Interference Structure Research Articles

High-order harmonic generation of ZnO crystals in chirped and static electric fields

High harmonic generation in ZnO crystals under chirped single-color field and static electric field are investigated by solving the semiconductor Bloch equation (SBE). It is found that when the chirp pulse is introduced, the interference structure becomes obvious while the harmonic cutoff is not extended. Furthermore, the harmonic efficiency is improved when the static electric field is included. These phenomena are demonstrated by the classical recollision model in real space affected by the waveform of laser field and inversion symmetry. Specifically, the electron motion in k-space shows that the change of waveform and the destruction of the symmetry of the laser field lead to the incomplete X-structure of the crystal-momentum-resolved (k-resolved) inter-band harmonic spectrum. Furthermore, a pre-acceleration process in the solid four-step model is confirmed.

Singular Points Location Pattern Analysis based on Modes Interference

<p>Given the lack of research on the regularity of distribution of singular points, the singular points under different influence factors are analyzed. The location of singular points for adjacent modes group (AMG) generated by the interference modes is derived using normal modes theory in the far field of the ideal shallow waveguide. The singular points are verified by simulation, which compares the distribution of the acoustic field and singular points. Moreover, it is concluded that the number and distribution of singular points in the period of the interference structure of the field (PISF) has a relationship with order (lower order of AMG) and adjacent order (difference between two orders of AMG). The arrangement of upper-lower-two-points increases by 2 with each increase of order and is distributed at both ends of PISF. The arrangement of rhombic-four-points increases by 1 with each increase of adjacent order and increases alternately at both ends of PISF. Meanwhile, there is a periodic relationship between the depth of the source and the location of singular points.</p> <p> </p>

Improved topography measurement with a high dynamic range using phase difference sensing technology.

Phase difference sensing technology (PDST) is employed for topography measurement, and two interference structures are proposed to achieve upper-limit adjustment and high resolution in the measurement range: a dual-wavelength system with a single Fabry-Perot (FP) cavity and a single-wavelength system with dual FP cavities. The phase difference between the two interference signals is determined by an elliptic fitting algorithm (EFA), and this change in phase difference is utilized to characterize the step height. Experimental results indicate that the measurement upper-limit can be adjusted to either 410 µm, 187 µm, or 108 µm by varying the wavelength difference in the dual-wavelength system, which gives a measurement error of 2.96%. In contrast, while offering a measurement resolution of 3.47 nm, the single-wavelength system exhibits a measurement error of 5.38%. The proposed method is capable of satisfying the measurement requirements during micro-electromechanical system (MEMS) processing with proficiency.

High-Resolution Laser Interference Ablation and Amorphization of Silicon.

The laser interference patterning of a silicon surface via UV femtosecond pulse irradiation, resulting in 350 nm periodic structures, is demonstrated. The structuring process was performed using a laser with a 450 fs pulse duration at a wavelength of 248 nm in combination with a mask projection setup. Depending on the laser fluence, single-pulse irradiation leads to amorphization, structure formation via lateral melt flow or the formation of voids via peculiar melt coalescence. Through multipulse irradiation, combined patterns of interference structures and laser-induced periodic surface structures (LIPSS) are observed.

Interference structures in photoelectron intensity distribution and closed orbit in the system

Interference structures in photoelectron intensity distribution and closed orbit in the system

Pseudo-resonance phenomenon of valveless piezoelectric pump

Volumetric piezoelectric pumps are widely used in the field of microfluidic drive due to their simple structure, flexible design, and absence of magnetic interference. As driven by the volume change of the pump chamber, the majority of this kind of pumps work under the first order resonance frequency, where the volume change is the largest. However, the experimental parts or data of many studies reflect a phenomenon that a flow rate peak exists in the non-resonance frequency range. This phenomenon has not been studied or explained in depth, and goes against conventional vibration theories. In this study, we define this phenomenon as the pseudo-resonance phenomenon, and the corresponding flow rate peak is named as the pseudo-resonance flow rate peak. First, a non-single-channel composite tapered tube valveless piezoelectric pump (NCTVP) was designed, which reproduced the pseudo-resonance phenomenon reported in the literature. Through displacement measurement experiments, it was demonstrated that the vibration mode of the piezoelectric vibrator was B00 mode when the pseudo-resonance phenomenon occurred. Then, frequency sweeping experiments and flow field observation experiments were conducted, it can be obtained that the pseudo-resonance phenomenon is caused by the reaction force of the water to the piezoelectric vibrator, and the reaction force is generated by the impact of two streams. Finally, based on the experiment results, a theoretical model was established; it was deduced that the first order resonance flow rate peak was caused by the flow resistance difference between the forward and reverse flows of the tapered tubes in NCTVP, and that the pseudo-resonance flow rate peak was caused by the water hammer effect. By applying the pseudo-resonance phenomenon, another flow rate peak was obtained in the non-resonance frequency range without changing the mechanical structure, which can enable piezoelectric micro nano pump to obtain extra flow rate or pressure without changing the constraint boundary conditions.

Temperature compensated magnetic field sensor based on magnetic fluid infiltrated cascaded structure of micro-tapered long-period fiber grating and fiber Bragg grating

Magnetic fluid (MF) infiltrated fiber-optic interference structures can be used to realize miniature magnetic field sensor for various applications needing sensitive magnetic field measurement, however, these sensors are typically also sensitive to temperature variations. To solve the problem of temperature cross sensitivity, an MF-infiltrated micro-tapered long-period fiber grating (MT-LPFG) and a femtosecond laser inscribed fiber Bragg grating (fsFBG) cascaded sensing structure is proposed and demonstrated. The MT-LPFG is fabricated by a fused tapering method under the illumination of a CO2 laser and is inserted into a glass capillary infiltrated with MF for magnetic field measurement, and the fsFBG is cascaded to the MT-LPFG for temperature measurement. Through the simultaneous monitoring of the resonant wavelength shift of the MT-LPFG and the Bragg wavelength shift of the fsFBG, temperature and magnetic field strength can be simultaneously extracted through a sensitivity coefficient matrix. As a result, the influence of the temperature on the MF-infiltrated MT-LPFG can be effectively compensated. Experimental results show that a magnetic field strength sensitivity of 21.86 pm/Oe can be achieved in a magnetic field strength range of 10-80 Oe and a temperature range of 30-60℃.

Arbitrary-ratio 1 × 2 optical power splitter based on thin-film lithium niobate.

Optical power splitters (OPSs) have been widely used in photonic integrated circuits, but an OPS with a large fabrication tolerance and free choice of power splitting ratio (PSR) is still highly desired for thin-film lithium niobate (TFLN) platform. Here, we propose and experimentally demonstrate several 1 × 2 OPSs with PSRs from 50:50 to 5:95 using TFLN platform. The proposed devices are built by multimode interference structure to achieve a broad bandwidth and large fabrication tolerance. Various PSRs can be obtained by adjusting the geometry structure of the multimode interference region. All of our fabricated devices feature an insertion loss lower than 0.3 dB at the wavelength of 1550 nm, and a PSR variation less than 3% in the range of 1520 nm to 1590 nm.

Identifying potential inhibitors of C-X-C motif chemokine ligand10 against vitiligo: structure-based virtual screening, molecular dynamics simulation, and principal component analysis

The research aims to envisage small molecule inhibitors targeting the C-X-C motif chemokine ligand 10 (CXCL10) of the JAK/STAT pathway. CXCL10 plays a significant role in inducing auto-immunity in vitiligo through JAK/STAT pathway. To accomplish the aim, structure-based virtual screening with fundamental search limits, e.g., molecular weight (MW ≤ 500 Da), hydrogen bond donor (HBD ≤ 5), hydrogen bond acceptor (HBA ≤ 10), and lipophilicity (logP ≤ 5) was used to screen investigational molecules from MCULE database. The SBVS-ligand hits were sifted through toxicity profiling followed by filtration through the Brain or IntestinaL EstimateD-Egg model to check the human intestinal abortion and blood-brain barrier permeation based on two physicochemical properties, including topological surface area and WLOGP. The BOILED-Egg filtered compounds were passed through drug-likeness features other than Pfizer’s Lipinski rule of five, viz., Ghose filters, Muegge filters, Egan parameters, and Veber filters, followed by medicinal chemistry’s pan assay interference structure and Brenk alert investigation. Chemical compounds that comply with the above ADME descriptors were docked with target protein CXCL10 via AutoDock Vina. The stability of the top two ligand hits was assessed through dynamics simulations of 100 ns and principal component analysis and compared with the reference drugs Baicalein and EGCG. Based on the findings of Gibbs free energy of binding, ADME profiling, medicinal chemistry attributes depiction, root-mean-square deviation, root-mean-square fluctuation, solvent accessible surface area, the free energy of solvation, the radius of gyration, and PCA, MCULE2726078782-0-2 was found better than potential reference drug Baicalein. Communicated by Ramaswamy H. Sarma

Strong-Field Ionization of Hydrogen Atoms with Quantum Light.

We study the strong-field ionization driven by quantum lights. Developing a quantum-optical-corrected strong-field approximation model, we simulate the photoelectron momentum distribution with squeezed-state light, which manifests as notably different interference structures from that with coherent-state (classical) light. With the saddle-point method, we analyze the electron dynamics and reveal that the photon statistics of squeezed-state light fields endows the tunneling electron wave packets with a time-varying phase uncertainty and modulates the photoelectron intracycle and intercycle interferences. Moreover, it is found the fluctuation of quantum light imprints significant influence on the propagation of tunneling electron wave packets, in which the ionization probability of electrons is considerably modified in time domain.

A plastic optic fiber sensor with temperature compensation for refractive index measurement

An optical fiber sensor based on a gradually hot-pressed flatted plastic optical fiber (POF) and F-P interference structure is proposed to eliminate the effect of ambient temperature drift in the refractive index (RI) detection of glucose concentration. Based on the analysis of the influence of the sensor itself and the RI change of solution on the transmitted light intensity under the effect of temperature, a self-calibration formula was established by means of the peak wavelength and the transmitted light intensity of interference peak were used as information carriers to calibrate the parameters. The results of the validation show that the temperature drift compensation method proposed in this paper is feasible. The maximum relative error between the measured RI after compensation and actual value is only 0.032%, and it has good repeatability. The precision to the RI with temperature compensation of the gradually hot-pressed flatted POF and F-P interference structure has potential applications in the biochemistry, medical diagnosis, and environmental monitoring.

Voltage and frequency stabilization by fuzzy integrated droop control of a multi renewable source micro grid

A multi renewable source micro-grid system has many power quality issues when it is operated in grid islanding condition. During grid connected mode the voltage and frequency of the system will remain stable for small disturbances like load changes or environmental changes. During these sudden variations in the system, the grid supports the load maintaining the system stable. In this paper a droop control is introduced for the renewable source module 3-ph inverter during standalone mode supporting the load. For detection of grid islanding, an active islanding detection control is adopted which makes the 3-ph inverter to shift from synchronous reference frame (SRF) control to droop control. The performance of the droop control is improvised with fuzzy interference structure (FIS) module replacing the conventional proportional integral and derivative (PID) control. A comparative analysis is done in this paper with different controllers in droop control scheme using matrix laboratory (MATLAB) Simulink software. Stability analysis is carried out on the system determining the voltage and frequency fluctuations during grid disturbances. There is an improvement in load compensation, voltage ripple, voltage magnitude, frequency ripple and settling time with the introduced fuzzy droop controller.

Numerical investigation on Coulomb impact on bouquetlike photoelectron momentum distributions

Deploying the strong-field approximation and the saddle point methods, we numerically simulate the Coulomb impact on the bouquetlike photoelectron momentum distributions (PMDs) induced by intense laser ionization of hydrogen atom. The bouquet-like PMDs, also dubbed as electron carpet-like PMDs, are interference structures perpendicular to laser polarization in PMDs. The results show that the bouquetlike interference PMDs are mostly altered for small momenta, for both the above-threshold ionization (ATI) and intra-cycle interference (ICI) fringes, compared with the Coulomb-free situation. We propose a correlation parameter (CP) to quantitatively elucidate the PMDs alterations due to Coulomb effect. Also, we formulate an expression for successfully tracing out the ATI and ICI fringes, which proves that the bouquetlike PMDs alterations are attributed to an extra action phase due to Coulomb interaction.

Nondipole signatures in ionization and high-order harmonic generation

We analyze nondipole effects arising in ionization and high-order harmonic generation for a two-dimensional hydrogen atom irradiated with either low- or high-frequency laser pulses. In the low-frequency case, the electron wave packet dynamics is dominated by rescattering processes within the laser pulse. Here both odd- and even-order harmonics are generated in the direction of the laser field propagation and polarization, respectively. For high-frequency pulses, such rescattering processes can be neglected. We demonstrate that a significant portion of photoelectrons is detected opposite to the laser pulse propagation direction as a consequence of their postpulse wave packet spreading and interaction with the parent ion. This is accompanied by rich interference structures formed in the momentum distributions of photoelectrons. Our results follow from the numerical solution of the time-dependent Schr\"odinger equation, which is based on the Suzuki-Trotter scheme with the split-step Fourier approach. The method relies on a Hamiltonian decomposition, where except for the components depending exclusively on the momentum or on the position operators, there are also terms depending on both momentum and position operators in particular configurations. We demonstrate that, as long as the latter does not depend on noncommuting coordinates of the momentum and position operators, nondipole effects in laser-matter interactions can be studied without applying extra approximations and unitary operations.

Numerical Investigation of on-Chip Multi-Gas Sensing Using a Low-Repetition-Frequency Microcavity Kerr Comb With Backward Interference Structure

By integrating a microcavity Kerr frequency comb with an interferometric arm structure for backward coupling with a slot sensing waveguide, we present a new on-chip multi-gas sensing device. The microcavity used for frequency comb generation has a novel symmetric double-ring structure with a large roundtrip length, which makes it possible to obtain high-resolution frequency-resolved absorption spectra. In the meanwhile, a flat octave-spanning broadband spectrum is obtained by dispersion engineering of the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> -based micro-rings with a horizontal single slot structure. Without the use of an additional gas cell, the large-length sensing waveguide allows for improved integration. A multiple soliton comb with high pump-to-frequency comb conversion efficiency under the optimization of the microcavity structure to improve pump depletion was obtained. The simulation shows its high stability and application feasibility, and the sensing performance of several gas species in different wavelength regions is verified and analyzed.

Classification of inbound and outbound ships using convolutional neural networks

In general, a single scalar hydrophone cannot determine the orientation of an underwater acoustic target. However, through a study of sea trial experimental data, the authors found that the sound field interference structures of inbound and outbound ships differ owing to changes in the topography of the shallow continental shelf. Based on this difference, four different convolutional neural networks (CNNs), AlexNet, visual geometry group, residual network (ResNet), and dense convolutional network (DenseNet), are trained to classify inbound and outbound ships using only a single scalar hydrophone. Two datasets, a simulation and a sea trial, are used in the CNNs. Each dataset is divided into a training set and a test set according to the proportion of 40% to 60%. The simulation dataset is generated using underwater acoustic propagation software, with surface ships of different parameters (tonnage, speed, draft) modeled as various acoustic sources. The experimental dataset is obtained using submersible buoys placed near Qingdao Port, including 321 target ships. The ships in the dataset are labeled inbound or outbound using ship automatic identification system data. The results showed that the accuracy of the four CNNs based on the sea trial dataset in judging vessels’ inbound and outbound situations is above 90%, among which the accuracy of DenseNet is as high as 99.2%. This study also explains the physical principle of classifying inbound and outbound ships by analyzing the low-frequency analysis and recording diagram of the broadband noise radiated by the ships. This method can monitor ships entering and leaving ports illegally and with abnormal courses in specific sea areas.

Optical fiber pH sensor based on a multimode interference device with polymer overlay.

An optical fiber pH sensor based on a multimode interference structure is presented. The sensitive element is a piece of no-core fiber (NCF) coated with a mixture of polyallylamine hydrochloride and polyacrylic acid by a modified layer-by-layer (LbL) self-assembly method. It is experimentally shown that by reducing the diameter of the NCF by chemical etching, the sensitivity is increased from -0.31n m/p H to -2n m/p H. The sensor exhibits a high linear response of 0.997 over a pH range from 5 to 11.3 with a rapid response time lower than 1s.

Statistical spatial properties of a light field on a target plane

Studying the light field characteristics of a target plane is critical in controlling the laser-plasma instability (LPI), which is necessary to increase laser energy utilization and compression symmetry in high-power laser facilities. In this study, a statistical method is used to analyze the transmission light characteristics of a target plane for single and multiple beams. We reconstructed the light transmission model on the target plane and analyzed the relationships between the focal spot width and incidence angle, and speckle width and incidence angle using the autocorrelation function. In addition, the relationship between the interference pattern and incident beams is obtained by deriving the beam superposition theory. The results show that the speckle and focal spot widths are stretched in the direction in which the incident plane projects. The direction of the interference structure generated by multiple-laser beams is perpendicular to the line joining of the sub-beams, and the period is related to both wavelength and incidence angle. Experimental results are consistent with the theoretical analysis. The influence of incident beam number on the focal spot uniformity is also studied. The results are of great significance for regulating the sub-beam incidence direction, understanding light properties to further improve focal spot uniformity and suppress the LPI.

High sensitivity mercury ion fiber optic sensor based on Mach–Zehnder interference

This paper proposes a novel optical fiber sensor for highly sensitive Hg2+ detection based on Mach–Zehnder interference (MZI) structure and thiophene–chitosan hydrogel (TCH). We obtained the MZI structure by splicing the coreless fiber (CLF), thin core fiber, and CLF. And then, we etched the thin-core optical fiber cladding and assembled the TCH to produce a Hg2+ sensitive sensor. According to theoretical derivation and experimental verification, the detection sensitivity of the sensor to Hg2+ can reach 1.008 × 1011 mol l−1, and the detection limit is 5 × 10−13 mol l−1. The sensor also has performance stability within 24 h for concentration measurement, with an average standard deviation of 3.2 × 10−13 mol l−1 within an hour of observation. In addition, the sensor has the advantages of specificity, simple preparation, and low cost, and it is suitable for monitoring the concentration of Hg2+ in complex water systems.

High-resolution passive depth estimation for broadband sources in deep water based on orthogonal matching pursuit algorithm

The propagation mode of reliable acoustic path (RAP) in deep water is widely used in the field of target detection. A receiver set at the bottom of the seabed can receive acoustic signals from RAP. The direct (D) wave and the surface-reflected (SR) wave from a broadband source form an undulating interference structure in the frequency domain. This feature is sensitive to target depth and is thus used for depth estimation. Traditionally, depth estimation using the interference pattern, the scalar intensity in the frequency domain is processed by the optimal Fourier transform to extract the line spectrum in the depth domain. Based on this method, we proposed a passive depth estimation method for underwater broadband sources in deep water based on the orthogonal matching pursuit (OMP) algorithm. The OMP-based method is applied to scalar vertical line array (VLA) and single vector sensor (SVS) data. The OMP-based method largely eliminates side lobe interference, reduces the width of the main lobe, and improves depth estimation resolution while ensuring the stability and reliability of the results. Finally, the experimental data of VLA and SVS in the South China Sea are processed to validate the proposed method.