation signal have been studied as functions of the temperature of the nanocell, the laser power, and the magnetic field strength. The signal has been reliably detected at the laser power PL ≥ 1 μW, magnetic field strength B ≥ 0.5 G, and the temperature of the nanocell T ≥ 100°C. It has been shown that the maximum rotation angle of the polarization plane in the longitudinal magnetic field is reached on the Fg = 3 → Fe = 2 transition of the 85Rb atom. The spectral profile of the Faraday rotation signal has a specific shape with a sharp peak, which promotes its applications. In particular, Rb atomic transitions in high magnetic fields about 1000 G are split into a large number of components, which are completely spectrally resolved and allow the study of the behavior of an individual transition.

Faraday isolator stably operating in a wide temperature range

A method of stabilizing Faraday isolator characteristics at varying temperatures is proposed in this letter. The method is based on the use of a magnetic system with an inhomogeneous magnetic field and a magneto-optical element holder made of a material with a high value of thermal expansion coefficient. Changing the rotation angle of the polarization plane of radiation caused by the temperature variation of the magneto-optical element and the temperature dependence of its Verdet constant is compensated by its shifting in the magnetic field. The developed device demonstrates an isolation ratio of more than 40 dB at a temperature range of 25 °C. Estimates show the possibility of providing an isolation ratio of more than 45 dB in a temperature range of 60 °C.

Features of faraday rotation in cs atomic vapor in a cell thinner than the wavelength of light

Features of the effect of Faraday rotation (the rotation of the radiation polarization plane) in a magnetic field of the D 1 line in Cs atomic vapor in a nanocell with the thickness L varying in the range of 80–900 nm have been analyzed. The key parameter is the ratio L/λ, where λ = 895 nm is the wavelength of laser radiation resonant with the D 1 line. The comparison of the parameters for two selected thicknesses L = λ and λ/2 has revealed an unusual behavior of the Faraday rotation signal: the spectrum of the Faraday rotation signal at L = λ/2 = 448 nm is several times narrower than the spectrum of the signal at L = λ, whereas its amplitude is larger by a factor of about 3. These differences become more dramatic with an increase in the power of the laser: the amplitude of the Faraday rotation signal at L = λ/2 increases, whereas the amplitude of the signal at L = λ almost vanishes. Such dependences on L are absent in centimeter-length cells. They are inherent only in nanocells. In spite of a small thickness, L = 448 nm, the Faraday rotation signal is certainly detected at magnetic fields ≥0.4 G, which ensures its application. At thicknesses L < 150 nm, the Faraday rotation signal exhibits “redshift,” which is manifestation of the van der Waals effect. The developed theoretical model describes the experiment well.

Optical detection in a ferromagnet

The detection of plane-polarized amplitude-modulated infrared laser radiation in a transparent yttrium-iron garnet ferromagnet at room temperature is performed experimentally. The nonlinear interaction mechanism is suggested. It is found that the magnitude and sign of the detected signal depend significantly on the magnetizing external magnetic field. The signal is observed when the magnetization of the ferromagnet approaches the saturated value. The measured dependence of the amplitude of the detected signal on the angle of polarization of the laser radiation with respect to the magnetization of the ferromagnetic sample supports the suggested nonlinearity mechanism. The largest nonlinearity appears when the magnetic field of the plane-polarized laser radiation is parallel to the magnetic moment of the magnetized ferromagnet.

Revealing cosmic rotation

Cosmological Birefringence (CB), a rotation of the polarization plane of radiation coming to us from distant astrophysical sources, may reveal parity violation in either the electromagnetic or gravitational sectors of the fundamental interactions in nature. Until only recently this phenomenon could be probed with only radio observations or observations at UV wavelengths. Recently, there is a substantial effort to constrain such non-standard models using observations of the rotation of the polarization plane of cosmic microwave background (CMB) radiation. This can be done via measurements of the $B$-modes of the CMB or by measuring its TB and EB correlations which vanish in the standard model. In this paper we show that $EB$ correlations-based estimator is the best for upcoming polarization experiments. The $EB$ based estimator surpasses other estimators because it has the smallest noise and of all the estimators is least affected by systematics. Current polarimeters are optimized for the detection of $B$-mode polarization from either primordial gravitational waves or by large scale structure via gravitational lensing. In the paper we also study optimization of CMB experiments for the detection of cosmological birefringence, in the presence of instrumental systematics, which by themselves are capable of producing $EB$ correlations; potentially mimicking CB.

Formation of relief gratings and refractive-index gratings on quartz glass under the action of a the radiation of a TEA CO2 laser*

This paper discusses how the profile of the residual surface relief of quartz glass in an irradiation spot depends on the number of active pulses of plane-polarized laser radiation with wavelength lambda = 10.6 µm. Based on experimental data, it is shown that an important role in the mechanism for forming periodic structures is played by the structural change of quartz glass subjected to melting and the associated change of its refractive index. Refractive-index gratings are detected in the near-surface layer of the glass in the total absence of periodic surface relief. When the radiation is normally incident, the period of the relief grating lies within the limits 8.9-9.1 µm, while the refractive-index grating lies within the limits 7.9-8.9 µm. These results agree with the model that explains the formation of the spatial modulation of radiation close to the surface of glass by the interference of the incident wave with surface phonon-polaritons. © 2004 Optical Society of America

Light transmission through the band gap bigyrotropic structure

The solution of Maxwell's equations in the case of electric and magnetic permeability tensor components periodically changing along the OZ axis has enabled an analysis of the passage of linearly polarized radiation through a bigyrotropic nonuniform structure with phase shift. With the assumption of a small modulation of the refractive index in the medium the dependence of the transmission factor is investigated. Its dependence on changes of medium parameters, length of the structure and incident wavelength is analysed. The change of ellipticity and orientation of the polarization plane of radiation passing through the specified structure is considered. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nonresonant multiphoton excitation spectra of atomic 7Li

The nonresonant multiphoton laser-induced fluorescence excitation spectrum of isotopically purified 7Li was obtained with a tunable, pulsed, nanosecond laser scanned between 13 600 and 14 500 cm–1. The measured Rydberg series include n 2P [Formula: see text] 2 2S, n 2F [Formula: see text] 2 2S, n 2P [Formula: see text]2 2P, and n 2F [Formula: see text] 2 2P, and term values up to 14 2P and 28 2F were determined. Features due to the ac Stark effect become prominent for the high Rydberg states, but can be eliminated by using circular instead of plane-polarized radiation. Quantum defect values for the n 2P, n 2D, and n 2F levels were determined. Those for the n 2F states cover a range of principal quantum numbers not previously investigated. PACS Nos.: 32.80Rm, 32.30Jc, 32.70Jz

Depolarization of X-ray laser radiation in plasmas due to various microscopic fluctuations

Two mechanisms of a depolarization of X-ray laser radiation in plasmas are studied. The first mechanism is produced by fluctuated magnetic microfield. Small areas (domains) of definited microfield amplitudes are working as elementary rotators of propagated radiation polarization plane. Passing a sequence of such domains, the radiation asquires a depolarized component. The second mechanism of depolarization is connected with different changes of the normal and tangential projections of the electric field vector of X-ray wave while the X-laser radiation passes the boundary between two media with different refractive indices N. Regions with different refractive indices exist due to the density fluctuations in plasmas (including microturbulence).

The Lineshape of Saturation-Broadened Transitions in the Gas Phase

The equations of motion for the density matrix are manipulated in spherical tensor form to derive formulas for the lineshapes of saturation-broadened spectroscopic transitions for gas-phase molecules. The formulas, which include consideration of the spatial degeneracy, are given for both plane-polarized and circularly polarized radiation and are in the form of weighted sums of the reciprocals of the eigenvalues of a matrix. In most practical cases, the eigenvalues will be in the form of Lorentz denominators, which expresses the lineshape as a sum of saturation-broadened Lorentz lineshapes. The approximations required to make the lineshapes equal to a sum of Karplus–Schwinger saturation-broadened lineshapes are described. The lineshape formula for plane-polarized radiation is equivalent to the continued-fraction form previously reported (R. H. Schwendeman, J. Chem. Phys. 73, 4838–4847 (1980)).

Polarization Modulation Effects in Infrared–Infrared Four-Level Double Resonance in13CH3F and15NH3

The elements of the Jones matrices for an optically pumped sample have been derived and used to predict four-level double resonance absorption coefficients that are functions of the velocity component of the molecules in the direction of the pump beam for different polarizations of the probe beam. When a saturating pump and weak probe are used in four-level double resonance experiments under population modulation conditions, these absorption coefficients are found to depend only on the first three statistical tensor ranks:n= 0 (population), 1 (orientation), and 2 (alignment). It is also found that for polarization modulation experiments with plane-polarized radiation, the absorption coefficient depends only on the alignment of them-state populations. Similarly, for polarization modulation with circularly polarized radiation, the absorption coefficient depends only on the orientation. The theory was used to interpret double-resonance polarization modulation experiments in13CH3F and15NH3in order to examine the effects of collisions on the initial anisotropy of the projection ofJon a space-fixedZaxis. The four-level double-resonance lineshapes were fit by least squares to absorption coefficients predicted by the theory. The collisional effects were modeled by a sum of Keilson–Storer collision kernels. The results of the fits were much improved when the value of the effective rate constant for the transfer of then= 0 tensor from the upper level of the pump to the lower level of the probe was larger than the values of the effective rate constants for the transfer of then= 1 and 2 populations. The best ratio of the rate constant forn> 0 to that forn= 0 is about 2/3 for13CH3F and 1/3 for15NH3. Additional analysis of the lineshapes showed the importance of long-range dipole–dipole interactions, elastic realignment and reorientation, and V–V mechanisms for collision-induced rotational energy transfer in13CH3F and15NH3.

Evolution of polarization in an inhomogeneous isotropic medium

The depolarization and rotation of the polarization plane of radiation propagating in a two-dimensional graded-index medium is investigated on the basis of the quantum-mechanical method of coherent states. It is shown that the degree of polarization of both linearly and circularly polarized radiation decreases with increasing distance as a result of interaction between the polarization (spin) and the path (orbital angular momentum) of the beam. The wave nature of the depolarization is emphasized. The depolarization decreases as the radiation wavelength decreases. It is found that the degree of polarization exhibits oscillations of pure diffraction origin during the propagation of light in a single-mode optical fiber. It is shown that the rotation of the polarization plane is nonuniform in character and depends on the offset and the tilt angle of the incident-beam axis relative to the fiber axis. The Berry phase is found to undergo oscillations of a wave nature during the propagation of radiation in an inhomogeneous medium. It is shown that the spread in the angle of rotation of the polarization plane increases with distance and can be determined from measurements of the degree of polarization of the radiation.

On the problem of polarization characteristics of radio waves in a randomly inhomogeneous magnetoactive plasma

Expressions for the Stokes parameters when radio waves propagate in a turbulent magnetoactive plasma have been obtained using a refractive scattering method. The problem of the spatial coherence of polarized radiation is considered. Expressions for the correlation functions and fluctuation dispersions of the Stokes parameters are found in the case of saturated wave field fluctuation. It is shown that the fluctuation of the circular polarized component will be observed in the received radiation even if the circular polarization is absent in the radiation that is incident on the magnetoactive plasma slab. A method is proposed to define the preference orientation of the magnetic field in the inhomogeneous layer of space plasma, which is biased on the simultaneous measurement of the space correlation functions of the I, V Stokes parameter fluctuation and Faraday rotation of the radiation polarization plane from the source with known polarization characteristics.

High-field Zeeman effect of shallow acceptors in germanium.

Zeeman absorption spectra have been obtained for B and Ga in Ge for B\ensuremath{\parallel}〈100〉 in the Voigt configuration with plane-polarized radiation. All twelve allowed transitions were observed for both the G and D lines. The corresponding excited states of these two lines for both impurities behave identically; two recent theoretical results are in good agreement. The measurements are a sensitive probe of the ground states; there are differences between the behavior of these for the two acceptors.