Coherent control of high-harmonic generation using waveform-synthesized chirped laser fields

We show that waveform-synthesized chirped laser fields are efficient tools for coherent harmonic control. A single harmonic order, or two harmonic orders, can be selectively enhanced by using a two-color field allowing a moderate linear chirp for each color. Different harmonic orders within a wide spectral range can be selectively enhanced by adjusting the laser parameters. Our theory bridges two current harmonic control techniques, namely, single-color phase shaping and multicolor amplitude synthesis, and opens the door to new harmonic control possibilities

Atomic physics of strongly correlated systems

This report discusses: the study of coulombic 3-body systems in hyperspherical coordinates; further studies of electron correlations in doubly excited states of atoms; and theoretical studies of ion-atom collisions

Effects of Ox-LDL on Macrophages NAD(P)H Autofluorescence Changes by Two-photon Microscopy

Ox-LDL uptakes by macrophage play a critical role in the happening of atherosclerosis. Because of its low damage on observed cells and better signal-to- background ratio, two-photon excitation fluorescence microscopy is used to observe NAD(P)H autofluorescence of macrophage under difference cultured conditions- bare cover glass, coated with fibronectin or poly-D-lysine. The results show that the optimal condition is fibronectin coated surface, on which, macrophages profile can be clearly identified on NAD(P)H autofluorescence images collected by two-photon microscopy. Moreover, different morphology and intensities of autofluorescence under different conditions were observed as well. In the future, effects of ox-LDL on macrophages will be investigated by purposed system to research etiology of atherosclerosis.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Electric-dipole matrix-element formulas in hyperspherical coordinates with applications to H\u3csup\u3e-\u3c/sup\u3e and He

Theoretical formulas for the length, velocity, and acceleration forms of the electric-dipole matrix element within the adiabatic hyperspherical coordinate representation are presented. The length and acceleration formulas are used to calculate the photoionization cross section for He up to 1.0 a.u. above threshold and the photodetachment cross section for H- up to 0.35 a.u. above threshold. Length- and acceleration-form results for the dipole oscillator strengths for the discrete He transitions, 1sns(1Se)→1smp(1P0), where n=1, 2, and 3 and m=2, 3, and 4, are also presented. The accuracy of the length- and acceleration-form adiabatic hyperspherical coordinate approximation results is discussed

Universality of returning electron wave packet in high-order harmonic generation with midinfrared laser pulses

We show that a returning electron wave packet in high-order harmonic generation (HHG) with midinfrared laser pulses converges to a universal limit for a laser wavelength above about 3  μm. The results are consistent among the different methods: a numerical solution of the time-dependent Schrödinger equation, the strong-field approximation, and the quantum orbits theory. We further analyze how the contribution from different electron “trajectories” survives the macroscopic propagation in the medium. Our result thus provides a new framework for investigating the wavelength scaling law for the HHG yields

Direct growth of mm-size twisted bilayer graphene by plasma-enhanced chemical vapor deposition

Plasma enhanced chemical vapor deposition (PECVD) techniques have been shown to be an efficient method to achieve single-step synthesis of high-quality monolayer graphene (MLG) without the need of active heating. Here we report PECVD-growth of single-crystalline hexagonal bilayer graphene (BLG) flakes and mm-size BLG films with the interlayer twist angle controlled by the growth parameters. The twist angle has been determined by three experimental approaches, including direct measurement of the relative orientation of crystalline edges between two stacked monolayers by scanning electron microscopy, analysis of the twist angle-dependent Raman spectral characteristics, and measurement of the Moiré period with scanning tunneling microscopy. In mm-sized twisted BLG (tBLG) films, the average twist angle can be controlled from 0° to approximately 20°, and the angular spread for a given growth condition can be limited to < 7°. Different work functions between MLG and BLG have been verified by the Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy. Electrical measurements of back-gated field-effect-transistor devices based on small-angle tBLG samples revealed high-quality electric characteristics at 300 K and insulating temperature dependence down to 100 K. This controlled PECVD-growth of tBLG thus provides an efficient approach to investigate the effect of varying Moiré potentials on tBLG

Imaging an aligned polyatomic molecule with laser-induced electron diffraction

Laser-induced electron diffraction is an evolving tabletop method, which aims to image ultrafast structural changes in gas-phase polyatomic molecules with sub-{\AA}ngstr\"om spatial and femtosecond temporal resolution. Here, we provide the general foundation for the retrieval of multiple bond lengths from a polyatomic molecule by simultaneously measuring the C-C and C-H bond lengths in aligned acetylene. Our approach takes the method beyond the hitherto achieved imaging of simple diatomic molecules and is based upon the combination of a 160 kHz mid-IR few-cycle laser source with full three-dimensional electron-ion coincidence detection. Our technique provides an accessible and robust route towards imaging ultrafast processes in complex gas phase molecules with atto- to femto-second temporal resolution.Comment: 16 pages, 4 figure

Photothermal responsivity of van der Waals material-based nanomechanical resonators

Nanomechanical resonators made from van der Waals materials (vdW NMRs) provide a new tool for sensing absorbed laser power. The photothermal response of vdW NMRs, quantified from the resonant frequency shifts induced by optical absorption, is enhanced when incorporated in a Fabry-Perot (FP) interferometer. Along with the enhancement comes the dependence of the photothermal response on NMR displacement, which lacks investigation. Here, we address the knowledge gap by studying electromotively driven niobium diselenide drumheads fabricated on highly reflective substrates. We use a FP-mediated absorptive heating model to explain the measured variations of the photothermal response. The model predicts a higher magnitude and tuning range of photothermal responses on few-layer and monolayer NbSe$_{2}$ drumheads, which outperform other clamped vdW drum-type NMRs at a laser wavelength of $532\,$nm. Further analysis of the model shows that both the magnitude and tuning range of NbSe$_{2}$ drumheads scale with thickness, establishing a displacement-based framework for building bolometers using FP-mediated vdW NMRs.Comment: 7 pages, 4 figure