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<jats:p>The spectral attenuation of a 400-nm probe laser propagating through a femtosecond plasma in air is studied. Defocusing effect of the low-density plasma is an obvious effect by examining the far-field patterns of the 400-nm pulse. Besides, the energy of 400-nm pulse drops after interaction with the plasma, which is found to be another effect leading to the attenuation. To reveal the physical origin behind the energy loss, we measure fluorescence emissions of the interaction area. The fluorescence is hardly detected with the weak 400-nm laser pulse, and the line spectra from the plasma filament induced by the 800-nm pump pulse are clearly shown. However, when the 400-nm pulse propagates through the plasma filament, the fluorescence at 391 nm from the first negative band system of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{N}}}_{2}^{+}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi mathvariant="normal">N</mml:mi> <mml:mn>2</mml:mn> <mml:mo>+</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_1_013301_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> is enhanced, while that from the second positive band of neutral N<jats:sub>2</jats:sub> at 337 nm remains constant. Efficient near-resonant absorption of the 400-nm pulse by the first negative band system occurs inside the plasma, which results in the enhanced fluorescence. Furthermore, the spectral attenuation of the 400-nm probe laser is measured as a function of the pump–probe time delay as well as the pump-pulse energy.</jats:p>

<jats:p>In this review, we will focus on recent progress on the investigations of nondipole effects in few-electron atoms and molecules interacting with light fields. We first briefly survey several popular theoretical methods and relevant concepts in strong field and attosecond physics beyond the dipole approximation. Physical phenomena stemming from the breakdown of the dipole approximation are then discussed in various topics, including the radiation pressure and photon-momentum transfer, the atomic stabilization, the dynamic interference, and the high-order harmonic generation. Whenever available, the corresponding experimental observations of these nondipole effects are also introduced respectively in each topics.</jats:p>

<jats:p>The electron capture processes in collisions of Li<jats:sup>3+</jats:sup> ion with Li(1s<jats:sup>2</jats:sup>2s) and Li(1s<jats:sup>2</jats:sup>2p<jats:sub>0,1</jats:sub>) are investigated by using the two-center atomic orbital close-coupling method in the energy range from 0.1 keV/u to 300 keV/u. The interaction of the active electrons with the target ion is represented by a model potential. The present results for the Li<jats:sup>3+</jats:sup>–Li(1s<jats:sup>2</jats:sup>2s) system are compared with the available theoretical data and general agreement is obtained for the high collision energies. It is also found that the total and partial electron capture cross sections are sensitive to the initial charge cloud alignment in the low energy region.</jats:p>

<jats:p>It is desirable to have electromagnetic wave absorbers with ultrathin structural thickness and broader spectral absorption bandwidth with numerous applications in optoelectronics. In this paper, we theoretically propose and numerically demonstrate a novel ultrathin nanostructure absorber composed of semiconductor nanoring array and a uniform gold substrate. The results show that the absorption covers the entire visible light region, achieving an average absorption rate more than 90% in a wavelength range from 300 nm to 740 nm and a nearly perfect absorption from 450 nm to 500 nm, and the polarization insensitivity performance is particularly great. The absorption performance is mainly caused by the electrical resonance and magnetic resonance of semiconductor nanoring array as well as the field coupling effects. Our designed broadband visible light absorber has wide application prospects in the fields of thermal photovoltaics and photodetectors.</jats:p>

<jats:p>Generation of noise-like rectangular pulse was investigated systematically in an Er–Yb co-doped fiber laser based on an intra-cavity coupler with different coupling ratios. When the coupling ratio was 5/95, stable mode-locked pulses could be obtained with the pulse packet duration tunable from 4.86 ns to 80 ns. The repetition frequency was 1.186 MHz with the output spectrum centered at 1.6 μm. The average output power and single pulse energy reached a record 1.43 W and 1.21 μJ, respectively. Pulse characteristics under different coupling ratios (5/95, 10/90, 20/80, 30/70, 40/60) were also presented and discussed.</jats:p>

<jats:p>The propagation characteristic of two identical and parallel dark solitons in a silicon-on-insulator (SOI) waveguide is simulated numerically using the split-step Fourier method. The parallel dark solitons imposed by the initial chirp are investigated mainly by changing their power, their relative time delay. The simulation shows that the time delay deforms the parallel dark soliton pulse, forming a bright-like soliton in the transmission process and making the transmission quality down. By increasing the power of one dark soliton, the energy of the other dark soliton can be increased, and larger increase in a soliton’s power leads to larger increase in the energy of the other. When the initial chirp is introduced into one of the dark solitons, higher energy consumption is observed. In particular, positive chirps resulting in pulse broadening width while negative chirps narrowing, with an obvious compression effect on the other dark soliton. Finally, large negative chirps are found to have a profound impact on parallel and nonparallel dark solitons.</jats:p>

<jats:p>Soliton dynamics are numerically investigated in a two-mode fiber with the two-photon absorption, and the effects of the two-photon absorption on the soliton propagation and interaction are demonstrated in different dispersion regimes. Soliton dynamics depend strictly on the sign and magnitude of the group velocity dispersion (GVD) coefficient of each mode and the strength (coefficient) of the two-photon absorption. The two-photon absorption leads to the soliton collapse, enhances the neighboring soliton interaction in both modes, and increases the energy exchange between the two modes. Finally, an available control is proposed to suppress the effects by the use of the nonlinear gain with filter.</jats:p>

<jats:p>A stable and accurate pointing, acquisition system is an important part of initially building intersatellite optical communication links. Satellite platform vibration can cause the system instability and reduce the system precision in building and maintenance of a satellite optical communication system. In this paper, vibration influence is consciously discussed by acquisition time for intersatellite optical communications. Analytical expression of acquisition possibility is derived, taking the scan parameters and platform vibration into account, and vibration influence on the multi-scan acquisition time is also presented. The theoretical result calculated by the proposed analytical expression is approximate to the result by the Monte Carlo simulation.</jats:p>

<jats:p>An explanation of optical unitary transformation is presented for general nonoverlapping-image multimode interference (MMI) couplers with any number of input and output ports. The light transformation in the MMI coupler can be considered as an optical field matrix acting on an input light column vector. We investigate the general phase principle of output light image. The complete proof of nonoverlapping-image MMI coupler’s optical unitarity along with the phase analysis of matrix element is provided. Based on a two-dimensional finite-difference time-domain (2D-FDTD) simulation, the unitary transformation is obtained for a 4 × 4 nonoverlapping-image MMI coupler within a deviation of 4 × 10<jats:sup>−2</jats:sup> for orthogonal invariance and 8 × 10<jats:sup>−2</jats:sup> for transvection invariance in the C-band spectral range. A compact 1 × 4 splitter based on cascaded MMI coupler is proposed, showing a phase deviation less than 5.4° while maintaining a low-loss performance in C-band spectra.</jats:p>

<jats:p>We propose a vectorial optical field generation system based on two-dimensional blazed grating to high-efficiently generate structured optical fields with prescribed amplitude, phase, and polarization. In this system, an optimized blazed grating hologram is written on a spatial light modulator (SLM) and can diffract the majority of the incident light into the first-order diffractions of the <jats:italic>x</jats:italic> and <jats:italic>y</jats:italic> directions, which then serve as base vectors for synthesizing desired vector beams. Compared with the conventional cosine grating used in the previous work, the proposed two-dimensional, blazed grating has a much higher efficiency. Both computer simulation and optical experiment validate that a conversion efficiency up to 5 times that of the former work is achieved. Our method can facilitate applications of the optical field manipulation.</jats:p>