Alexander Mitrofanov

Strong-field plasmonic electron acceleration with few-cycle, phase-stabilized laser pulses

We carried out experimental investigations on surface plasmon enhanced electron acceleration with few-cycle, carrier-envelope phase (CEP) stabilized laser pulses. We determined the spectrum of electrons accelerated in the plasmonic field and found that signatures of the phase stabilized optical waveform driving the individual electron trajectories are washed out in the electron spectra. We attribute this effect to nanoscale surface roughness of the metallic samples, as supported by extensive numerical simulations. This finding explains the previously observed, low CEP sensitivity of photoemission processes from metallic films and enables the development of femtosecond electron sources for ultrafast time-resolved applications.

Observation of few-cycle, strong-field phenomena in surface plasmon fields

We present experimental evidence of the generation of few-cycle propagating surface plasmon polariton (SPP) wavepackets. Ultrashort plasmonic pulses were generated by few-cycle laser pulses of 5.5 fs to 6.5 fs duration on a thin silver film of 50 nm thickness coated on the face of a right-angle prism to enable Kretschmann-type SPP coupling. SPP pulses were characterized by an autocorrelation-type measurement based on fourth order, nonlinear electron photoemission induced by the SPP field. The evaluation of the measured ultrashort, fringe-resolved autocorrelation curve of the SPP wavepacket (Fig. 1a) resulted in a retrieved SPP pulse length of 6.5 fs, as evidenced by the reconstructed curve in Fig. 1b. This first demonstration of the generation of few-cycle propagating SPP wavepackets on a metal surface has important applications in ultrafast plasmonics.

Time-and-energy-resolved measurement of Auger cascades following Kr 3d excitation by attosecond pulses

We show that attosecond metrology has evolved from proof-of- principle experiments to a level where complex processes can be resolved in time that cannot be accessed using any other existing technique. The cascaded Auger decay following ionization and excitation of the 3d-subshell in Kr with subfemtosecond 94eV soft x-ray pulses has been energy- and time-resolved in an x-ray pump-infrared probe experiment. This Auger cascade reveals rich multi- electron dynamics, which despite the fact that there are many experimental and theoretical data available, is not yet fully understood. We present time-resolved data showing the sequence of the temporal dynamics in the cascaded Auger

Plasma-blueshift spectral shear interferometry for characterization of ultimately short optical pulses

We introduce a bandwidth-unlimited, dispersion- and shear-self-calibrated, timing-jitter-free pulse measurement technique based on a quasi-linear temporal phase modulation in a gas weakly ionized by a long pump pulse. Results of a 5 fs pulse characterization are reported.

Time-and-energy resolved measurement of the cascaded Auger decay in krypton

The cascaded Auger decay following ionization or excitation with 94 eV soft-X-ray pulses from the 3d subshell in krypton has been energy-and-time-resolved for the first time. The decay time of the 4s−14p−2nl → 4p−3 + e and/or 4s−14p−1nl → 4p−2 + e transition is measured to be 74 ± 20 fs. Furthermore, our data shows that the electrons with a kinetic energy around 25 eV (generally assigned as 3d−1np → 4s−2n′p + e) emitted after core excitation are emitted in a second decay step suggesting an alternative assignment of the form 4s−2np 4p−2 + e.

Optical Mapping of Attosecond Ionization Dynamics by Few-Cycle Light Pulses

Few-cycle light pulses are used to map ultrafast ionization dynamics in the time and frequency domain by all-optical means. Tunneling ionization encodes an attosecond phase mask, suggesting a promising method for attosecond shaping of high-intensity optical fields.

13mJ sub-three optical cycle 3.9-um pulses through hollow-core-waveguide compression

Few-cycle high peak power mid-IR sources are required for strong field applications, such as driving HHG in the keV range [1] and high efficiency THz generation [2]. In order to expose target to a peak field without causing excessive ionization, ultrashort pulses consisting of a few-cycles are needed. Parametric sources based on KTA crystals have been successfully used for the generation of multi-mJ pulses in the 3–4 μm range [3], however, the duration is typically limited to sub-100 fs duration due to phase matching bandwidth limitations. A robust and popular scheme for the generation of few-cycle pulses is via post-compression in a hollow core fiber (HCF) filled with noble gas [4] that yields uniform pulse compression across the beam and the perfect beam profile at the output due to spatial filtering effects.

Hollow-Core-Waveguide Compression of 22-mJ 3.9-µm Pulses

We present post-compression of 22-mJ 90-fs pulses at 3.9 µm via spectralbroadening in a noble-gas-filled 1 mm core diameter 3 meter long capillary with over 60% throughput and recompressed in a bulk BaF2 plate down to 33 fs.

Strong Field Ionization in a Multi-color Field

We describe several implementations of multi-color shaping of the optical cycles of intense laser pulses, which allow direct control of strong-field dynamics and have important implications for many of their applications. After reviewing a purely optical detection method for attosecond tunneling ionization bursts in gases and transparent solids, we experimentally demonstrate the steering of the induced tunneling electron current via the optical cycle shape of the driving laser pulses. We describe two examples: the control of the electron emission direction in above-threshold ionization, and a new scheme for the efficient generation of tunable THz radiation. Finally, we also describe an application of shaped optical cycles to the generation of ultrafast XUV pulses and present first results on steering of the returning electron trajectories in HHG.

Sub-cycle time-resolved single photon ionization

With the availability of coherent isolated attosecond XUV pulses, a wide range of experiments has become feasible, ranging from direct measurement of the vector potential of a light field [1] to the observation of interference between bound and free electron wave packets [2] and the time-resolved measurement of cascaded Auger decays [3]. In this work, we observe the interference of electron wave-packets generated through direct photo-ionization and electron wave-packets generated through an Auger decay following XUV excitation of Krypton. The reference free electron wave packet opens the possibility to retrieve phase information about the Auger wavepacket, which can not be retrieved from the streaking alone.