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<jats:p>We investigate experimentally multi-orbital effects in high-order harmonic generation (HHG) from aligned CO<jats:sub>2</jats:sub> and N<jats:sub>2</jats:sub>O molecules by intense femtosecond laser fields with linear and elliptical polarizations. For either of the aligned molecules, a minimum in the harmonic spectrum is observed, the position of which shifts to lower-order harmonics when decreasing the intensity or increasing the ellipticity of the driving laser. This indicates that the minimum originates from the dynamic interference of different channels, of which the tunneling ionization and recombination are contributed via different molecular orbitals. The results show that both the highest occupied molecular orbital (HOMO) and low-lying HOMO-2 in CO<jats:sub>2</jats:sub> (or HOMO-1 in N<jats:sub>2</jats:sub>O) contribute to the molecular HHG in both linearly and elliptically polarized strong laser fields. Our study would pave a way for understanding multi-electron dynamics from polyatomic molecules irradiated by strong laser fields.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Tunnelling, acceleration, and collision of electrons are the basic events in the process of high harmonic generation (HHG) in strong-field interaction with atoms. However, the periodic array of atoms in semiconductor structure makes three steps become interatomic coherent process which leads to complicated carrier dynamics and two sources of high harmonic emission: interband polarization and intraband current. The difference of features of high harmonic generation between semiconductors and atoms is strongly linked to the unique presence of intraband motion which manifests itself a nontrivial role in intertwined two dynamics. Here, we review recent experimental and theoretical advances of understanding coupled interband and intraband mechanisms of HHG in semiconductors. Particularly we focus on the influence of intraband motion on the interband excitation, and on the subsequent HHG emission and attosecond pulse generation.</jats:p>

<jats:p>We <jats:italic>ab initio</jats:italic> investigate the interaction between the hydrogen atom and the inhomogeneous field which is induced by resonant plasmons within a metal nanostructure. Same as normal laser pulse (homogeneous field), only odd-harmonic generation occurs when the bow-tie nanostructure is utilized. For the single nanotip case, the even-harmonic generation can be distinctly found in the harmonic emission spectrum. By investigating the symmetry and trajectories of different inhomogeneous fields, we demonstrate that the breaking symmetry of system can enable even high harmonic generations.</jats:p>

<jats:p>A comparison of differently polarized Bessel vortex beams propagating through a uniaxial anisotropic slab is discussed in terms of the vector wave function expansions. The magnitude profiles of electric field components, the transformation of polarization modes, and the distributions of orbital angular momentum (OAM) states of the reflected and transmitted beams for different incident angles are numerically simulated. The results indicate that the magnitude profiles of electric field components for different polarization modes are distinct from each other and have a great dependence on the incident angle, thus the transformation of polarization modes which reflects the change of energy can be affected largely. As compared to the <jats:italic>x</jats:italic> and circular polarization incidences, the reflected and transmitted beams for the radial polarization incidence suffer the fewest transformation of polarization modes, showing a better energy invariance. The distributions of OAM states of the reflected and transmitted beams for different polarization modes are diverse as well, and the derived OAM states of the transmitted beam for radial polarization present a focusing effect, concentrating on the state between two predominant OAM states.</jats:p>

<jats:p>A new type and easy-to-fabricate metal–insulator–metal (MIM) waveguide reflector based on Sagnac loop is designed and investigated. The transfer matrix theoretical model for the transmission of electric fields in the reflector is established, and the properties of the reflector are studied and analyzed. The simulation results indicate that the reflectivity strongly depends on the coupling splitting ratio determined by the coupling length. Accordingly, different reflectivities can be realized by varying the coupling length. For an optimum coupling length of 750 nm, the 3-dB reflection bandwidth of the MIM waveguide reflector is as wide as <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="0.50em" /> <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_9_094215_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> at a wavelength of 1550 nm, and the peak reflectivity and isolation are 78% and 23 dB, respectively.</jats:p>

<jats:p>The polarization dependences of gain and amplified spontaneous Brillouin scattering (ABS) noise for fiber Brillouin amplifier (FBA) are analyzed through theories, simulations, and experiments. Modified vector propagation equations for calculating the gain of the probe signal and the ABS noise are derived and analyzed in the Stokes spaces. In simulations and experiments, we prove that the gain of the probe signal and the ABS noise are strongly dependent on the relative state of polarization (SOP) of the pump and probe signals. The closer the relative SOP of the pump and probe signals is, the more obvious ABS noise suppression effect will be brought by increasing the power of the input probe signal.</jats:p>

<jats:p>We investigate the sensitivity of phase estimation in a Mach–Zehnder interferometer with photon-subtracted two-mode squeezed vacuum states. Our results show that, for given initial squeezing parameter, both symmetric and asymmetric photon subtractions can further improve the quantum Cramér–Rao bound (<jats:italic>i.e.</jats:italic>, the ultimate phase sensitivity), especially for single-mode photon subtraction. On the other hand, the quantum Cramér–Rao bound can be reached by parity detection for symmetric photon-subtracted two-mode squeezed vacuum states at particular values of the phase shift, but it is not valid for asymmetric photon-subtracted two-mode squeezed vacuum states. In addition, compared with the two-mode squeezed vacuum state, the phase sensitivity via parity detection with asymmetric photon-subtracted two-mode squeezed vacuum states will be getting worse. Thus, parity detection may not always be the optimal detection scheme for nonclassical states of light when they are considered as the interferometer states.</jats:p>

<jats:p>A direct numerical simulation (DNS) method is used to calculate the partitioned convection system with <jats:italic>Ra</jats:italic> number ranging from 10<jats:sup>7</jats:sup> to 2 ×10<jats:sup>9</jats:sup>. Using the boundary layer thickness to normalize the height of gaps <jats:italic>d</jats:italic>, we find a strong consistency between the variation of the TD number (the average value of the temperature in each heat transfer channel is averaged after taking the absolute values) with the change of the height of gaps and the variation of the TD number with the change of <jats:italic>Ra</jats:italic> number in partitioned convection. For a given thickness of partition, heights of gaps are approximately equal to 0.5 or 1 time of the thermal boundary layer thickness <jats:inline-formula> <jats:tex-math><?CDATA ${\lambda }_{\theta }$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>θ</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_094701_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> at different <jats:italic>Ra</jats:italic> numbers. TD number representing temperature characteristics is almost the constant value, which means that TD number is a function of <jats:inline-formula> <jats:tex-math><?CDATA $d/{\lambda }_{\theta }$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>d</mml:mi> <mml:mrow> <mml:mo stretchy="false">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>θ</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_094701_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> only. Analysis of local temperature field of area in gaps shows that the temperature distribution in the gaps are basically the same when <jats:inline-formula> <jats:tex-math><?CDATA $d/{\lambda }_{\theta }$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>d</mml:mi> <mml:mrow> <mml:mo stretchy="false">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>θ</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_094701_ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> is certain. The heat transfer <jats:italic>Nu</jats:italic> number of the system at <jats:inline-formula> <jats:tex-math><?CDATA $d/{\lambda }_{\theta }\approx 0.5$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>d</mml:mi> <mml:mrow> <mml:mo stretchy="false">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>θ</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>0.5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_094701_ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> is larger than that of <jats:inline-formula> <jats:tex-math><?CDATA $d/{\lambda }_{\theta }\approx 1$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>d</mml:mi> <mml:mrow> <mml:mo stretchy="false">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>θ</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>1</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_094701_ieqn5.gif" xlink:type="simple" /> </jats:inline-formula>, both of them have the same scaling law with <jats:italic>Ra</jats:italic> number and <jats:inline-formula> <jats:tex-math><?CDATA ${Nu}\sim {{Ra}}^{0.25}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic">Nu</mml:mi> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mi mathvariant="italic">Ra</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.25</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_094701_ieqn6.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:p>Low density and low convergence implosion occurs in the exploding-pusher target experiment, and generates neutrons isotropically to develop a high yield platform. In order to validate the performance of ShenGuang (SG) laser facility and test nuclear diagnostics, all 48-beam lasers with an on-target energy of 48 kJ were firstly used to drive room-temperature, DT gas-filled glass targets. The optimization has been carried out and optimal drive uniformity was obtained by the combination of beam repointing and target. The final irradiation uniformity of less than 5% on polar direct-drive capsules of <jats:inline-formula> <jats:tex-math><?CDATA $540\,{\rm{\mu }}{\rm{m}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>540</mml:mn> <mml:mspace width="0.50em" /> <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_9_095203_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> in diameter was achieved, and the highest thermonuclear yield of the polar direct-drive DT fuel implosion at the SG was 1.04×10<jats:sup>13</jats:sup>. The experiment results show neutron yields severely depend on the irradiation uniformity and laser timing, and decrease with the increase of the diameter and fuel pressure of the target. The thin CH ablator does not impact the implosion performance, but the laser drive uniformity is important. The simulated results validate that the <jats:inline-formula> <jats:tex-math><?CDATA $\cos \gamma $?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>cos</mml:mi> <mml:mi>γ</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_095203_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> distribution laser design is reasonable and can achieve a symmetric pressure distribution. Further optimization will focus on measuring the symmetry of the hot spot by self-emission imaging, increasing the diameter, and decreasing the fuel pressure.</jats:p>

<jats:p>The experimental knowledge on interlayer potential of graphitic materials is summarized and compared with the computational results based on phenomenological models. Besides Lennard–Jones approximation, the Mie potential is discussed, as well as the Kolmogorov–Crespy model and equation of Lebedeva <jats:italic>et al</jats:italic>. An agreement is found between a set of reported physical properties of graphite (layer binding energies, compressibility along <jats:italic>c</jats:italic>-axis in a broad pressure range, Raman frequencies for bulk shear and breathing modes under pressure), when a proper choice of model parameters is taken. It is argued that anisotropic potentials, Kolmogorov–Crespy and Lebedeva, are preferable for modeling, as they provide a better, self-consistent description. A method of fast numerical modeling, convenient for the accurate estimation of the discussed physical properties, is proposed. It may be useful in studies of other van der Waals homo/heterostructures as well.</jats:p>