RESUMO
Nanoplasmas induced by intense laser fields have attracted enormous attention due to their accompanied spectacular physical phenomena which are vigorously expected by the community of science and industry. For instance, the energetic electrons and ions produced in laser-driven nanoplasmas are significant for the development of compact beam sources. Nevertheless, effective confinement on the propagating charged particles, which was realized through magnetic field modulation and target structure design in big facilities, are largely absent in the microscopic regime. Here we introduce a reliable scheme to provide control on the emission direction of protons generated from surface ionization in gold nanoparticles driven by intense femtosecond laser fields. The ionization level of the nanosystem provides us a knob to manipulate the characteristics of the collective proton emission. The most probable emission direction can be precisely steered by tuning the excitation strength of the laser pulses. This work opens new avenue for controlling the ion emission in nanoplasmas and can vigorously promote the fields such as development of on-chip beam sources at micro-/nano-scales.
RESUMO
The near-field enhancement effect in nanoparticles dominates the dynamical response of the atoms and molecules within the nanosystem when interacting with ultrashort laser pulses. In this work, using the single-shot velocity map imaging technique, the angle-resolved momentum distributions of the ionization products from surface molecules in gold nanocubes have been obtained. The far-field momentum distributions of the H+ ions can be linked with the near field profiles demonstrated by a classical simulation considering the initial ionization probability and the Coulomb interactions among the charged particles. This research provides an approach to look at the nanoscale near field distribution in the extreme interactions of femtosecond laser pulses and nanoparticles, paving the way for exploring the complex dynamics.
RESUMO
We report the ionization reduction of atoms in two-color femtosecond laser fields in this joint theoretical-experimental study. For the multiphoton ionization of atoms using a 400 nm laser pulse, the ionization probability is reduced if another relatively weak 800 nm laser pulse is overlapped. Such ionization reduction consistently occurs regardless of the relative phase between the two pulses. The time-dependent Schrödinger equation simulation results indicate that with the assisted 800 nm photons the electron can be launched to Rydberg states with large angular quantum numbers, which stand off the nuclei and thus are hard to be freed in the multiphoton regime. This mechanism works for hydrogen, helium, and probably some other atoms if two-color laser fields are properly tuned.
RESUMO
The complete mitochondrial genome of Trichogaster leeri is determined in this study. It is 16,454 bp in length and consists of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and a non-coding control region (D-loop). The overall base composition of the heavy-strand (H-strand) of the T. trichopterus mitochondrial genome is A: 29.18%, T: 28.07%, C: 27.20% and G: 15.55%. The total length of the 13 protein-coding genes was 11,435 bp. Phylogenetic analysis showed that the species of Trichogaster (T. trichopterus, T. lalius and T. leeri) formed a monophyletic group and represented close relationship with the species of Anabantoidei. This study provides an important data set for phylogenetic and taxonomic analyses of the species of genus Trichogaster.
