Michael G. Schätzel

Attosecond Double-Slit Experiment

A new scheme for a double-slit experiment in the time domain is presented. Phase-stabilized few-cycle laser pulses open one to two windows (slits) of attosecond duration for photoionization. Fringes in the angle-resolved energy spectrum of varying visibility depending on the degree of which-way information are measured. A situation in which one and the same electron encounters a single and a double slit at the same time is observed. The investigation of the fringes makes possible interferometry on the attosecond time scale. From the number of visible fringes, for example, one derives that the slits are extended over about 500 as.

Spatial phase dislocations in femtosecond laser pulses

We show that spatial phase dislocations associated with optical vortices can be embedded in femtosecond laser beams by computer-generated holograms, provided that they are built in a setup compensating for the introduced spatial dispersion of the broad spectrum. We present analytical results describing two possible arrangements: a dispersionless 4f setup and a double-pass grating compressor. Experimental results on the generation of optical vortices in the output beam of a 20 fs Ti:sapphire laser and the proof-of-principle measurements with a broadband-tunable cw Ti:sapphire laser confirm our theoretical predictions.

Non-sequential double ionization in a few-cycle laser pulse: the influence of the carrier–envelope phase

Non-sequential double ionization (NSDI) using phase-stabilised few-cycle laser pulses is investigated. We report differential measurements of Ar ++ ion momentum distributions. They show a strong dependence on the carrier-envelope (CE) phase. Via control over the CE phase one is able to direct the NSDI dynamics. Data analysis through a classical model calculation reveals that the influence of the optical phase enters via: (1) the cycle-dependent electric field ionization rate, (2) the electron recollision time and (3) the accessible phase space for inelastic collisions. Our model indicates that the combination of these effects allows a look into single-cycle dynamics already for few-cycle pulses.

Spatiotemporal determination of the absolute phase of few-cycle laser pulses

We determined the carrier-envelope (“absolute”) phase of linearly polarized few-cycle laser pulses by measuring the energy-resolved asymmetry of electron emission from noble gases. The Gouy phase shift in the laser focus is also measured, providing the first full spatiotemporal depiction of the electric field in the whole focal region.