arXiv subjects

Lorenzo Colaizzi

Publications and source records attributed to Lorenzo Colaizzi.

2 recordsLinked to original sources

arXiv2025

Engineering High-Order Harmonic Generation through Gas Confinement at Sub-Millimeter Lengths

Attosecond light sources based on high-order harmonic generation (HHG) constitute to date the only table-top solution for producing coherent broadband radiation covering the spectral range from the extreme ultraviolet to the soft X-rays. The so-called emission cutoff can be extended towards higher photon energies by increasing the driving wavelength at the expense of conversion efficiency. An alternative route is to overdrive the process by using higher laser intensities, with the challenging requirement of interacting with higher plasma densities over short propagation distances. Here, we address this challenge by using a differentially pumped glass chip designed for optimal gas confinement over sub-mm lengths. By driving HHG with multicycle pulses at either 800 nm or 1500 nm, we demonstrate a cutoff extension by a factor of two compared to conventional phase matching approaches and surpassing the present record using multicycle fields. Our three-dimensional propagation simulations, in excellent agreement with the experiment, confirm that gas confinement is crucial since efficient phase matching of cutoff harmonics occurs only for short propagation lengths. Additionally, we show that the high photon energy component is not only temporally confined to the leading edge of the driving pulse, but also spatially confined in the near-field to an off-axis contribution due to reshaping of the driving field along propagation inside the medium. Our findings contribute to the fundamental understanding of HHG across different regimes.

physics.optics↗

arXiv2024

Capturing electron-driven chiral dynamics in UV-excited molecules

Molecular chirality is a key design property for many technologies including bioresponsive imaging, circularly polarized light detection and emission, molecular motors and switches. Imaging and manipulating the primary steps of transient chirality is therefore central for controlling numerous physical, chemical and biological properties that arise from chiral molecules in response to external stimuli. So far, the manifestation of electron-driven chiral dynamics in neutral molecules has not been demonstrated at their intrinsic timescale. Here, we use time-resolved photoelectron circular dichroism (TR-PECD) with an unprecedented instrument response function of 2.9 fs to image the dynamics of coherent electronic motion activated by prompt UV-excitation in neutral chiral molecules, disclosing its impact on the molecular chiral response. We find that electronic beatings between Rydberg states lead to periodic modulations of the chiroptical response on the few-femtosecond timescale, showing a sign inversion in less than 10 fs. Calculations including both the molecular UV-excitation and subsequent photoionization confirm this interpretation and provide further evidence that the combination of the resulting photoinduced chiral current with a circularly polarized probe pulse realizes an enantio-selective filter of molecular orientations upon photoionization, opening up a route towards enantio-selective charge-directed reactivity.

physics.chem-ph↗