Today laser pulses with electric fields comparable to or higher than the electrostatic forces binding valence electrons in atoms and molecules have become a routine tool applications acceleration of ions, generation short wavelength emission from plasmas clusters, fusion, etc. Intense are also naturally created during filamentation air due local field enhancements vicinity metal nanoparticles. One would expect that very intense always lead fast ionization molecules. However, recently...

In standard lasers, light amplification requires population inversion between an upper and a lower state to break the reciprocity absorption stimulated emission. However, in medium prepared specific superposition state, quantum interference may fully suppress while leaving emission intact, opening possibility of lasing without inversion. Here we show that arises naturally during propagation intense femtosecond laser pulses air. It is triggered by combination molecular ionization alignment,...

We discuss the connection between strong-field ionization, saturation of Kerr response and formation Kramers–Henneberger (KH) atom long-living excitations in intense infrared (IR) external fields. present a generalized model for intensity-dependent atoms strong IR laser fields, describing deviations nonlinear at frequency driving field from standard model. show that shaping pulse allows one to reveal signatures excited KH states an individual atom.

Air lasing from single ionized N_{2}^{+} molecules induced by laser filamentation in air has been intensively investigated and the mechanisms responsible for are currently highly debated. We use ultrafast nitrogen K-edge spectroscopy to follow strong field ionization fragmentation dynamics of N_{2} upon interaction with an ultrashort 800 nm pulse. Using probe pulses generated extreme high-order harmonic generation, we observe transitions indicative formation electronic ground X^{2}Σ_{g}^{+},...

Interaction of a laser pulse with centrally symmetric medium, such as an isotropic gas atoms, leads to the generation harmonic emission which contains exclusively odd harmonics incident field. This result is consequence both central symmetry medium and temporal oscillating electric field, , where ωl frequency. In case oriented heteronuclear molecules, spatial no longer holds even become allowed. Here we show, by solving time-dependent Schrödinger equation for H, D, T, that even-order also...

Nonadiabatic processes play a fundamental role in the understanding of photochemical excited polyatomic molecules. A particularly important example is that radiationless electronic relaxation at conical intersections (CIs). We discuss new opportunities for controlling coupled electron–nuclear dynamics CIs, offered by advent nearly single-cycle, phase-stable, mid-infrared laser pulses. To illustrate control mechanism, two-dimensional model NO2 molecule considered. The key idea scheme to match...

Air lasing in the nitrogen molecular ion is not well understood because complex physics responsible for gain interwoven with pulse propagation an extreme environment. Here we use a short gas jet to limit interaction length, thereby removing effects. We report on several mechanisms that contribute decay of different conditions, and experimentally isolate two timescales: long-term due collisional state mixing, short-term cannot be explained by population inversion. To test former, control...

The choice of the most suitable analytic photoionization model in solids is a challenging task with no default solution. Here we show how best formalism can be determined based on waveform pulse reflected by sample due to photoionized almost-free electrons conduction band. For typical case diamond, compare three simple models and benchmark them against highly accurate first-principle TDDFT simulation, analysing fit between pulses time frequency domain. aims this paper, have developed...

We simulate the pump-probe experiments of lasing in molecular nitrogen ions with particular interest effects rotational wave-packet dynamics. Our computations demonstrate that coherent preparation wave packets ${\mathrm{N}}_{2}{}^{+}$ by an intense short nonresonant pulse results a modulation subsequent emission from ${B}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Sigma}}}_{u}{}^{+}\ensuremath{\rightarrow}{X}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$...

Time-resolving and controlling coupled electronic nuclear dynamics at conical intersections on the sub-femtosecond to few-femtosecond time scale is among challenging goals of attosecond physics. Here we present numerical simulations time-resolved photoelectron spectroscopy such in NO2, where electron-nuclear motion 2A1/2B2 intersection steered sub-laser-cycle by a nearly single-cycle, waveform controlled mid-infrared laser pulse. For rigorous description photoionization dynamics, employ ab...

We provide a unified concept for understanding and imaging excited state dynamics in atoms molecules intense laser fields, including microscopic description of high order Kerr non-linearities their role filamentation.

We present a generalized model for the intensity dependent response of atoms in strong IR laser fields, describing deviations nonlinear at frequency driving field from standard (linear Kerr effect + plasma defocusing) based on formation stable KH states. According to our numerical simulations, shaping pulse allows one reveal prominent resonance structure an individual atom, which can only be explained by population transfer into excited

In standard lasers, light amplification requires population inversion between an upper and a lower state to break the reciprocity absorption stimulated emission. However, in medium prepared specific superposition state, quantum interference may fully suppress while leaving emission intact, opening possibility of lasing without (LWI) [1] . Conventional LWI schemes generally strive maintain phase relationship lower-lying states that carry most population. We present scheme [2] , [3] does not...

The dissociative excitation of CO was studied in the molecular frame as a function probe laser intensity, ellipticity and polarization with respect to bond at wavelengths 800 nm 1350 nm. This allowed identification main pathway consisting tunnel ionization from HOMO-2 followed by parallel dipole transition second excited state B predissociating, third C. Recollision shown play negligible role. Using induced impulsive alignment, strong field coupling ionic states C could thus be controlled...

Using the example of molecular ion and its isotopes, we show how Coulomb explosion triggered by ionization molecule can be used to reconstruct emission times identify physical mechanism contributing near- below-threshold harmonics (BTH). The key idea is that recombination responsible for harmonic halts at different times, depending on final vibrational state molecule. As a consequence, interferences between channels up, enabling enhanced temporal resolution in spectrum. reconstruction BTH...

It is commonly assumed that for low-intensity short optical pulses far from resonance, the third-order nonlinear response instantaneous. We solve three-dimensional time-dependent Schrödinger equation hydrogen atom and show this not case: polarization simply proportional to cube of electric field even at low intensities. analyze fundamental-frequency third-harmonic susceptibilities hydrogen, investigate their dependence on intensity, find delays in Kerr rapidly approach femtosecond time-scale...

Summary form only given. Inducing and controlling lasing in the open air is an intriguing challenge. Several recent experiments on laser filamentation have demonstrated generation of population inversion at 391 nm 428 lines nitrogen molecular ion [1-8], corresponding to transitions between ground vibrational state second excited electronic state, B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Σ <sub...

We establish a first-principle model for the simulation of spatiotemporal light pulse dynamics based on combination time-dependent Schrödinger equation and unidirectional propagation equation. The proposed numerical scheme enables computationally efficient while being stable accurate. use new to examine self-focusing short in atomic hydrogen show that an accurate description excited-levels can only be achieved by with ab-initio light-matter interaction, which accounts laser-dressed...

Views Icon Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Twitter Facebook Reddit LinkedIn Tools Reprints and Permissions Cite Search Site Citation Olivier Heckmann, Maria Christine Richter, Jean-Michel Mariot, Laurent Nicolaï, Ivana Vobornik, Weimin Wang, Uros Djukic, Karol Hricovini; Quasi 1D structures at the Bi/InAs(100) surface. AIP Conf. Proc. 1 August 2018; 1996 (1): 020017. https://doi.org/10.1063/1.5048869 Download citation file: Ris (Zotero)...

We show that lasing without inversion arises naturally during propagation of intense femtosecond laser pulses in air. It is triggered by the combination molecular ionization and alignment, both unavoidable light fields.

We discuss the connection between strong-field ionization, saturation of Kerr response, and formation Kramers-Henneberger (KH) atom long-living excitations in intense external fields.