INTRACYCLE INTERFERENCE IN ABOVE PHOTOIONIZATION

D. G. ARBÓ; K. L. ISHIKAWA; K. SCHIESSL; E. PERSSON; J. BURGDÖRFER

Salamanca, España

Conferencia; 10th European Conference on Atoms, Molecules and Photons; 2010

We study interference effects observed in the electron yield of atomic ionization due to the interaction with linearly polarized high intensity laser pulses [1]. The dependence on the carrier frequency is systematically investigated. The interplay between intra- and intercycle interferences of electron trajectories leads to modulations in the photoelectron spectra. Intercycle interference corresponds to the well-known ATI peaks of the photoelectron spectrum arising from the superposition of wave packets of different optical cycles, whereas intracycle interference comes from the coherent superposition of electron wave packets released within the same optical cycle. The latter corresponds to a diffraction grating in the time domain [1,2]. In Fig. 1 we display the two dimensional interferogram, i.e energy spectra (expressed as continuous ATI order n) as a function of carrier wavelength l, calculated by numerically solving the time-dependent Schrödinger equation. The intercycle interference pattern can be seen as horizontal stripes close to entire values of n, and is modulated by the intracycle interference observed as oblique stripes. The intracycle interference modulation is independent of the total number of optical cycles involved in the laser pulse and is affected by the long-range nature of the atomic potential. A simple semiclassical model (not shown) explains the calculated patterns. Within the semiclassical model we derive an analytical expression for the separation of intracycle peaks showing an excellent agreement with the exact quantum calculations (Fig. 2).Intercycle interference corresponds to the well-known ATI peaks of the photoelectron spectrum arising from the superposition of wave packets of different optical cycles, whereas intracycle interference comes from the coherent superposition of electron wave packets released within the same optical cycle. The latter corresponds to a diffraction grating in the time domain [1,2]. In Fig. 1 we display the two dimensional interferogram, i.e energy spectra (expressed as continuous ATI order n) as a function of carrier wavelength l, calculated by numerically solving the time-dependent Schrödinger equation. The intercycle interference pattern can be seen as horizontal stripes close to entire values of n, and is modulated by the intracycle interference observed as oblique stripes. The intracycle interference modulation is independent of the total number of optical cycles involved in the laser pulse and is affected by the long-range nature of the atomic potential. A simple semiclassical model (not shown) explains the calculated patterns. Within the semiclassical model we derive an analytical expression for the separation of intracycle peaks showing an excellent agreement with the exact quantum calculations (Fig. 2).