查看更多>>摘要：Rydberg state excitation(RSE)is a highly non-linear physical phenomenon that is induced by the ionization of atoms or molecules in strong femtosecond laser fields.Here we observe that both parent and fragments(S,C,OC)of the tri-atomic molecule carbonyl sulfide(OCS)can survive strong 800 nm or 400 nm laser fields in high Rydberg states.The dependence of parent and fragment RSE yields on laser intensity and ellipticity is investigated in both laser fields,and the results are compared with those for strong-field ionization.Distinctly different tendencies for laser intensity and ellipticity are observed for fragment RSE compared with the corresponding ions.The mechanisms of RSE and strong-field ionization of OCS molecules in different laser fields are discussed based on the experimental results.Our study sheds some light on the strong-field excitation and ionization of molecules irradiated by femtosecond NIR and UV laser fields.
查看更多>>摘要：We study the dynamical evolution of cold atoms in crossed optical dipole trap theoretically and experimentally.The atomic transport process is accompanied by two competitive kinds of physical mechanics,atomic loading and atomic loss.The loading process normally is negligible in the evaporative cooling experiment on the ground,while it is significant in preparation of ultra-cold atoms in the space station.Normally,the atomic loading process is much weaker than the atomic loss process,and the atomic number in the central region of the trap decreases monotonically,as reported in previous research.However,when the atomic loading process is comparable to the atomic loss process,the atomic number in the central region of the trap will initially increase to a maximum value and then slowly decrease,and we have observed the phenomenon first.The increase of atomic number in the central region of the trap shows the presence of the loading process,and this will be significant especially under microgravity conditions.We build a theoretical model to analyze the competitive relationship,which coincides with the experimental results well.Furthermore,we have also given the predicted evolutionary behaviors under different conditions.This research provides a solid foundation for further understanding of the atomic transport process in traps.The analysis of loading process is of significant importance for preparation of ultra-cold atoms in a crossed optical dipole trap under microgravity conditions.
查看更多>>摘要：The aim of this study is to numerically investigate the impact of boundary slip on electroosmotic flow(EOF)in curved rectangular microchannels.Navier slip boundary conditions were employed at the curved microchannel walls.The electric potential distribution was governed by the Poisson-Boltzmann equation,whereas the velocity distribution was determined by the Navier-Stokes equation.The finite-difference method was employed to solve these two equations.The detailed dis-cussion focuses on the impact of the curvature ratio,electrokinetic width,aspect ratio and slip length on the velocity.The results indicate that the present problem is strongly dependent on these parameters.The results demonstrate that by varying the dimensionless slip length from 0.001 to 0.01 while maintaining a curvature ratio of 0.5 there is a twofold increase in the maximum velocity.Moreover,this increase becomes more pronounced at higher curvature ratios.In addition,the velocity difference between the inner and outer radial regions increases with increasing slip length.Therefore,the incorporation of the slip boundary condition results in an augmented velocity and a more non-uniform velocity distribution.The find-ings presented here offer valuable insights into the design and optimization of EOF performance in curved hydrophobic microchannels featuring rectangular cross-sections.
查看更多>>摘要：Modern trends in beam-driven radiation sources include the interaction of Cherenkov wakefields in open-ended cir-cular waveguides with complicated dielectric linings,with a three-layer dielectric capillary recently proposed to reduce radiation divergence being a representative example[Opt.Lett.45 5416(2020)].We present a rigorous approach that allows for an analytical description of the electromagnetic processes that occur when the structure is excited by a single waveguide TM mode.In other words,the corresponding canonical waveguide diffraction problem is solved in a rigorous formulation.This is a continuation of our previous papers which considered simpler cases with a homogeneous or two-layer dielectric filling.Here we use the same analytical approach based on the Wiener-Hopf-Fock technique and deal with the more complicated case of a three-layer dielectric lining.Using the obtained rigorous solution,we discuss the possibility of manipulating the far-field radiation pattern using a third layer made of a low permittivity material.
查看更多>>摘要：Coherent beam combining(CBC)of fiber laser array is a promising technique to realize high output power while maintaining near diffraction-limited beam quality.To implement CBC,an appropriate phase control feedback structure should be established to realize phase-locking.In this paper,an innovative internal active phase control CBC fiber laser array based on photodetector array is proposed.The dynamic phase noises of the laser amplifiers are compensated before being emitted into free space.And the static phase difference compensation of emitting laser array is realized by interference measurement based on photodetector array.The principle of the technique is illustrated and corresponding simulations are carried out,and a CBC system with four laser channels is built to verify the technique.When the phase controllers are turned on,the phase deviation of the laser array is less than λ/20,and～95％fringe contrast of the irradiation distribution is obtained.The technique proposed in this paper could provide a reference for the system design of a massive high-power CBC system.
查看更多>>摘要：We take phase modulation to create discrete phase-controlled sources and realize the super-bunching effect by a phase-correlated method.From theoretical and numerical simulations,we find the space translation invariance of the bunching effect is a key point for the ghost imaging realization.Experimentally,we create the orderly phase-correlated discrete sources which can realize high-visibility second-order ghost imaging than the result with chaotic sources.Moreover,some factors affecting the visibility of ghost image are discussed in detail.
查看更多>>摘要：Photonic spin Hall effect(PSHE),as a novel physical effect in light-matter interaction,provides an effective metro-logical method for characterizing the tiny variation in refractive index(RI).In this work,we propose a multi-functional PSHE sensor based on VO2,a material that can reveal the phase transition behavior.By applying thermal control,the mu-tual transformation into different phase states of VO2 can be realized,which contributes to the flexible switching between multiple RI sensing tasks.When VO2 is insulating,the ultrasensitive detection of glucose concentrations in human blood is achieved.When VO2 is in a mixed phase,the structure can be designed to distinguish between the normal cells and cancer cells through no-label and real-time monitoring.When VO2 is metallic,the proposed PSHE sensor can act as an RI indicator for gas analytes.Compared with other multi-functional sensing devices with the complex structures,our design consists of only one analyte and two VO2 layers,which is very simple and elegant.Therefore,the proposed VO2-based PSHE sensor has outstanding advantages such as small size,high sensitivity,no-label,and real-time detection,providing a new approach for investigating tunable multi-functional sensors.
查看更多>>摘要：Based on numerical solutions of the time-dependent Schrödinger equation,we theoretically investigate the photoelec-tron spectrum of hydrogen atoms ionized by a pair of ultrashort,intense,and orthogonally polarized laser pulses with a relative time delay in a pump-probe configuration.The pump pulse resonantly excites electrons from the 1s and 2p levels,inducing Rabi oscillations.The resulting dynamically enhanced Autler-Townes(AT)splitting is observed in the photo-electron energy spectrum upon interaction with the second probe pulse.In contrast to the previous parallel-polarization scheme,the proposed orthogonal-polarization configuration enables the resolution of dynamically enhanced AT splitting over a considerably wider range of probe photon energies.
查看更多>>摘要：Limited by the thermal environment,the entanglement of a massive object is extremely difficult to generate.Based on a coherent scattering mechanism,we propose a scheme to generate the entanglement of two optically levitated nanospheres through the Coulomb interaction.Two nanospheres are charged and coupled to each other through the Coulomb interaction.In this manner,the entanglement of two nanospheres is induced either under a weak/strong optomechanical coupling regime or under an ultra-strong optomechanical coupling regime.The charges,radius and distance of the two nanospheres are taken into consideration to enhance the Coulomb interaction,thereby achieving a higher degree of entanglement in the absence of ground-state cooling.The corresponding maximum entanglement can be attained as the dynamics of the system approaches the boundary between the steady and the unsteady regimes.This provides a useful resource for both quantum-enhanced sensing and quantum information processing,as well as a new platform for studying many-body physics.
查看更多>>摘要：A high-performance LED-side-pumped two-rod Nd,Ce∶YAG laser with continuous-wave(CW)and acousto-optical(A-O)Q-switched operation is demonstrated in this work.A symmetrically shaped flat-flat cavity with two identical LED-side-pumped laser modules is employed for power scalability.In the CW regime,the maximum output average power of laser at 1064 nm is 4.41 W,corresponding to a maximum optical conversion efficiency of 5.3％and a slope efficiency is 12.4％.In the active Q-switched regime,the pulse energy of laser reaches as high as 0.89 mJ at a repetition rate of 800 Hz with a pulse width of 457.2 ns,the corresponding highest peak output power is 1.94 kW and the M2 factor is measured to be about 8.8.To the best of the authors'knowledge,this is the first demonstration and the highest performance of a CW LED-side-pumped two-rod laser Nd,Ce∶YAG with Watt-level output reported so far.
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