Catálogo de publicaciones - revistas

<jats:p>We investigate the intensity effect of ultrashort assisting infrared laser pulse on the single-XUV-photon double ionization of helium atoms by solving full six-dimensional time-dependent Schrödinger equation with implement of finite element discrete variable representation. The studies of joint energy distributions and joint angular distributions of the two photoelectrons reveal the competition for ionized probabilities between the photoelectrons with odd parity and photoelectrons with even parity in single-XUV-photon double ionization process in the presence of weak infrared laser field, and such a competition can be modulated by changing the intensity of the weak assisting-IR laser pulses. The emission angles of the two photoelectrons can be adjusted by changing the laser parameters as well. We depict how the assisting-IR laser field enhances and/or enables the back-to-back and side-by-side emission of photoelectrons created in double ionization process.</jats:p>

<jats:p>Kinetic investigations including quasi-classical trajectory and canonical unified statistical theory method calculations are carried out on a potential energy surface for the hydrogen-abstraction reaction from methane by atom O(<jats:sup>3</jats:sup>P). The surface is constructed using a modified Shepard interpolation method. The <jats:italic>ab initio</jats:italic> calculations are performed at the CCSD(T) level. Taking account of the contribution of inner core electrons to electronic correlation interaction in <jats:italic>ab initio</jats:italic> electronic structure calculations, modified optimized aug-cc-pCVQZ basis sets are applied to the all-electrons calculations. On this potential energy surface, the triplet oxygen atom attacks methane in a near-collinear H–CH<jats:sub>3</jats:sub> direction to form a saddle point with barrier height of 13.55 kcal/mol, which plays a key role in the kinetics of the title reaction. For the temperature range of 298–2500 K, our calculated thermal rate constants for the O(<jats:sup>3</jats:sup>P) + CH<jats:sub>4</jats:sub> → OH + CH<jats:sub>3</jats:sub> reaction show good agreement with relevant experimental data. This work provides detailed mechanism of this gas-phase reaction and a theoretical guidance for methane combustion.</jats:p>

<jats:p>For an atomic gravimeter, the measured value of the Earth’s gravity acceleration <jats:italic>g</jats:italic> is the projection of the local gravity on the direction of Raman laser beams. To accurately measure the <jats:italic>g</jats:italic>, the Raman laser beams should be parallel to the <jats:italic>g</jats:italic> direction. We analyze the tilt effect of the Raman beams on <jats:italic>g</jats:italic> measurement and present a general method for the tilt adjustment. The systematic error caused by the tilt angle is evaluated as 0 (+0, –0.8) μGal (1μGal = 10 nm/s<jats:sup>2</jats:sup>) and the drift is also compensated in real time. Our method is especially suitable for the portable atomic gravimeter which focuses on the mobility and field applications.</jats:p>

<jats:p>We used discrete dipole approximation (DDA) to examine the scattering and absorption characteristics of spherical ice crystal particles. On this basis, we studied the scattering characteristics of spherical ice crystal particles at different frequencies and non-spherical ice crystal particles with different shapes, aspect ratios, and spatial orientations. The results indicate that the DDA and Mie methods yield almost the same results for spherical ice crystal particles, illustrating the superior calculation accuracy of the DDA method. Compared with the millimeter wave band, the terahertz band particles have richer scattering characteristics and can detect ice crystal particles more easily. Different frequencies, shapes, aspect ratios, and spatial orientations have specific effects on the scattering and absorption characteristics of ice crystal particles. The results provide an important theoretical basis for the design of terahertz cloud radars and related cirrus detection methods.</jats:p>

<jats:p>Spatial filtering velocimetry (SFV) has the advantages of simple structure, good stability, and wide applications. However, the traditional linear CCD-based SFV method requires an accurate angle between the direction of linear CCD and the direction of moving object, so it is not suitable for measuring a complex flow field or two-dimensional speed in a granular media. In this paper, a new extension of spatial filtering method (SFM) based on high speed array CCD camera is proposed as simple and effective technique for measuring two-dimensional speed field of granular media. In particular, we analyzed the resolution and range of array CCD-based SFV so that the reader can clarify the application scene of this method. This method has a particular advantage for using orthogonal measurement to avoid the angle measurement, which were problematic when using linear CCD to measure the movement. Finally, the end-wall effects of the granular flow in rotating drum is studied with different experimental conditions by using this improved technique.</jats:p>

<jats:p>The attosecond ionization dynamics of atoms has attracted extensive attention in these days. However, the role of the initial state is not clearly understood. To address this question, we perform simulations on the neon atom and its model atom with different initial states by numerically solving the corresponding two-dimensional time-dependent Schrödinger equations. We theoretically investigate atomic photoelectron momentum distributions (PMDs) by a pair of elliptically polarized attosecond laser pulses. We find that the PMD is sensitive not only to the ellipticities of the pulses, the relative helicity, and time delay of the pulses, but also to the symmetry of the initial electronic states. Results are analyzed by the first-order time-dependent perturbation theory (TDPT) and offer a new tool for detecting the rotation direction of the ring currents.</jats:p>

<jats:p>A Yb-doped CaF<jats:sub>2</jats:sub> transparent ceramics was successfully fabricated by the hot-pressed method and its laser characteristics were studied. A broad tuning performance and mode-locked laser operation were demonstrated in this ceramics for the first time, to our best knowledge. A 60-nm continuous-wavelength tunable laser from 1019 nm to 1079 nm was obtained with a birefringent filter. By employing a semiconductor saturable absorber mirror without additional dispersion compensation elements, a continuous-wave mode-locked laser with pulse duration as short as 575 fs was delivered, at a central wavelength of 1048.5 nm. The oscillator is operated under a repetition rate of 55 MHz. These results indicate that the Yb:CaF<jats:sub>2</jats:sub> transparent ceramics is an ideal candidate for the development of ultrafast lasers in the near-infrared regime.</jats:p>

<jats:p>We demonstrate a self-started, long-term stable polarization-maintaining mode-locked fiber laser based on the nonlinear polarization evolution technique. A polarized beam splitter is inserted into the cavity of the linear polarization-maintaining fiber laser to facilitate self-started mode-locking. Pulses with single pulse energy of 26.9 nJ and average output power of 73.9 mW are obtained at the pump power of 600 mW. The transmission characteristics of artificial saturable absorber used in this laser are analyzed theoretically, the influence of the half-wave plate state on mode-locking is discussed, and the mode-locking range is obtained, which is well consistent with the experimental results.</jats:p>

<jats:p>The Advanced Space-based Solar Observatory (ASO-S) is a mission proposed by the Chinese Solar Physics Community. As one of the three payloads of ASO-S, the Full-disc Magneto-Graph (FMG) will measure the photospheric magnetic fields of the entire solar disk with high spatial and temporal resolution, and high magnetic sensitivity, where liquid crystal variable retarder (LCVR) is the key to whether FMG can achieve its scientific goal. So far, there is no space flight experience for LCVR. Therefore, irradiation study for LCVRs becomes more important and urgent in order to make sure their safety and reliability in space application. In this paper, <jats:italic>λ</jats:italic> irradiation, proton irradiation, and ultra-violet (UV) irradiation are tested for LCVRs respectively. The optical and chemical properties during irradiation tests are measured and analyzed. For optical properties, there is no significant change in those parameters FMG payload concerned except the retardation. Although there is no drastic degradation in the retardation <jats:italic>versus</jats:italic> voltage during irradiations, the amount of retardation variation is much higher than the instrument requirements. Thus, an in-flight retardation <jats:italic>versus</jats:italic> voltage should be added in FMG payload, reducing or even avoiding the impact of retardation change. For chemical properties, the clearing point and birefringence of the LC materials almost have no change; the ion density dose not change below 60 krad[Si], but begin to increase dramatically above 60 krad[Si].</jats:p>

<jats:p>Progress of the <jats:sup>40</jats:sup>Ca<jats:sup>+</jats:sup> ion optical clock based on the 4<jats:sup>2</jats:sup>S<jats:sub>1/2</jats:sub> – 3d <jats:sup>2</jats:sup>D<jats:sub>5/2</jats:sub> electric quadrupole transition is reported. By setting the drive frequency to the “magic” frequency <jats:italic>Ω</jats:italic> <jats:sub>0</jats:sub>, the frequency uncertainty caused by the scalar Stark shift and second-order Doppler shift induced by micromotion is reduced to the 10<jats:sup>−19</jats:sup> level. By precisely measuring the differential static scalar polarizability Δ<jats:italic>α</jats:italic> <jats:sub>0</jats:sub>, the uncertainty due to the blackbody radiation (BBR) shift (coefficient) is reduced to the 10<jats:sup>−19</jats:sup> level. With the help of a second-order integrating servo algorithm, the uncertainty due to the servo error is reduced to the 10<jats:sup>−18</jats:sup> level. The total fractional uncertainty of the <jats:sup>40</jats:sup>Ca<jats:sup>+</jats:sup> ion optical clock is then improved to 2.2× 10<jats:sup>−17</jats:sup>, whereas this value is mainly restricted by the uncertainty of the BBR shift due to temperature fluctuations. The state preparation is introduced together with improvements in the pulse sequence, and furthermore, a better signal to noise ratio (SNR) and less dead time are achieved. The clock stability of a single clock is improved to <jats:inline-formula> <jats:tex-math><?CDATA $4.8\times {10}^{-15}/\sqrt{\tau}\,({\rm{in}}\,{\rm{seconds}})$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>4.8</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>15</mml:mn> </mml:mrow> </mml:msup> <mml:mo>/</mml:mo> <mml:msqrt> <mml:mi>τ</mml:mi> </mml:msqrt> <mml:mspace width="0.25" /> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">in</mml:mi> <mml:mspace width="0.25" /> <mml:mi mathvariant="normal">seconds</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_7_074209_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>