Compact cryogenic Kerr microscope for time-resolved studies of electron spin transport in microstructures

A compact cryogenic Kerr microscope for operation in the small volume of high-field magnets is described. It is suited for measurements both in Voigt and Faraday configuration. Coupled with a pulsed laser source, the microscope is used to measure the time-resolved Kerr rotation response of semiconductor microstructures with ~1 micron spatial resolution. The microscope was designed to study spin transport, a critical issue in the field of spintronics. It is thus possible to generate spin polarization at a given location on a microstructure and probe it at a different location. The operation of the microscope is demonstrated by time-resolved measurements of micrometer distance diffusion of spin polarized electrons in a GaAs/AlGaAs heterojunction quantum well at 4.2 K and 7 Tesla

Optimisation of Quantum Trajectories Driven by Strong-field Waveforms

Quasi-free field-driven electron trajectories are a key element of strong-field dynamics. Upon recollision with the parent ion, the energy transferred from the field to the electron may be released as attosecond duration XUV emission in the process of high harmonic generation (HHG). The conventional sinusoidal driver fields set limitations on the maximum value of this energy transfer, and it has been predicted that this limit can be significantly exceeded by an appropriately ramped-up cycleshape. Here, we present an experimental realization of such cycle-shaped waveforms and demonstrate control of the HHG process on the single-atom quantum level via attosecond steering of the electron trajectories. With our optimized optical cycles, we boost the field-ionization launching the electron trajectories, increase the subsequent field-to-electron energy transfer, and reduce the trajectory duration. We demonstrate, in realistic experimental conditions, two orders of magnitude enhancement of the generated XUV flux together with an increased spectral cutoff. This application, which is only one example of what can be achieved with cycle-shaped high-field light-waves, has farreaching implications for attosecond spectroscopy and molecular self-probing

Laser wakefield acceleration with mid-IR laser pulses

We report on the first results of laser plasma wakefield acceleration driven by ultrashort mid-infrared laser pulses (\lambda= 3.9 \mu m, 100 fs, 0.25 TW), which enable near- and above-critical density interactions with moderate-density gas jets. Relativistic electron acceleration up to ~12 MeV occurs when the jet width exceeds the threshold scale length for relativistic self-focusing. We present scaling trends in the accelerated beam profiles, charge and spectra, which are supported by particle-in-cell simulations and time-resolved images of the interaction. For similarly scaled conditions, we observe significant increases in accelerated charge compared to previous experiments with near-infrared (\lambda=800 nm) pulses