Project Details
Projekt
Spatio-Temporal Tailoring of Light Fields for Sub-Cycle Resolved Measurements of Strong-Field Effects
Applicant
Dr. Adrian Pfeiffer
Subject Area
Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
Term
from 2015 to 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 281272215
Laser pulses with durations short enough to probe the electronic timescale can be generated in the XUV and in the IR-VIS regime. High-order harmonic generation can be used to generate isolated attosecond pulses and pulse trains in the XUV, and since very recently coherent synthesis of optical pulses is used to generate subcycle optical waveforms in the IR-VIS regime. At photon energies in the regime 5-15 eV, pulses with such extremely short durations have not yet been demonstrated. Frequency conversion in a gas cell or filamentation yields comparatively short pulses, but the complex interplay of nonlinear light-matter interaction and significant linear dispersion has prevented to approach the femtosecond barrier. For spectroscopic applications, such as transient absorption spectroscopy, broadband and sub-femtosecond pulses in the UV/VUV would be very useful, because they allow the direct probing of the bandgap in many materials. The central quest of this project is to investigate the generation of UV/VUV fields in solid targets by femtosecond NIR pulses in a non-collinear geometry. Using thin bulk solids (thickness 15-100 µm) as generation media, cascaded processes of low-order harmonic generation and self-diffraction yield a multifaceted emission pattern in the UV/VUV. A specially designed spectrometer records the emission pattern in the bisector of the generating pulses and beyond, and interferences in the UV/VUV field are used to scrutinize the nonlinear light-matter interaction. The goal of the experimental methods is to track changes in the band structure and/or population dynamics in the transition regime between perturbative and strong-field optics. The generation of short UV/VUV pulses can be optimized in the noncollinear geometry, and < 2 fs-pulses can be generated at selected emission angles. Using circularly polarized counter-rotating generation pulses, fields in the UV/VUV with varying ellipticity can be achieved. A generic feature is that the UV/VUV pulses are separated from the fundamental field through the noncollinear geometry, which is especially beneficial in a regime where thin metal filters cannot be used for the separation from the fundamental pulses. The generated UV/VUV pulses cannot be used in traditional pump-probe experiments, because they have very low intensity and they exist only as tailored fields with spatiotemporal couplings behind the generation medium, preventing beam transport or refocusing. However, they can be utilized in transient absorption experiments when a probe sample is located directly after the generation sample.
DFG Programme
Priority Programmes
