Time delays in (w; 2w) above threshold ionization

LÓPEZ, S. D.; ARBÓ, D. G.; DONSA, S.; J. BURGDÖRFER; S NAGELE

Barcelona

Conferencia; 26th International Conference on Atomic Physics, ICAP 2018; 2018

Experiments employing either attosecond streakingor the complementary interferometric RABBITtechnique have allowed to study photoemission fromrare gas atoms and surfaces in the time-domain withattosecond precision. The experimental progress hastriggered considerable theoretical eorts to understandphotoionization from a time-dependent perspective(see [1] and references therein).The experiment in atomic ionization by two-color(!; 2!) lasers by Zipp et al. [2] has revealed thata pump-probe scheme can be used to characterizetime delays in the emission of electrons in the abovethresholdionization regime for visible frequency ofthe pump. In this work, we perform a theoreticalanalysis of the time delays in Ar ionization by twocolorlaser for a typically (!; 2!) conguration ofTi:sapphire laser (800 nm). To shed more light inionization process we perform simulations with thetime dependent Schrodinger equation and comparethis results with the strong eld and Coulomb-Volkovapproximations. We nd that time delays depend onthe denition from electron momentum distributions.Besides, we also nd a large discrepancy between theresults predicted by the strong eld approximation(zero delay for sidebands) and numerical solutions oftime-dependent Schrodinger equation at the highestsimulation energies. We also nd that the strong assumptionof additive time delays adopted in streakingor RABBITT techniques [3] needs to be revisitedwhen applied to the case of (!; 2!) lasers due to themultiplicity of coherent quantum paths leading to anal multiphoton peak. Finally, we explore simplerquantum paths to get a better understanding of theprocess. For this purpose we use Yukawa potentialstting the electron binding energy to allow the absorptionof a desired number of photons to reach thecontinuum. This analysis paves the way to understandthe process and the time delays asociated toeach path.As an example, we show in Fig. 1 time delays obtainedfrom asymmetries and forward emission, consideringintegrations over z hemispheres. This isdone for a single energy calculated from energy conservation,or by integrating in energy around thepeak.This work was supported by the FWF-Austria(SFB NEXTLITE, SFB VICOM), by CONICET(PIP100386), by ANPCYT (PICT-2016-0296 andPICT-2016-3029), by the OeAD (WTZ AR 03/2013),Figure 1: Delays calculated as a function of the emissionenergy for sidebands within the TDSE. The delays arecalculated for forward emission (triangles) and asymme-try (circles). The calculations were performed integrat-ing around peak energy (solid symbols) or consideringonly the peak energy (open symbols). The 2! compo-nent intensity is 81013 W/cm2 and the ! component is41011 W/cm2.by the NSF through XSEDE resources (TGPHY090031),and through computational resourcesat the Vienna Scientic Cluster (VSC).[1] R. Pazourek, S. Nagele, and J. Burgdorfer, Rev.of Mod. Phys., (2015), 87, 765 .[2] L. J. Zipp, A. Natan, and P. H. Bucksbaum,Optica, (2014) 1, 361-364.[3] J. Feist, O. Zatsarinny, S. Nagele, R. Pazourek,J. Burgdorfer, X. Guan, K. Bartschat and B. I.Schneider, Phys. Rev. A, (2014), 89, 033417.