Strong-field Spectroscopy with Multicolor Pulses - Project 03

Project Leader: Andrius Baltuska

Electric field strengths required to free electrons from a binding potential in atoms, molecules and solids are easily achieved in femtosecond light pulses emitted by modern laser amplifiers and optical parametric amplifiers. The strong-field regime provides straightforward access to attosecond control over electron emission because electron liberation is temporally localized to a narrow fraction of an optical cycle, particularly when the ionization mechanism is dominated by tunneling. The best-known example of sub-cycle electron emission control is the generation of attosecond bursts of coherent XUV radiation - high-order harmonic generation (HHG) - occurring upon the electron recombination with the parent ion. Intra-cycle control of the generation of free charge carriers in transparent bulk solids opens an intriguing avenue toward creating new transient properties in materials and, therefore, presents a fascinating exploration route toward much faster - potentially 1014 Hz - optoelectronic devices. In this project within the SFB, we will experimentally study the possibility to create a transient metallic response in bulk dielectrics and in nanometer-scale dielectrics.

One aim is to exploit the optical signature of the tunneling current that exhibits twice-per-cycle periodicity and, when probed by optical light, creates a transient optical response. In 2010, we conducted a proof-of-principle experiment to confirm the existence of this phenomenon using a single-color excitation. Within the proposed SFB, we will take advantage of state-of-the art few-cycle IR parametric amplifiers that, on the one hand, permit us to reach a predominantly tunneling ionization regime and, on the other hand, provide a platform for multicolor optical pulse shaping which should result in a much better resolved temporal and spatial localization of the effect.

The other major aim of the project is to exploit the possibility to enhance a strong-field interaction - such as HHG and THz wave emission of plasma micro-currents - by introducing nanoparticles into a gaseous target. The near-term objective within this project is to explore the applicability limits of nano-localized attosecod currents created in bulk solids and gases by tailored optical strong fields. The longterm perspective is to apply such sophisticated attosecond control to increasingly more complex targets, such as various nano-objects and large polyatomic molecules with strongly correlated electrons.

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