This paper presents numerical results on the spiderlike photoelectron momentum distributions (PMDs) induced by the ionization of hydrogen atoms by an intense laser pulse. In addition, although the standard semiclassical rescattering model (SRM) has simplified actions of electrons, it fails to take complex Coulomb interaction into account. Different from existing numerical correction, this paper carries out an analytical approximate treatment of Coulomb interaction during the ionization, introduces it into SRM, and successfully constructs an analytically-Coulomb-corrected SRM (AC-SRM). Based on AC-SRM, the systematic shifts of interference patterns caused by spiderlike PMDs and Coulomb interaction are simulated and calculated. Furthermore, through the classical phase, time-dependent Schr?dinger equation (TDSE), electron orbit, and other methods, this paper quantitatively analyzes the shifts and explores the corresponding mechanism. The results show that the proposed classical phase method is the most sensitive to the Coulomb interaction in the spiderlike PMDs, especially to the first interference minima, and the accurate TDSE values verify the correctness of simulated results obtained by AC-SRM.

Nonsequential double ionization (NSDI) of N2 molecules in counter-rotating two-color circularly polarized few-cycle laser fields is investigated by the classical ensemble method. The results show that for the determined laser intensity, the yield of NSDI decreases significantly with the increasing laser wavelength, which is caused by the diffusion effects of electron wave packets. It is also found that the ionization mechanism of NSDI is affected by the laser wavelength. Collision excitation ionization becomes increasingly dominant with the rising laser wavelength, which is related to the return trajectory and return energy of the first electron. At the same time, the electron momentum distribution of NSDI is discussed in this paper. The electron momentum distribution varies significantly with the laser wavelength, and the longer laser wavelength leads to clearer "rotating three-lobed fan-like" structures.

Phase grating (PG) mark is a key component of a micro-displacement measurement system. In this paper, a design method of PG mark in resonance domain combining rigorous coupled wave analysis (RCWA) method with differential evolution algorithm is proposed to address issues including insufficient calculation accuracy of scalar diffraction theory and time consuming of parameter traversal design method. Firstly, according to the self-reference interference displacement measurement model, the maximum sum of measured optical signal-to-noise ratio (SNR) is regarded as the evaluation function of grating mark design. The relationship between the number of spatial harmonics and calculation accuracy in RCWA method is studied under different incident light wavelengths, polarization states, and grating periods. In view of the measurement requirement of multi-wavelength illumination micro-displacement, the proposed method is used to design the mark, and it is compared with conventional design methods. The results show that for the PG with period of 3.2 μm, the duty cycle of the grating is 0.484, and the groove depth is 161.5 nm under transverse magnetic (TM) light. Furthermore, the sum of SNR reaches the maximum value of 586.63. Compared with conventional design methods, the proposed method shortens the time in designing the PG mark to 0.2%, and the maximum improvement ratio of the sum of SNR reaches 24.4%.

Diffracted wavefront aberration and distribution of far-field diffraction light are important manifestation for the quality of pulse compression gratings with a large aperture. In order to optimize the energy distribution of far-field light spots of splicing gratings, this paper proposes a parallel splicing method for gratings. Grating parallel splicing and grating aligned splicing are simulated under different aberrations, and the energy distribution of far-field diffraction light spots of the corresponding wavefront is calculated. The statistical results show that the peak valley (PV) value of the wavefront of gratings with parallel splicing is smaller than the that of gratings with aligned splicing. However, the energy distribution of the far-field scattering light spots of gratings is related to the type of aberrations and the modes of splicing. Experiments are carried out on gratings with holographic exposure splicing, and the results show that grating parallel splicing method can not only reduce the PV value of the -1st order diffracted wavefront aberration, but also improve the energy concentration of far-field diffraction light spots. Therefore, it provides a new method for holographic splicing gratings.

In order to control the linear polarization (LP) mode in few-mode erbium-doped fiber amplifiers (FM-EDFAs), the dependence of mode field distribution and effective refractive index in optical fibers with elliptical cores on the elliptical parameter (the ratio of the major to minor axis length of the elliptical core) is investigated by multi-physics field simulation software. When the elliptical parameter is more than 1.050, TM01 and HE21o, as well as TE01 and HE21e can be expressed by LP11 odd and even modes which have an effective refractive index difference of larger than 10-4, with negligible mode crosstalk. This paper approximately constructs the mode field in an optical fiber with an elliptical core through the superposition of the LP modes, and compares the gain errors calculated by the approximate LP mode field and the precise mode field in the active fiber with an elliptical core. When the elliptical parameter is less than 1.250, the three-mode gain error calculated by the approximate LP mode field is smaller than 0.5 dB. The results show that the approximate LP mode field can greatly reduce the design complexity of FM-EDFAs with elliptical cores during analysis.

A central refractive index depressed few-mode erbium-doped fiber (FM-EDF) can change the number and cut-off order of transmission modes, and has an excellent performance in terms of mode field modulation and gain equalization. In this paper, the equivalent refractive index theory is employed to describe the cut-off characteristics of optical fiber modes, and the changes of modes during the transition from the traditional step-index fibers to ring-core fibers are studied. The results show that when the central depression is larger than 0.012, the optical fiber only supports LPn1 mode transmission and makes the field energy of LP01 mode shift away from the central areas. Additionally, when the optical fiber is used in signal amplification areas, and there is a corresponding linear relationship between the refractive index depression and the radius of the doped region, the differential modal gain can be kept below 2 dB. A homemade central depressed FM-EDF is used to test the gain characteristics of LPn1 mode. The experimental results show that the gain of all signal modes is higher than 18 dB, and the differential modal gain is 1.3 dB.

It is necessary to detect and calibrate the device parameters to reduce errors caused by device parameter deviation during the polarization information extraction of the target. In this paper, the parameters of the Savart prism are calibrated through the beam-splitting imaging experiment on the Savart prism. In addition, a simulation is carried out on the basis of the fractional amplitude polarization camera, and the demodulation effect is quantitatively analyzed by the calculation of the structural similarity and the least square fitting method. Finally, the demodulation diagrams under different polarization states are compared by polarization imaging experiments. The influence of parameter errors on different Stokes components is analyzed, and the effectiveness of the parameter calibration method is verified.

In the application of a rotating vision measurement system composed of a turntable and a camera, it is important to accurately calibrate the distance between the optical center of camera and the rotation axis, so as to facilitate subsequent data splicing. Therefore, a method for calibrating the distance between the optical center of camera and the rotation axis based on the principle of binocular vision is proposed, and the corresponding mathematical model is established, with the analytical expression deduced. The turntable drives the camera with known internal parameters to rotate once, and two target images are shot. Then, the distance between the optical center of camera and the rotation axis can be calculated according to the image coordinates of the feature points on the target images, their corresponding spatial distance, the rotation angle, and the internal parameters of the camera. As a result, computer simulations and experiments verify the effectiveness of the proposed method, and the calculation results can be used to align the optical center of camera with the rotation axis in the rotating vision measurement system, with an alignment accuracy of 0.16 mm.

When a polarized camera is used to realize instantaneous phase-shifting and obtain photoelastic fringes, quantitative error and compensation analysis is often ignored. The error of the instantaneous photoelastic phase-shifting method in a circularly polarized field is primarily caused by a mismatch between the wavelength of the quarter-wave plate and the light source. Based on the Stokes vector and Mueller matrix, this paper theoretically derives the error and compensation equations of the photoelastic properties, and discusses the error distribution of the stress direction angle and phase retardation of samples. The results show that the isochromatic fringe error is directly proportional to the mismatch value. In addition, the isoclinic fringe error is nonlinear, but it is in direct proportion to the cosine of the mismatch value and inverse proportion to the difference between two light intensities. Furthermore, the paper analyzes the influence of the spectral width of the light source on the compensation effect, and finds that the spectral width is directly proportional to the wavelength and inversely proportional to the mismatch error. Finally, the correctness of the error analysis and compensation method is verified through the simulations and experiments of the diameter-stressed disk, and the isoclinic separation in the stress direction is discussed.

High harmonic generation (HHG) with tunable spectral characteristics by intense laser-plasma interaction has long been a research hotspot both in China and abroad. In this study, a two-dimensional particle simulation program is employed to investigate the radiation characteristics of the HHG by the plasma waveguide driven by an ultra-short ultra-intense laser pulse and the related dynamic behavior of the electrons. The influences and regulation laws of key parameters, including driving laser intensity and plasma density, on the conversion efficiency and ellipticity of the HHG are discussed, and their underlying physical mechanisms are analyzed by the Baeve-Gordienko-Pukhov (BGP) theory. This study provides a novel technical route for developing high-brightness, ultra-short ultra-fast, and circularly polarized mesa-type radiation sources in the wavelength range from deep ultraviolet to soft X-ray and is thus expected to further facilitate the development of ultrafast ultra-high-sensitivity techniques for chirality detection.

In vortex lasers, two modes with the same order but opposite chirality will be superposed in output. Therefore, we build a partially coherent superposition model for the two modes with opposite chirality and the same order, and investigate the superposition characteristics of the modes under continuous and passively Q-switched operation separately through experiments. Under a low-power pump, the modes coherently superpose to form petal-like light spots with the orientation determined by the initial phase difference under continuous operation. However, under Q-switched operation, the orientation of the petal-like light spots changes randomly with the pulse train. Under a high-power pump, the two modes superpose incoherently and present ring-shaped light spots without vortex phases, which is due to the random phase fluctuation caused by fierce mode competition. The mode chirality can be controlled by the tilted output mirror and the passive Q-switch to generate continuous vortex beams for the LG0,±1 modes, LG0,±2 modes, and LG0,±3 modes with the power of 0.88 W, 0.85 W, and 0.79 W, respectively, and LG0,±1 pulse vortex beam with a repetition rate of 12.6 kHz, a pulse width of 28.6 ns, and a peak power of 1.33 kW.

For the traditional large field-of-view (FOV) off-axis reflective optical system, the initial configuration solves only axial aberrations, while the off-axis image quality is poor, and it is difficult to optimize large FOV image quality. Considering the above problems, this paper establishes an initial configuration solution method with joint aberrations of Nodal aberrations and Seidel aberrations. A global simulated annealing algorithm is used to automatically obtain thesolution of the large FOV off-axis reflective initial configuration. As a result, the "positive-negative-positive" initial configuration of the large FOV off-axis three-mirror system is obtained directly, with good image quality in the on-axis and off-axis FOV. Finally, a compact freeform surface optical system with a large FOV of 30°×3° is designed on the basis of this initial configuration, which has a focal length of 500 mm and an F-number of 5. The optical system has good imaging quality, no eccentricity or tilt, and easy assembly and alignment, which can provide a reference for the design of the wide-format push-broom imaging space optical cameras.

Nematic liquid crystals (NLCs) have been widely used in the display industry and other electrooptical fields due to their unique optical and electrical anisotropies. The continuous development of optical communication requires faster electro-optic responses of liquid crystal materials. Here, we systematically explore the electrical modification of the orientation fluctuations and the uniaxial order parameter in six negative NLCs by applying electric fields perpendicular to the average molecular orientation and using a special incidence of light. Experimental results show that the switching-on time and switching-off time of the electro-optic responses are smaller than 350 ns. The field-induced birefringence change rate of NLCs grows as the dielectric anisotropy increases. The maximum field-induced birefringence change rate is proportional to both the applied electric field and the nematic dielectric anisotropy.

A sub-terahertz on-chip transmission line based on spoof surface plasmon polaritons (SSPPs) is proposed, and its structure is designed and processed by InP technology. In order to reduce the area occupied by the SSPPs structure with the conventional rectangular grooves, a folded SSPPs structure is proposed. With the same asymptotic frequency, the area occupied by the proposed structure is reduced by 57.2%. In addition, the efficient excitation of the folded SSPPs transmission line is realized by the grounded coplanar waveguide (GCPW) and a gradient transition structure. The SSPPs transmission line is measured by a terahertz on-chip test system. Test results show that the insertion loss of the SSPPs transmission line is less than 3 dB/mm with the frequency band ranging from 110 to 170 GHz, and the return loss is better than 12.5 dB, which is in good agreement with the simulated ones.

In this paper, polarization intensity as a function of crystallographic orientation is studied by the InGaN/GaN single quantum well model. The results reveal that the polarization electric field inversion in the semi-polar (101¯1) quantum well leads to upward bending of the energy band, and the electron wave function in the quantum well is close to the n-side, which is likely to successfully suppress electron leakage. The simulation of the epitaxial structure of (101¯1)-plane InGaN/GaN multi-quantum-well blue light-emitting diodes (LEDs) demonstrates that LEDs grown on the semi-polar (101¯1) plane can elevate the effective blocking barrier of the quantum barrier and suppress electron leakage. Moreover, the (101¯1) plane greatly reduces the hole injection barrier, promotes the even distribution of carriers, and reduces Auger recombination probability. Finally, the efficiency droop in (101¯1)-plane GaN-based LEDs is drastically reduced to 9% at the current density of 300 A/cm2 compared with 42% efficiency droop in the (0001) plane, and electroluminescence intensity is increased by 48%. The electrostatic field inversion of the (101¯1)-plane InGaN quantum well is an important reason for its excellent photoelectric properties.

Goos-H?nchen (GH) shift refers to the lateral shift of reflected light center in two-dimensional or higher-dimensional systems. Based on the Mie theory, this paper utilizes the Drude model of metal nanoparticles to study the change laws of the lateral shift of nanoparticles in the far field under the illumination of linearly polarized light. In addition, the paper derives an analytical expression for the GH shift and uses a simplified model to unveil the underlying mechanism of GH shift inversion. It is found that when the electric dipole couples with the electric quadrupole, GH shift reaches two peaks different from that in other wavebands at Fano resonance area. The finding lays a foundation for the development of supersensitive sensors based on GH shift.

Deterministic interface states in photonic crystals have attracted extensive attention from researchers in recent years due to their widespread applications in optical waveguides and other fields. This paper uses effective electromagnetic parameters to predict the existence of deterministic interface states in photonic crystals, which extends the Zak phase theory of band structures. The effective electromagnetic parameters are superior because they bring advantages of requiring no calculation of complex band structures and Zak phase and making the design of deterministic interface states in photonic crystals more convenient. Similar to surface plasmon polaritons, deterministic interface states can exist when the sum of the impedances of two photonic crystals forming the interface is zero. Therefore, the existence of deterministic interface states in anisotropic photonic crystals only depends on the effective dielectric constant and effective permeability in specific directions. In addition, it is found that deterministic interface states can exist and propagate only along specific interface directions by designing anisotropic photonic crystals with required effective electromagnetic parameters. The simulation results verify the accuracy of the effective medium theory for photonic crystals and the existence of interfacial states.

This paper focuses on a kind of metal cylinder, which has artificial microstructures of periodic subwavelength grooves on the surface, works in the terahertz band, and has been studied extensively. Losses are introduced into some of the grooves to examine the influence of the material loss on the scattering properties of metal microstructure cylinders. The results reveal that at a specific frequency, the absorption cross-section of the overall metal microstructure cylinder remains almost zero regardless of how the loss changes. The analysis of scattered field distributions and eigenmodes demonstrates that this loss-independent anomalous scattering is due to the loss-free bound state of the microstructure caused by symmetry breaking. The electric fields of this bound state are mainly distributed in the loss-free grooves, whereas almost no electric field is observed in the lossy grooves. This study provides a new method for designing high-performance photonic devices based on lossy metal microstructure cylinders.

Here, we begin with analyzing the principle of phase modulation mechanism of metasurface, and then discuss how to utilize multiple degrees of freedom to achieve multifunctional optical response. For a proof of concept, we design several metasurfaces composed of amorphous silicon (a-Si) nanorods to demonstrate the multichannel control of light with different phase mechanisms. This study provides theoretical support for flexible design of metasurfaces, and introduces and gives a summary of the research progress of multifunctional meta-devices.

On the basis of the electromagnetically induced transparency (EIT) phenomenon which occurs in three-level Λ-type coherent media modulated by rectangular barriers, a theoretical scheme is proposed to achieve an all-optical switch at a weak light level. The Maxwell-Bloch equations are derived to describe the dynamic evolution of optical pulses in the system under the semi-classical framework. By the multi-scale method, the nonlinear Schr?dinger equation (NLSE) describing the propagation of optical pulses under the modulation of rectangular barriers is obtained. In different incident cases, such as single optical soliton incidence, as well as symmetric and asymmetric double optical soliton incidence, this study systematically investigates the excitation properties of propagation modes and cut-off modes in the rectangular barrier. Moreover, it analyzes the influence of the phase of incident double optical solitons and the intensity and width of rectangular barriers on the propagation properties of different modes in rectangular barriers. Finally, this paper proposes an all-optical switch at a weak light level by changing the characteristic parameters of rectangular barriers and the phase of the incident optical pulses.

The two-photon absorption in a two-atom cavity quantum electrodynamics (QED) system is studied in detail. In free space, two atoms of different frequencies cannot be excited at the same time because of the quantum interference effect. In the strongly coupled cavity QED system, however, the coupling between the atom and the cavity field leads to new transition channels, which makes diatomic excitation possible. The photon excitation spectrum of a two-atom cavity QED system is elaborately studied by the master equation of numerical simulation and is compared with the two-photon excitation spectrum, which proves the possibility of two-photon excitation. Further analysis of the second-order correlation function and the diatomic excitation probability of the photon reveals the statistical properties of the photon in the cavity and the physical mechanism of diatomic excitation.

This paper investigates the single-photon scattering properties in a chirally-coupled system of a three-level V-type giant atom with a pair of waveguides. The two transitions of the three-level V-type system are chirally coupled with the two waveguides separately, and the two excited states are coupled by a classical light field. Then, the single-photon scattering amplitude is obtained by the real-space Hamiltonian method. The results reveal that one can realize the nonreciprocal single-photon frequency convertor and beam splitter with the efficiency of 1 under ideal conditions by the manipulation of the classical light field. The single-photon scattering properties depend on the accumulated phase by the photon propagation between the two coupling points of the giant atom and the waveguides. By controlling the phase, one can realize a single-photon frequency convertor and beam splitter with high frequency sensitivity to the incident light.

The photon correlation properties of coherently driven atoms strongly coupled with a single-mode cavity and the influence of collective effect on the mean photon number and photon correlation properties in asymmetric coupling are studied in this paper. Under weak pump field excitation, the driven atom can realize the single photon blockade effect, and the overflow photons from the cavity follow the sub-Poisson statistics, showing the anti-bunching state. Additionally, the distance between two atoms affects the dressed energy level. When the couping phase difference of two atoms is greater than 90°, the asymmetric coupling results in strong photon excitation at the central frequency. Due to the resonance effect, the intra-cavity photons exhibit strong bunching behavior. As the intensity of the driving field increases, the number of photons at both sides of the edge gradually rises and the two-photon excitation becomes dominant, which can realize the two-photon blockade, namely that photons appear in pairs. The present system provides a good platform for studying quantum optical phenomena due to collective effects.

In this study, the electromagnetically induced transparency (EIT) of Pr3+∶Y2SiO5 doped photonic crystals in free space and confined systems of sandwich waveguides is theoretically investigated, and the influence of the confinement effect on EIT is revealed. Specifically, the influence of inhomogeneous broadening on the EIT of doped photonic crystals is thoroughly examined according to the semi-classical theory of light-matter interaction, and the conditions for the generation of EIT are obtained analytically. The validity of the theory is confirmed by comparison with experimental results. In addition, the EIT in a Pr3+∶Y2SiO5 doped photonic crystal sandwich waveguide system is further explored. The influence of the local electric field confinement effect on EIT is analyzed, and the conditions for the achievement of EIT in such a sandwich waveguide system are obtained in an analytical manner.

For the honeycomb-lattice photonic crystals made of perfect electric conductor cylinders, a mathematical model is proposed to calculate the inter- and intra-lattice coupling intensity by analogy with electrostatic interactions. The comparison of inter- and intra-lattice coupling is made to explain the quantum spin Hall effect at the structure level. The calculated results reveal that the intra- and inter-lattice coupling intensity changes with the increase in the cylinder radius, namely that a topological phase transition occurs. Numerical simulations confirm that topological inversion of the band structures of photonic crystals on both sides of the transition position occurs, and a unidirectional topological photonic waveguide emerges at the interfaces between these photonic crystals of different topological phases. The proposed mathematical model can predict the topological phase transition of optical/acoustic topological insulators and can provide a reference for subsequent component development.

Taking the Haldane model as the research system, we extend the current study of topoelectrical circuits modulating interactions and design and construct a general method to modulate the on-site potential energy of the tight-binding model. In this method, efforts are made to achieve the interface state modulation, including changes in the on-site potential energy of the Haldane model, which involves the change in overall on-site potential energy, the application of different on-site potential energies on the two atoms of the honeycomb lattice, and the adjustment to the on-site potential energy of boundary atoms, and in particular, the development of the corresponding design scheme for circuit experiments. The method provides a new idea for further control and utilization of interface states.

The development and application of transformation optics provide a new approach to on-chip integrated multi-frequency transmission and the design of broadband nonlinear photonic devices. In this paper, a model based on the transformation optics theory is utilized to obtain a waveguide device featuring on-chip rainbow trapping by manipulating the spatial distribution of dispersion and group velocity of thin-film lithium niobate photonic crystals. The analysis of the nonlinear four-wave mixing process reveals the bright application prospect of the proposed waveguide device in broadband four-wave mixing. The transformation optical waveguide structure designed can also be applied to other nonlinear integrated optical devices.

A droplet-type optical fiber volatile organic compound (VOC) sensor based on polydimethylsiloxane (PDMS) is proposed to detect the leakage of VOCs. The droplet-type sensor is formed from a standard single-mode optical fiber that is bent and encapsulated in PDMS. In the experiment, the concentration of the VOC is obtained by monitoring the wavelength drift of output spectrum of the sensor. The experimental results show that when PDMS absorbs the VOC, its volume expands, and the effective bending length of the droplet-type optical fiber structure decreases. The output spectrum of the sensor is blue-shifted when the volume fraction of the VOC ranges from 0 to 9960×10-6. The sensitivity and detection accuracy of the sensor are -0.542 pm/10-6 and 37×10-6, respectively, with a response time of 8.3 min. When the intensity demodulation method is adopted, the sensitivity of the sensor is the highest (-3.22×10-4 dB/10-6) at the wavelength of 1539.00 nm, and its detection accuracy is 31×10-6.

The fractional exhaled nitric oxide (FeNO) is closely related to lung and respiratory diseases. Authorities such as the US Food and Drug Administration (FDA), European Respiratory Society (ERS), and American Thoracic Society (ATS) have successively identified FeNO as an asthma biomarker and listed FeNO as a routine inspection item for respiratory diseases. In order to meet the needs of high-sensitivity monitoring of FeNO, a mid-infrared wavelength modulation laser absorption spectrometer is developed in this paper. The problem of cross interference of CO2 spectral lines is solved by the method of multiple linear regression, and the detection limit of NO reaches 0.12×10-9. The performance of the prototype is calibrated by standard gases with different concentrations, and the linear correlation of the instrument results is 0.994 in the volume fraction range of 0-215×10-9. Finally, the breath samples of volunteers from Xiyuan Hospital of Chinese Academy of Chinese Medical Sciences are measured.

To investigate the factors affecting the visual experience with the TV Ambilight system more deeply, this paper establishes a TV Ambilight simulation system based on the LED light distribution model. The measurement and comparison results show that the simulation system can simulate the light distribution and color fusion of real Ambilight accurately. Experiments designed and accomplished by the simulation system are employed to investigate the factors affecting the perception of Ambilight light effects. The visual perception experimental results indicate that the related factors of LED light intensity and distribution range exert a significant (pp>0.05). The proposed simulation model and preliminary research results can provide a theoretical reference for the design and manufacture of real TV Ambilight systems.