Oscillating Interference Pattern Research Articles

Passive depth estimation for a narrowband source using a single vector sensor in deep water.

For a narrowband signal, an oscillating interference pattern is formed with a target's moving when receiving at the bottom of the sea. In this Letter, the interference pattern of a narrowband source is observed using a single vector sensor (SVS). A passive depth estimation method employing a SVS is proposed. This approach processes the signals after the adaptive line enhancing and extracts the vector intensity, which oscillates periodically with the vertical azimuth. The passive estimation is achieved based on the Fourier-transform relationship between the depth and interference period. The simulation and sea experiment verify this method.

Numerical Analysis of the Transient Behavior of the Non-Equilibrium Quantum Liouville Equation

The numerical analysis of transient quantum effects in heterostructure devices with conventional numerical methods tends to pose problems. To overcome these limitations, a novel numerical scheme for the transient non-equilibrium solution of the quantum Liouville equation utilizing a finite volume discretization technique is proposed. Additionally, the solution with regard to the stationary regime, which can serve as a reference solution, is inherently included within the discretization scheme for the transient regime. Resulting in a highly oscillating interference pattern of the statistical density matrix as well in the stationary as in the transient regime, the reflecting nature of the conventional boundary conditions can be an additional source of error. Avoiding these non-physical reflections, the concept of a complex absorbing potential used for the Schrodinger equation is utilized to redefine the drift operator in order to render open boundary conditions for quantum transport equations. Furthermore, the method allows the application of the commonly used concept of inflow boundary conditions.

Optically Induced Space-charge and Conductivity Gratings in Wide-bandgap Semiconductors

We report optical excitation of space-charge and conductivity gratings in wide-bandgap semiconductors. The approach is based on the illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current results from the periodic relative shifts of the photoconductivity and space charge electric field gratings which arise in the volume of the crystal under illumination. The experiments are carried out in β-Ga2O3 crystal and the main parameters of the photoinduced carriers are determined.

Space-and-time current spectroscopy of nanostructured selenium in the chrysotile asbestos matrix

The non-steady-state photoelectromotive force effect was experimentally studied in a semiconductor nanowire array, i.e., in a composite representing selenium in a chrysotile asbestos matrix. The sample was exposed to an oscillating interference pattern, and the material response was measured as an alternating electric current. The experiments were performed for two geometries in which the excited photocurrent was parallel or perpendicular to nanowires. The dependences of the signal amplitude on the phase modulation frequency, spatial frequency, light polarization, and temperature were obtained. The photoelectric parameters of the material were determined for the light wavelength λ = 633 nm. The effect was theoretically analyzed for the semiconductor model with shallow traps, which allowed the explanation of the observed increase in the signal amplitude in the presence of additional phase modulation.

Influence of a Time-Dependent Applied Electric Field on the Photocurrent in Photorefractive Materials

From the differential material rate equations, we found an additional term to the usual expression of the photocurrent, which appears only when a time-dependent external electric field is applied. This term influences the photocurrent in the material. We applied our equations to a Bi12SiO20 sample, under an applied sinusoidal electric field. This sample is illuminated with an oscillating interference pattern formed by two plane light waves, one of which is phase-modulated with frequency ω. We found good agreement with experimental results. Besides, for this case, our prediction for the photocurrent is better than the usual prediction of the photocurrent for low values of ω.

Non-steady-state photoelectromotive force in an AlN crystal

We report the experimental investigation of the non-steady-state photoelectromotive force in aluminum nitride crystal. The sample is illuminated by an oscillating interference pattern formed by two coherent light beams and the alternating current is detected as a response of the material. The experiments are performed for two geometries, where arising photocurrent is parallel or perpendicular to the optical axis of the crystal. Dependencies of the signal amplitude versus light intensity, and temporal and spatial frequencies are measured. The photoelectric parameters of the material are estimated for the light wavelength $\ensuremath{\lambda}=532$ nm.

Excitation of electric-field-driven spin remagnetization waves on a cylindrical surface with spin–orbit interaction

Elementary excitations of a two-dimensional electron gas confined to a cylindrical surface are theoretically studied on the basis of coupled spin-charge drift-diffusion equations. The electric-field-mediated eigenmodes can be optically excited by an oscillating interference pattern. For a cylinder with a given radius, weakly damped resonances due to spin remagnetization waves are identified in the steady-state charge current response.

Characterization of CdTe, Cd xZn 1−xTe and GaAs detectors

We report space-and-time current spectroscopy for characterization of high-quality GaAs thin films grown on semi-insulating gallium arsenide substrates. The approach is based on illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current resulted from the periodic relative shifts of the photoconductivity and space charge electric field gratings arising in the crystal's volume under illumination. The results of measurements of semiconductor material's parameters of CdTe and Cd x Zn 1− x Te detectors are presented. The experiments are carried out for the diffusion regime of signal excitation at light wavelength λ=1.15 μm. The sign, conductivity and diffusion length are estimated from the dependencies of the signal on the temporal and spatial frequencies. The high-quality GaAs thin films grown on semi-insulating gallium arsenide substrates are characterized. The experiments are carried out in the geometry of the Michelson interferometer at the illumination wavelength of 532 nm. The dependence of the non-steady-state photocurrent on spatial frequency of the interference pattern is measured, allowing estimation of the diffusion length of photoelectrons in GaAs thin film L D=40 μm.

Non-steady-state photo-EMF in nanostructured GaN and polypyrrole within porous matrices

We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10−10 Ω−1 cm−1 (λ=442 nm, I0=0.045–0.19 W/cm2, T=293 K) and σ=(3.5–4.6)×10−10 Ω−1 cm−1 (λ=532 nm, I0=2.3 W/cm2, T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: LD=0.18 μm.

Non-steady-state photo-EMF in nanostructured GaN within porous glass matrix

Abstract We report the experimental investigation of the non-steady-state photoelectromotive force in porous glass filled with GaN nanoparticles. The sample is illuminated by an oscillating interference pattern created by two coherent light beams and the alternating current is detected as a response of the material. Dependencies of the signal amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ = 442 , 532 nm. The conductivity of the material is measured: σ = ( 1.1 – 1.6 ) × 10 - 10 Ω - 1 cm - 1 ( λ = 442 nm , I 0 = 0.045 – 0.19 W / cm 2 , T = 293 K ) and σ = ( 3.5 – 4.6 ) × 10 - 10 Ω - 1 cm - 1 ( λ = 532 nm , I 0 = 2.3 W / cm 2 , T = 249 – 388 K ) .

Excitation of spin waves on a cylindrical semiconductor heterostructure with Rashba spin–orbit interaction

Elementary excitations in a paramagnetic semiconductor quantum well confined to a cylindrical surface are theoretically studied on the basis of coupled spin–charge drift–diffusion equations. The electric field-mediated eigenmodes are optically excited by an oscillating interference pattern, which induces a current in the outer circuit. For a cylinder with a given radius, sharp resonances are predicted to occur in the steady-state current response, which are due to weakly damped spin remagnetization waves.

Optical excitation of space-charge waves involving interband transitions in Bi12GeO20 Crystals

The excitation of space-charge waves in a semiconductor (B12GeO20) crystal using light with photon energy close to the bandgap width has been studied. The sample crystal has been optically excited by exposure to an oscillating interference pattern. The existing model notions are consistent with the experimental results.

Excitation of spin remagnetization waves in systems with spin-orbit coupling

Elementary excitations of a new type in paramagnetic materials with spin-orbit interaction are predicted theoretically within the Rashba model and named the spin remagnetization waves. These normal modes arise from rotation of the spin magnetic moment in a medium where the electric field contains a constant component and a traveling wave component. A method is proposed for exciting these vibrations by illuminating the sample with an oscillating interference pattern. The spin remagnetization waves can be experimentally detected by measuring the dependence of the current through the sample on the oscillation frequency and wave vector of the interference pattern.

Detection of dynamic population gratings in erbium-doped optical fibers by means of transient fluorescence excited by oscillating interference pattern

We report a new, to the best of our knowledge, method for detection of dynamic population gratings in Er-doped fibers with saturable absorption that is based on observation of the transient fluorescence resulting from fast displacement of the recording interference pattern. The signal appears due to essentially different relaxation times of the fluorescence in bright and dark fringes of the light pattern. The experimental results obtained at the recording wavelength λ=1492 nm in a single-mode fiber with 5600 ppm Er demonstrate good agreement with the theoretical model based on a saturable two-level system. Unlike conventional diffraction-based techniques, the proposed method results in the local grating amplitude value and can be used for characterization of the grating amplitude spatial profile. It can also be suitable for characterization of the grating formation processes in other bulk and thin-film media with saturable absorption.

Space-and-time current spectroscopy of GaAs-based detectors

We report space-and-time current spectroscopy for characterization of high-quality GaAs thin films grown on semi-insulating gallium arsenide substrates. The approach is based on illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current is resulted from the periodic relative shifts of the photoconductivity and space charge electric field gratings, which arise in the crystal's volume under illumination. The experiments are carried out in the geometry of Michelson interferometer at the illumination wavelength of 532 nm. The dependence of the non-steady-state photocurrent on spatial frequency of the interference pattern is measured allowing estimation of the diffusion length of photoelectrons in GaAs thin film L D=40 μm.

Space-and-time current spectroscopy of wide-gap semiconductors

We report space-and-time current spectroscopy for characterization of wide-gap semiconductors. The approach is based on the illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current results from the periodic relative shifts of the photoconductivity and space charge electric field gratings which arise in the volume of the crystal under illumination. The experiments are carried out in photorefractive n-type Bi12SiO20, molecular SnS2 and pyrolytic crystal of BN and the main parameters of the photoinduced carriers are determined.

Interaction of running gratings of the space charge and conductivity in photorefractive Bi12Si(Ti)O20 crystals

The simultaneous excitation and nonlinear interaction of the space-charge and photoconductivity gratings are studied experimentally in photorefractive Bi12SiO20 and Bi12TiO20. The measurements are performed using the diffraction technique, which implies the illumination of the crystal by an oscillating interference pattern (λr=532 nm) along with the application of dc and ac electric fields and detection of the diffracted probe beam (λp=650 nm). Such illumination excites the running photoconductivity grating, which interacts with the ac component of the applied field giving rise to the space-charge wave. Being the eigenmode of the space-charge oscillations, this wave reveals itself as a low-frequency resonant maximum at the frequency-transfer function of the detected signal. The drift mobilities of electrons are estimated using the developed technique: μ=(1.1–1.4) ×10-2 cm2/V s (Bi12SiO20, T=296–298 K) and μ=2.8×10-3 cm2/V s (Bi12TiO20, T=293 K).

Nonlinear interaction of moving space-charge and photoconductivity gratings in Bi12SiO20 crystal

A nonlinear interaction of moving space-charge and photoconductivity gratings is experimentally investigated. In the presence of a dc electric field, a crystal is irradiated with an oscillating interference pattern with a spatial frequency K and an oscillation frequency ω. An ac electric field with a frequency \gM is also applied to the sample. At certain frequencies ω and \gM, the crystal exhibits two types of interacting oscillations: the space-charge grating moving with velocity |ω−Ω|/K and the photoconductivity grating moving with velocity −ω/K. The effect is studied using the method of the nonstationary photoelectromotive force in a photorefractive Bi12SiO20 crystal.

Dynamic electrooptic effect induced by space charge waves in sillenites

Abstract In photorefractive sillenite-type crystals we discovered that a temporally oscillating but spatially homogeneous space charge field arises if we illuminate the samples with a spatially oscillating interference pattern formed by two coherent plane light waves. This field is of the order of 50–60 V/cm and we investigate it via measurements of its influence on the state of polarization of a transmitted probe beam, i.e., via the dynamic electrooptic effect which is induced by this spatially homogeneous space charge field. It is shown that the reason for the occurrence of the space charge field is a nonlinear interaction of space charge waves. Very good agreement between the experimental data and results of the proposed theoretical model is demonstrated.

Dynamic bulk photovoltaic effect in photorefractive barium calcium titanate

Oscillating photocurrents are generated in a photorefractive iron-doped barium calcium titanate crystal (Ba0.77Ca0.23TiO3; BCT) by illumination with an oscillating interference pattern. Non-steady-state photocurrents arise usually from the interaction of a space-charge field with an oscillating photoconductivity pattern. However, a second-harmonic signal of the oscillating photocurrents is observed in BCT, which is present without any space-charge field. The main features of the new effect can be explained by consideration of a dynamic, i.e., time-dependent, bulk photovoltaic effect. The effect might be useful for optically addressed memories or optical correlators.