No abstract

The defined oxidation ability of metallurgical slags based on the ion and molecule coexistence theory (IMCT), i.e., the comprehensive mass action concentration N FetO of iron oxides, has been verified through comparing the calculated N FetO and the reported activity a FetO of iron oxides in the selected Fe t O-containing slag systems. To calculate the defined comprehensive mass action concentration N FetO of iron oxides in the selected slag systems, a thermodynamic model for calculating the mass action concentrations of structural units or ion couples in CaO-SiO 2 -MgO-FeO-Fe 2 O 3 -MnO-Al 2 O 3 -P 2 O 5 type slags, i.e., the IMCT-N i thermodynamic model, has been developed. The defined comprehensive mass action concentration N FetO of iron oxides is more accurate than the measured activity a FetO of iron oxides to represent the slag oxidation ability of the selected Fe t O-containing slag systems. The calculated comprehensive mass action concentration N FetO of iron oxides or the reported activity a FetO of iron oxides in the selected Fe t O-containing slag systems shows an increase tendency with an increase of optical basicity of the slags by taking L FeO as 0.93 and L Fe 2 O 3 as 0.69, or L FeO as 1.0 and L Fe 2 O 3 as 0.75, rather than by taking L FeO as 0.51 and L Fe 2 O 3 as 0.48. The slag oxidation ability represented by the defined comprehensive mass action concentration N FetO of iron oxides or the measured activity a FetO of iron oxides is not only decided by the effects of iron oxides, but also by the comprehensive effects of both iron oxides and basic oxides as CaO or MgO or MnO in the selected Fe t O-containing slag systems.[ Ã ] X.

Near- and below-threshold harmonic generation provides a potential approach to generate vacuum-ultraviolet frequency comb. However, the dynamical origin of in these lower harmonics is less understood and largely unexplored. Here we perform an ab initio quantum study of the near- and below-threshold harmonic generation of caesium (Cs) atoms in an intense 3,600-nm mid-infrared laser field. Combining with a synchrosqueezing transform of the quantum time-frequency spectrum and an extended semiclassical analysis, the roles of multiphoton and multiple rescattering trajectories on the near- and below-threshold harmonic generation processes are clarified. We find that the multiphoton-dominated trajectories only involve the electrons scattered off the higher part of the combined atom-field potential followed by the absorption of many photons in near- and below-threshold regime. Furthermore, only the near-resonant below-threshold harmonic is exclusive to exhibit phase locked features. Our results shed light on the dynamic origin of the near- and below-threshold harmonic generation.

We propose an efficient method for the generation of ultrabroadband supercontinuum spectra and isolated ultrashort attosecond laser pulses from He atoms with two-color midinfrared laser fields. High-order harmonic generation (HHG) is obtained by solving the time-dependent Schrödinger equation accurately by means of the time-dependent generalized pseudospectral method. We found that the optimizing two-color midinfrared laser pulse allows the HHG cutoff to be significantly extended, leading to the production of an ultrabroadband supercontinuum. As a result, an isolated 18-attosecond pulse can be generated directly by the superposition of the supercontinuum harmonics. To facilitate the exploration of the ultrashort attosecond generation mechanisms, we perform both a semiclassical simulation and a wavelet time-frequency transform.

We present an ab initio investigation of the below-threshold harmonic generation of helium (He) atoms in few-cycle infrared laser fields by accurately solving the time-dependent Schrödinger equation and Maxwell's equation simultaneously. We find that the enhancement of the below-threshold harmonic generation only occurs to near the resonance structure of He, for which this mechanism is in agreement with the recent experimental study [M. Chini et al., Nat. Photonics 8, 437 (2014)]. Moreover, we perform the quantum and semiclassical trajectories analysis, including both the atomic potential and the laser field, as well as the synchrosqueezed transform of the harmonic spectra. Our results reveal that several multirescattering trajectories contribute to the resonance-enhanced below-threshold harmonic generation.High-order-harmonic generation (HHG) of atoms and molecules in intense laser fields, leading to the production of the coherent extreme-ultraviolet and attosecond pulses, has attracted much interest in the subject of ultrafast science and technology in the last decade [1-6]. The essential features in HHG, such as the above-threshold harmonic plateau and cutoffs, can be well understood by the semiclassical threestep model [7,8]. The HHG cutoff occurs approximately at the energy I p + 3.17U p , where I p is the atomic ionization potential, and U p is the ponderomotive potential. Furthermore, the strong field approximation (SFA) [9] has been commonly adopted for studying the HHG above the ionization threshold. However, due to its complete neglect of the intermediate bound states and the Coulomb interaction in the final state, the SFA is not accurate to describe the below-threshold harmonic generation (HHG below the ionization threshold). In this Rapid Communication, we present an ab initio study of the below-threshold harmonic generation by accurately solving the time-dependent Schrödinger equation (TDSE). To simulate the propagation effects, we also solve the Maxwell equation simultaneously.Recently, as a promising method to produce vacuumultraviolet (VUV) frequency comb, the number of studies of HHG in the near-and below-ionization threshold has been increased considerably. Yost et al. [10] have studied the VUV frequency comb from below-threshold harmonic generation in xenon irradiated by an intense infrared laser field. They presented the first explicit VUV frequency comb structure beyond the third harmonic. In addition, Power et al. [11] have found that the generation of below-threshold harmonics is dominated by long trajectories, via a nonperturbative approach. Hostetter et al. [12] have extended the semiclassical three-step model with the atomic potential for the treatment of * lipc@nwnu.edu.cn † sichu@ku.edu below-threshold harmonic processes in a model atom. Soifer et al. [13] have studied near-threshold HHG from the aligned molecules. More recently, Michael Chini et al. [14] have demonstrated a new regime of phase-matched below-threshold harmonic generation, for which the generation and phase matching [15...

No abstract

We present an efficient high-order-harmonic optimal control scheme for the generation of the ultrabroad supercontinuum spectrum and an isolated ultrashort attosecond pulse in gases with a two-color mid-IR laser field. The optimal control scheme is implemented using a derivative-free unconstrained optimization algorithm called NEWUOA (NEW Unconstrained Optimization Algorithm). For illustration, the high-order-harmonic generation (HHG) of a hydrogen atom is considered for optimization. It is shown that optimally shaped laser waveforms can greatly enhance and extend the HHG plateau and efficiently generate an isolated ultrashort attosecond pulse. Moreover, by performing accurate semiclassical simulations and a detailed wavelet time-frequency analysis, we found that the optimized supercontinuum harmonics corresponding to long-trajectory electrons are responsible for an isolated ultrashort 21-as pulse.

No abstract