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<jats:p>Non-adiabatic dynamical calculations are carried out for the <jats:inline-formula> <jats:tex-math><?CDATA $\mathrm{Na}(3{\rm{p}})+\mathrm{HD}(\nu =1,\ j=0)\to \mathrm{NaH}/\mathrm{NaD}+{\rm{D}}/{\rm{H}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>Na</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>3</mml:mn> <mml:mi mathvariant="normal">p</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>+</mml:mo> <mml:mi>HD</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi>ν</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1</mml:mn> <mml:mo>,</mml:mo> <mml:mspace width="0.33em" /> <mml:mi>j</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mo>→</mml:mo> <mml:mi>NaH</mml:mi> <mml:mrow> <mml:mo stretchy="false">/</mml:mo> </mml:mrow> <mml:mi>NaD</mml:mi> <mml:mo>+</mml:mo> <mml:mi mathvariant="normal">D</mml:mi> <mml:mrow> <mml:mo stretchy="false">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_6_063401_ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> reaction on the diabatic potential energy surfaces of Wang <jats:italic>et al.</jats:italic> (<jats:italic>Sci. Rep.</jats:italic> 2018, <jats:bold>8</jats:bold>, 17960) by using the time-dependent wave packet method. The state-to-state integral cross sections and differential cross sections of two reaction channels (NaH/NaD+D/H) are calculated for collision energy up to 0.4 eV. The cross section branching ratio indicates that the dominant reaction channel changes from NaD+H to NaH+D when the collision energy is larger than 0.227 eV. The products from two reaction channels both prefer to form in vibrationally cold but rotationally hot states, and they both tend to forward scattering.</jats:p>

<jats:p>Cherenkov free electron laser (CFEL) is simulated numerically by using the single particle method to optimize the electron beam. The electron beam is assumed to be moving near the surface of a flat dielectric slab along a growing radiation. The set of coupled nonlinear differential equations of motion is solved to study the electron dynamics. For three sets of parameters, in high power CFEL, it is found that an axial magnetic field is always necessary to keep the electron beam in the interaction region and its optimal strength is reported for each case. At the injection point, the electron beamʼs distance above the dielectric surface is kept at a minimum value so that the electrons neither hit the dielectric nor move away from it to the weaker radiation fields and out of the interaction region. The optimal electron beam radius and current are thereby calculated. This analysis is in agreement with two previous numerical studies for a cylindrical waveguide but is at odds with analytical treatments of a flat dielectric that does not use an axial magnetic field. This is backed by an interesting physical reasoning.</jats:p>

<jats:p>We propose an efficient method of generating a vortex beam with multi-foci by using a fractal spiral zone plate (FSZP), which is designed by combining fractal structure with a spiral zone plate (SZP) in the squared radial coordinate. The theoretical analysis reveals that the number of foci that embed vortices is significantly increased as compared with that obtained by using a conventional SZP. Furthermore, the influence of topological charge on the intensity distribution in focal plane is also discussed in detail. For experimental investigation, an FSZP with topological charge <jats:italic>p</jats:italic> = 1 and 6.4 mm diameter is fabricated by using a photo-etching technique. The calibration indicates that the focusing performances of such a kind of zone plane (ZP) accord well with simulations, thereby providing its potential applications in multi-dimensional optical manipulation and optical imaging technology.</jats:p>

<jats:p>The single-pixel imaging (SPI) technique is able to capture two-dimensional (2D) images without conventional array sensors by using a photodiode. As a novel scheme, Fourier single-pixel imaging (FSI) has been proven capable of reconstructing high-quality images. Due to the fact that the Fourier basis patterns (also known as grayscale sinusoidal patterns) cannot be well displayed on the digital micromirror device (DMD), a fast FSI system is proposed to solve this problem by binarizing Fourier pattern through a dithering algorithm. However, the traditional dithering algorithm leads to low quality as the extra noise is inevitably induced in the reconstructed images. In this paper, we report a better dithering algorithm to binarize Fourier pattern, which utilizes the Sierra–Lite kernel function by a serpentine scanning method. Numerical simulation and experiment demonstrate that the proposed algorithm is able to achieve higher quality under different sampling ratios.</jats:p>

<jats:p>We demonstrated an Fe:ZnSe laser pumped by a 2.93-<jats:inline-formula> <jats:tex-math><?CDATA ${\rm{\mu }}{\rm{m}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_6_064203_ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> Cr, Er:YAG laser at liquid nitrogen and room temperature in single-shot free-running operation for the first time. The xenon flash lamp pumped Cr, Er:YAG laser had a maximum single pulse energy of 1.414 J, and the threshold and slope efficiency were 141.70 J and 0.70% which were respectively reduced by 29.3% and increased by 52.2% compared with the Er:YAG laser. At liquid nitrogen temperature of 77 K, the maximum single pulse energy of the Fe:ZnSe laser was 197.6 mJ, corresponding to a slope efficiency of 13.4%. The central wavelength and full width at half maximum (FWHM) linewidth were 4037.4 nm and 122.0 nm, respectively. At room temperature, the laser generated a maximum single pulse energy of 3.5 mJ at the central wavelength of 4509.6 nm with an FWHM linewidth of 171.5 nm.</jats:p>

<jats:p>Highly nonlinear fibers (HNLFs) are crucial components for supercontinuum (SC) generation with laser solution. However, it is difficult to exactly estimate the structure of produced SC according to material parameters. To give a guideline for choosing and using HNLFs for erbium-fiber-based optical applications, we demonstrate SC generation in five types of HNLFs pumped by 1.57-<jats:inline-formula> <jats:tex-math><?CDATA ${\rm{\mu }}{\rm{m}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_6_064204_ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> laser solitons. All five fibers output a SC exceeding 1000 nm. Three different SC formation processes were observed in the experiment. By comparing optical parameters of these fibers, we find the zero dispersion wavelength (ZDW) of fiber has an important influence on the SC structure and energy distribution for a given pump source.</jats:p>

<jats:p>We demonstrate efficient supercontinuum generation extending into mid-infrared spectral range by pumping a two-mode As<jats:sub>2</jats:sub>S<jats:sub>3</jats:sub> fiber in the normal dispersion regime. The As<jats:sub>2</jats:sub>S<jats:sub>3</jats:sub> fiber is fusion spliced to the pigtail of a near-infrared supercontinuum pump source with ultra-low splicing loss of 0.125 dB, which enables a monolithic all-fiber mid-infrared supercontinuum source. By two-mode excitation and mixed-mode cascaded stimulated Raman scattering, a supercontinuum spanning from <jats:inline-formula> <jats:tex-math> <?CDATA $1.8{\rm{\mu }}{\rm{m}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1.8</mml:mn> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_6_064205_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> to <jats:inline-formula> <jats:tex-math> <?CDATA $4.2{\rm{\mu }}{\rm{m}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>4.2</mml:mn> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_6_064205_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> is obtained. Over 70% of the supercontinuum power is converted to wavelengths beyond <jats:inline-formula> <jats:tex-math> <?CDATA $2.4{\rm{\mu }}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>2.4</mml:mn> <mml:mi mathvariant="normal">μ</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_6_064205_ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> m. This is the first experimental report with respect to the multimode mid-infrared supercontinuum generation in a step-index two-mode chalcogenide fiber.</jats:p>

<jats:p>A comprehensive study on the requirements for the highly efficient third harmonic generation (THG) and its inverse process, one-third harmonic generation (OTHG), in lossy waveguides is proposed. The field intensity restrictions for both THG and OTHG caused by loss are demonstrated. The effective relative phase ranges, supporting the positive growth of signal fields of THG and OTHG are shrunken by the loss. Furthermore, it turns out that the effective relative phase ranges depend on the intensities of the interacting fields. At last, a modified definition of coherent length in loss situation, which evaluates the phase matching degree more precisely, is proposed by incorporating the shrunken relative phase range and the nonlinear phase mismatch. These theoretical analysis are valuable for guiding the experimental designs for highly efficient THG and OTHG.</jats:p>

<jats:p>The compression of high-energy, linearly polarized pulses in a gas-filled hollow core fiber (HCF) by using a concentric phase mask is studied theoretically. Simulation results indicate that using a properly designed concentric phase mask, a 40-fs input pulse centered at 800 nm with energy up to 10.0 mJ can be compressed to a full width at half maximum (FWHM) of less than 5 fs after propagating through a neon-filled HCF with a length of 1 m and diameter of <jats:inline-formula> <jats:tex-math> <?CDATA $500\,{\rm{\mu }}{\rm{m}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>500</mml:mn> <mml:mspace width="0.25em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_6_064207_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> with a transmission efficiency of 67%, which is significantly higher than that without a concentric phase mask. Pulses with energy up to 20.0 mJ can also be efficiently compressed to less than 10 fs with the concentric phase mask. The higher efficiency due to the concentric phase mask can be attributed to the redistribution of the transverse intensity profile, which reduces the effect of ionization. The proposed method exhibits great potential for generating few-cycle laser pulse sources with high energy by the HCF compressor.</jats:p>

<jats:p>Step-coupler waveguide-integrated Ge/Si avalanche photodetector (APD) is based on the vertical multimode interference (MMI), enhancing light scattering towards the Ge active region and creating mirror images of optical modes close to the Ge layer. However, there are two ineluctable contact angels between selectively epitaxial growth Ge and Si layers and selectively epitaxial growth Si and Si substrate, which has an effect on the coupling efficiency and the absorption of the photodetector. Therefore, step-coupled Ge/Si avalanche photodetectors with different step lengths are designed and fabricated. It is found that responsivity of APDs with step-coupler-length of <jats:inline-formula> <jats:tex-math> <?CDATA $3.0\,{\rm{\mu }}{\rm{m}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>3.0</mml:mn> <mml:mspace width="0.25em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_6_064208_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> is 0.51 A/W at −6 V, 21% higher than that of <jats:inline-formula> <jats:tex-math> <?CDATA $1.5\,{\rm{\mu }}{\rm{m}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1.5</mml:mn> <mml:mspace width="0.25em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_6_064208_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, which matches well with simulation absorption. The multiplication gain factor is as high as 50, and the maximum gain-bandwidth product reaches up to 376 GHz.</jats:p>