Non-constant ponderomotive energy in above threshold ionization by intense few-cycle laser pulses

R. DELLA PICCA; GRAMAJO, A. A.; ARBÓ, D. G.; LÓPEZ, S. D.; C. R. GARIBOTTI

Toledo

Conferencia; XXIX International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC2015); 2015

Universidad Autónoma de Madrid, Consejo Superior de Investigaciones Científicas y La Asociación para la Promoción de la Química Teórica y Computacional

We analyze the contribution of the quiver kinetic energy acquired by anelectron in an oscillating electric field to the energy balance inatomic ionization processes by a short laser pulse. Due to the timedependence of this additional kinetic energy, a temporal average isassumed to maintain a stationary energy conservation rule. This rule isused to predict the position of the peaks observed in the photo electronspectra (PE). For a flat top pulse envelope, the mean value of thequiver energy over the whole pulse leads to the concept of ponderomotiveenergy $U_{p}$. However for a short pulse with a fast changing fieldintensity a stationarity approximation could not be precise. We checkthese concepts by studying first the photoelectron (PE) spectrum withinthe Semiclassical Model (SCM) for a multiple steps pulses. The SCMoffers the possibility to establish a connection between emission timesand the PE spectrum in the energy domain. We show that PE substructuresstem from ionization at different times mapping the pulse envelope. Wealso present the analysis of the PE spectrum for a realisticsine-squared envelope within the Coulomb-Volkov and \textit{ab initio}calculations solving the time-dependent Schr\"odinger equation. We foundthat the electron emission amplitudes produced at different timesinterfere with each other and produce a new additional pattern, thatoverlap the above-threshold ionization (ATI) peaks.