We theoretically investigate the contribution of the excited state to the ellipticity of the harmonics from H＋ at different orientation angles irradiated by a linearly polarized laser pulse. It is found that the first excited state has a significant influence to the ellipticity of the harmonics, and the contribution of higher excited states to the ellipticity can be neglected. Moreover, the conclusion is not dependent on the laser intensity.
In this work, the program Cindy was modified to calculate the formation cross section of each energy level of residual nucleus lSlw resulting from the reaction lSlTa（p,n2/）lSlw. The concerned cross sections calculated at proton energy Ep=4.5-8.5 MeV agreed well with experimental results. The influence of the spin cut-off parameter in the energy level density model on the cross section was studied. The obtained results show that the influence of spin cut-off is obvious for lower energy levels.
We propose a theoretical scheme to generate a broadband supercontinuum using a modulated chirped polarization gating technique. By this technique, a broadband continuum of 155 eV can be obtained at microscopic level. The modulations on the supercontinuum can be eliminated after propagation. Then a smooth broadband supercontinuum with the bandwidth of 155 eV can be generated. As a result, isolated sub-100-attosecond pulses with tunable central wavelengths could be obtained straightforwardly. Our simulations also reveal that an isolated attosecond pulse can still be generated by using multicycle driving laser pulses, and the central wavelength of isolated attosecond pulse can be controlled by adjusting the delay τd (τd is the delay of the two counter-rotating circularly polarized pulses.).
A digital coincidence acquisition system applied to a portable liquid scintillation counting device is developed. The system which simplifies the device design consists of a digitizer card of Agilent U1066A DC438, a discriminator and a host computer. The anode analog pulses from two photomultiplier tubes are captured by the system, which adopts the sequence acquisition storage mode. By choosing proper threshold for each channel, coincidence time window of ±30 ns, and comparing the pulse amplitudes from two channels, the portable scintillation counting device can be used to detect β particles. For the unquenched standard 3 H sample, the results show that the detection efficiency is (58.5±0.1)% and the background is (86.7±0.7) cpm. Meanwhile, 3 H β spectrum is obtained.
Single-pulse and double-pulse optical emission spectroscopy （OES） analyses were carried out in air by using ultrashort laser pulses at atmospheric pressure. The aim of this work is to use spectroscopic methods to analyze the early phase of laser-induced plasma after the femtosecond laser pulse. The temporal behavior of emission spectra of air plasma has been characterized. In comparison with the single-pulse scheme, the plasma emission obtained in the double-pulse scheme presents a more intense continuum along with several additional ionic lines. As only one line is available in the single-pulse scheme, the plasma temperature measurements were performed using only the relative line-to-continuum intensity ratio method, whereas the relative line-to-line intensity ratio method and the relative line-to-continuum intensity ratio method were used simultaneously to estimate the electron temperature in the double-pulse scheme. The results reveal that the temperature values obtained by the two methods in the double-pulse scheme agree. Moreover, this shows that the relative line-to-continuum intensity ratio method is suitable for early phase of laser-induced plasma diagnostics. The electron number density was estimated using the Stark broadening method. In the early phase of laser-induced plasma, the temporal evolution of the electron number density exhibits a power law decrease with delay time.
We theoretically investigate the electron dynamics of the high-order harmonics generation process by combining a near-infrared 800 nm driving pulse with a mid-infrared 2000 nm control field. We also investigate the emission time of harmonics using time-frequency analysis to illustrate the physical mechanisms of high-order harmonic generation. We calculate the ionization rate using the Ammoso Delone-Krainov model and interpret the variations in harmonic intensity for different control field strengths and delays. We find that the width of the harmonic plateau can be extended when the control electric field is added, and a supercontinuum from 198 to 435 eV is generated, from which an isolated 61-as pulse can be directly obtained.
Within the framework of the dynamical classical over-barrier model,the soft collisions between slow highly charged ions（SHCIs） Ar 17＋ and the large copper clusters under large impact parameters have been studied in this paper.We present the dominant mechanism of the electron transfer between SHCIs and a large metal cluster by computational simulation.The evolution of the occupation of projectile ions,KL x satellite lines,X-ray yields,Auger electron spectrum and scattering angles are provided.
