Field Interference Pattern Research Articles

Phase dual-resolution networks for a computer-generated hologram.

The computer-generated hologram (CGH) is a method for calculating arbitrary optical field interference patterns. Iterative algorithms for CGHs require a built-in trade-off between computation speed and accuracy of the hologram, which restricts the performance of applications. Although the non-iterative algorithm for CGHs is quicker, the hologram accuracy does not meet expectations. We propose a phase dual-resolution network (PDRNet) based on deep learning for generating phase-only holograms with fixed computational complexity. There are no ground-truth holograms employed in the training; instead, the differentiability of the angular spectrum method is used to realize unsupervised training of the convolutional neural network. In the PDRNet algorithm, we optimized the dual-resolution network as the prototype of the hologram generator to enhance the mapping capability. The combination of multi-scale structural similarity (MS-SSIM) and mean square error (MSE) is used as the loss function to generate a high-fidelity hologram. The simulation indicates that the proposed PDRNet can generate high-fidelity 1080P resolution holograms in 57 ms. Experiments in the holographic display show fewer speckles in the reconstructed image.

Numerical modeling of the sound field interference pattern in the presence of intense internal waves

The purpose of the paper is numerical modeling of the sound field in the presence of intense internal waves to study the interference pattern in inhomogeneous ocean waveguide. It is assumed that intense internal waves are the reason for the sound field modes coupling and horizontal refraction. The results of sound field modeling are processed to obtain acoustic intensity distributions in the frequency-time domain (interferogram) for unmoving sources. The two-dimensional Fourier transform (2D-FT) is applied to analyze the interferogram. The result of the 2D-FT can be called the Fourier-hologram (hologram). The hologram allows us to coherently accumulate the sound intensity of the interferogram in the narrow area as focal spots. It is demonstrated in the paper that the position of focal spots in the hologram depends on the distance between the source and the receiver. The relationship between the interferogram and hologram structures and the unperturbed and scattered fields parameters is obtained in the paper. The hologram spectral density consists of the two disjoint regions corresponding to the scattered and scattered fields. The filtering of these areas allows us to transmit the non-distorted information through an inhomogeneous ocean environment. The numerical simulation results of interferograms and holograms in the presence of the internal waves are considered. [This research was supported by the RFBR (19-29-06075, 19-38-90326).]

Single-shot spatial coherence characterization of x-ray ultrafast sources.

Spatial coherence is an impactful source parameter in many applications ranging from atomic and molecular physics to metrology or imaging. In lensless imaging, for example, it can strongly affect the image formation, especially when the source exhibits shot-to-shot variations. Single-shot characterization of the spatial coherence length of a source is thus crucial. However, current techniques require either parallel intensity measurements or the use of several masks. Based on the method proposed by González et al. [J. Opt. Soc. Am. A28, 1107 (2011)JOAOD60740-323210.1364/JOSAA.28.001107], we designed a specific arrangement of a two-dimensional non-redundant array of apertures, which allows, through its far field interference pattern, for a single-shot measurement of the spatial coherence, while being robust against beam-pointing instabilities. The strategic configuration of the pinholes allows us to disentangle the degree of spatial coherence from the intensity distribution, thus removing the need for parallel measurement of the beam intensity. An experimental validation is performed using a high-harmonic source. A statistical study in different regimes shows the robustness of the method.

Optimization of a multibeam-pumped optical parametric amplifier.

The results of numerical simulation of the output amplifier cascade of a powerful laser system based on the parametric amplification of femtosecond pulses in an LiB3O5 crystal with multiple beams pumping are presented. The improved technique for choosing pump beam angles with minimal parasitic amplification is presented. Differences of carrier-resolving versus envelope simulations are discussed. Results for pulse energy, duration, and fraction of parasitic energy are presented. It has been established that with an increase in the number of pump beams up to 11 beams, the duration of the amplified pulse increases insignificantly from 20 to 21fs in the case of incoherent pumping beams and increases to 26fs in the case of coherent ones. At the same time, the amplification efficiency decreases from 23% to 21% in the first case and drops to 10% in the second case. Influence of small-scale, self-focusing of the pump field interference pattern on peak intensity is discussed.

Variability of the sound field interference pattern due to horizontal refraction in shallow water

Variability of the ocean waveguide’s parameters in horizontal plane (bathymetry, sound speed profile, etc.) can lead to some set of effects in the sound propagation, which are specified as horizontal refraction, or in more general form, as 3D effects. These effects are being studied both in shallow and deep water, some of them were registered in experiments, or were analyzed using different theoretical models. In given paper main attention is drawn to the theory and experimental manifestation of spatial and temporal variations of interference pattern formed by narrow-band signals. Theoretical analysis is carried out using approach “Vertical Modes and Horizontal Rays” and “Vertical Modes and PE in horizontal plane.” It is shown, that dependence of the sound field distribution in horizontal plane (both in a ray or PE approaches) on frequency and mode number, combined with possible multipath propagation, may lead to rather specific observable effects: variations of the amplitude and phase fronts, evolution o...

Passive coherent combination of a diode laser array with 35 elements

A monolithic diode laser array with 35 elements is operated as a coherent array through the use of a Self-Fourier cavity. By analyzing the far field interference pattern, the coherence was measured to be 0.57 with all 35 elements operating and was measured to be approximately constant for arrays with greater than 15 elements. These results are in rough agreement with previous analyses which predict a coherence equal to 0.65 for very large arrays of passively coupled laser elements and demonstrate how the use of regenerative feedback benefits the passive phasing of coherent laser arrays. These results demonstrate that it is possible to circumvent previous cold cavity theories that predict poor phasing properties for arrays with greater than ~10 elements.

Frequency shifts of the sound field interference pattern in shallow water because of second-mode soliton-like internal waves

Numerical simulation is carried out to analyze the effect of an internal soliton of the second gravity mode on low-frequency sound propagation in an oceanic shelf region. The simulation is performed using the data of a full-scale experiment performed on the shelf of the South China Sea near Dongsha atoll, where the aforementioned solitons had been detected by stationary vertical thermistor arrays. The calculations take into account the effect of horizontal refraction of sound waves. It is assumed that a stationary acoustic track is oriented across the predominant propagation direction of internal waves. The results of simulation show that, when the soliton crosses the stationary track, some of the sound field modes are focused, whereas other modes are defocused. It is demonstrated that the soliton parameters can be adequately determined from the frequency shifts of the sound field interference pattern. However, such an estimate of the soliton parameters is only possible for a limited length of the stationary track for which the effect of horizontal refraction is sufficiently weak.

Frequency shifts of the sound field interference pattern on oceanic shelf in summer conditions

Considerable shifts Δf/ϕ ≈ 10−1 of the low-frequency sound field interference pattern in the frequency domain, associated with barotropic tide and internal tidal waves, were observed in the Shallow Water’06 experiment on the New Jersey shelf in the summer of 2006. The acoustic frequency shifts appear to be strongly dependent on the modes of the sound field. By examining different modal structure, it is possible to analyze the overall interference pattern and find which part is more sensitive either to the surface tide or the internal waves. This feature can be exploited to acoustically monitor tidal waves of different kinds.

Coherent Beam Combining of Two Fiber Amplifiers Seeded by Multi-Wavelength Fiber Laser

Multi-wavelength seed laser can mitigate stimulated Brillouin scattering (SBS) and improve the output power of the narrow-linewidth fiber amplifier. In this present study, coherent combining of two fiber amplifiers seeded by a multi-wavelength laser is proposed and demonstrated using stochastic parallel gradient descent (SPGD) algorithm. The long-exposure visibility of the far field interference pattern is increased from 0.15 to 0.97 when the system evolves from open-loop to closed-loop. The feasibility of coherent combining of fiber amplifiers seeded by multi-wavelength seed laser is validated.

X-Ray Nanointerferometer Based on Si Refractive Bilenses

We report a novel type of x-ray interferometer employing a bilens system consisting of two parallel compound refractive lenses, each of which creates a diffraction limited beam under coherent illumination. By closely overlapping such coherent beams, an interference field with a fringe spacing ranging from tens of nanometers to tens of micrometers is produced. In an experiment performed with 12 keV x rays, submicron fringes were observed by scanning and moiré imaging of the test grid. The far field interference pattern was used to characterize the x-ray coherence. Our technique opens up new opportunities for studying natural and man-made nanoscale materials.

Coherent beam combination of two fiber amplifiers with multi-dithering technique

Coherent beam combination of two W-level fiber amplifiers with multi-dithering technique is demonstrated. In the experiment, the master laser is split into two channels. Multi-dithering technique is used for phase control. One channel is modulated with a 100 kHz sine wave produced by signal generator, and DSP lock-in amplifier is used for electric signal processing in the feedback loop. When the phase control loop is off, the far field interference pattern is blurred and dynamic with 20% fringe contrast. When the feedback loop is closed, the far field interference pattern is clear and stable with 72% fringe contrast, and 75% coherent combination efficiency is achieved.

Interferometric testing and description of polarization ray tracing in multi-layer thin films

The production of thin films and their use in different industries necessitates the determination of their optical properties. This paper proposes an extended mathematical model of the output fringe field interference pattern. A general interference formula based on variable-incidence-angle polarizing interference microscopy has been derived for measurement of the optical properties of multi-layer thin film. In comparison with other well-known interferometric methods, the measurement accuracy of this new method is discussed. An example of applications to polypropylene sulfide (treated; coated on both sides with PVDC co-polymer) thin film is given.

The sensitivity of monitoring by measuring the frequency shifts of the sound field interference pattern

The sensitivity of the remote method of reconstructing the frequency spectrum of a water medium perturbation from the measured frequency shifts of the sound field interference peaks is investigated. On the basis of the Rayleigh criterion, an expression is derived for estimating the minimal frequency shift that allows the resolution of two neighboring peaks. The detection sensitivity for the sound velocity fluctuations caused by the time variability of the medium along the track is estimated. Results of computations for a perturbation in the form of background internal waves are presented.

Phase locking of three fiber lasers using an all-fiber coupling loop

An all-fiber coupling loop is constructed by three 2×2 fiber couplers according to certain rules, which connects three independent erbium-doped fiber lasers to form a coupled array. Thanks to the specially designed all-fiber coupling loop, the total loss of the phase locking array is reduced remarkably, and effective mutual injection coupling occurs between the component fiber lasers, so that the phase locking of the array is achieved. The far field interference patterns and output spectrum observed in experiment indicate that the array has achieved phase locking states. When the pump power of three component fiber lasers is 100mW each, the phase locking array gives 94mW stable coherent output.

Universal method to determine the thermo-optic coefficient of optical waveguide layer materials using a dual slab waveguide

A dual slab waveguide device method for determining the thermo-optic coefficient of waveguide layer materials is demonstrated. Temperature change-induced optical path length imbalance between two single slab waveguide modes provides the primary mechanism for detection. The waveguide mode output field phase change differences are encoded in shifts in the far field interference pattern. To illustrate the method, the thermo-optic coefficients of two In1−xGaxAsyP1−y quaternary alloys, 1.3Q and 1.15Q, are measured at a wavelength of 1.55μm and at a center temperature of 25.2°C. Their ratio is in excellent agreement with previous work, in accordance with optical dispersion models.

Ion sense of polarization of the electromagnetic wave field in the electron whistler frequency band

Abstract. It is shown that the left-hand (or ion-type) sense of polarization can appear in the field interference pattern of two plane electron whistler waves. Moreover, it is demonstrated that the ion-type polarized wave electric fields can be accompanied by the presence at the same observation point of electron-type polarized wave magnetic fields. The registration of ion-type polarized fields with frequencies between the highest ion gyrofrequency and the electron gyrofrequency in a cold, overdense plasma is a sufficient indication for the existence of an interference wave pattern, which can typically occur near artificial or natural reflecting magnetospheric plasma regions, inside waveguides (as in helicon discharges, for example), in fields resonantly emitted by beams of charged particles or, in principle, in some self-sustained, nonlinear wave field structures. A comparison with the conventional spectral matrix data processing approach is also presented in order to facilitate the calculations of the analyzed polarization parameters.Key words. Ionosphere (wave propagation) Radio science (waves in plasma) Space plasma physics (general or miscellaneous)

Determination of the Source Bearing in a Waveguide by Using the Sound Field Interference Pattern

Determination of the Source Bearing in a Waveguide by Using the Sound Field Interference Pattern

Determination of the Source Bearing in a Waveguide by Using the Sound Field Interference Pattern

The feasibility of determining the source bearing in a waveguide by an extended horizontal line array with the use of the sound field interference pattern is studied. The sound field is generated by an omnidirectional monochromatic point source and is represented as a sum of modes. The case of a small number of lowfrequency modes is considered.

Spectral intensity oscillations of a sound field in a randomly inhomogeneous ocean

The correlation description of the fluctuations of the frequency shifts, which occur in the sound field interference pattern of a shallow sea because of the spatial variability of the medium, is presented. The frequency shifts of the spectral intensity oscillations are estimated for a number of models of large-scale inhomogeneities. The possibilities for using this phenomenon for monitoring shallow-water ocean regions are discussed.

-Pulsed- Operation of -Cleaved-Facet- InGaN Laser -Diodes-

AbstractBlue-emitting nitride laser diodes have been fabricated on a-plane sapphire (1120). The active region is composed of 10 In.18Ga.82N quantum wells, which were grown by MOCVD at atmospheric and low pressure in a modified two-flow Thomas-Swan Ltd. horizontal reactor. The chemical precursors used were trimethylgallium (TMGa), trimethylindium (TMIn), trimethylaluminum (TMAI), ammonia, and disilane. The n- and p-contacts were formed by depositing Ti/Al/Ni/Au and Ni/Au/Ni/Au, respectively. Diode wafers were thinned to less than 50 μm before they were cleaved along the sapphire r-plane (1120).Lasers show TE polarization, spectral line narrowing, and far field interference patterns above the lasing threshold. The laser emission spectra peak at 410–420 nm. Under pulsed operation at room temperature, the lowest observed threshold current density was 15 kA/cm2 with threshold voltages ranging from 50–90 V. Differential efficiencies are as high as 7% with maximum output powers greater than 50 mW. Near and far field mode patterns are presented. Structures are gain-guided devices with each device occupying a mesa with a width of 125 μm. Device widths range from 3 to 20 μm, with lengths of 500 to 1200 μm.