arXiv subjects

Angela Vella

Publications and source records attributed to Angela Vella.

4 recordsLinked to original sources

arXiv2026

A Compact High-Repetition-Rate Intense THz Source for Atomic-Scale Materials Characterization

High-intensity terahertz (THz) sources combining high repetition rates, strong field amplitudes, and long-term stability are key enabling technologies for next-generation ultrafast photonics. However, simultaneously achieving these characteristics in a compact and practical architecture remains a major challenge. Here, we report a high-performance tabletop THz source delivering intense single-cycle pulses at 100 kHz, generated by optical rectification in lithium niobate using an optimized echelon-based tilted-pulse-front scheme and driven by an industrial-grade ytterbium laser. The source achieves optical-to-THz conversion efficiencies exceeding 0.13% at room temperature, peak electric fields of several hundred kV/cm, and excellent long-term stability, establishing a robust platform for high-average-power strong-field THz applications. As a proof of concept, the source was integrated into an atom probe tomography (APT) instrument. APT reconstructs the three-dimensional chemical composition of materials through field-induced ion emission from a sharp nanotip. While THz-assisted ion emission has been shown to improve analytical performance by reducing thermal effects, previous demonstrations were limited to low-repetition-rate THz sources, restricting throughput and accessible analysis volumes. Using an aluminum nanotip, we demonstrate efficient THz-assisted APT at 100 kHz and benchmark its performance against conventional voltage- and laser-assisted operation. The high repetition rate enables rapid large-volume acquisition while improving mass resolving power, reducing thermal tailing, and preserving high-quality three-dimensional reconstructions. Beyond APT, this work establishes a compact and scalable high-repetition-rate THz platform for strong-field physics, nonlinear THz photonics, ultrafast spectroscopy, and material characterization at the nanoscale.

cond-mat.mtrl-sci↗

arXiv2025

Role of defects in atom probe analysis of sol-gel silica

Silicon dioxide is a suitable material to encapsulate proteins at room temperature so that they can be analysed at the atomic level using laser-assisted atom probe tomography (La-APT). To achieve this goal, in this study we show that UV and deep UV lasers can achieve a high success rate in La-APT of silica in terms of chemical resolution and three-dimensional image volume, with both lasers providing comparable results. Since the La-APT analyses are driven by photon absorption, in order to understand the mechanisms behind the enhanced absorption of UV light, we performed density functional theory calculations to model the electronic and optical properties of amorphous silica matrices generated using a Monte Carlo approach to structural optimisation. In particular, we have investigated the role of various defects introduced during sample preparation, such as substitutional and interstitial carbon, sodium and gallium ions, and hydrogen. Our results show that the presence of defects increases the absorption of silica in the UV and deep-UV range and thus improves the La-APT capabilities of the material. However, due to the low density of free charge carriers resulting from the absorption of laser energy by defects, deviations from the nominal chemical composition and suboptimal chemical resolution may occur, potentially limiting the optimal acquisition of APT mass spectra.

cond-mat.mtrl-sci↗

arXiv2024

Evaporation of cations from non-conductive nano-samples using single-cycle THz pulses: an experimental and theoretical study

This study investigates the emission of cations from silica samples by single-cycle THz pulses, focusing on the influence of pulse polarity. Negative THz pulses were found to efficiently trigger the evaporation of cations from nanoneedles in amorphous silica samples compared to positive pulses. Conversely, this dependence on pulse polarity could not be found in samples with metallic behaviour such as LaB$_6$ and when multi-cycle pulses in different frequency ranges such as ultraviolet (UV) are used. First-principles simulations focus on silica under THz laser irradiation and show critical fields for ion evaporation of hydroxyl groups from Si(OH)$_4$, which serves as a model precursor molecule for the amorphous solid matrix. To explain our experimental results, we propose a simplified theoretical model that determines the role of the polarity of the THz pulse by taking into account the differences in electron mobility between silica and semi-metallic samples. The study explores the nonlinear microscopic mechanisms of atomic evaporation under external static and THz laser fields and clarifies the dynamics of THz-enhanced APT and related applications.

cond-mat.mtrl-sci↗

arXiv2020

A Photonic Atom Probe coupling 3D Atomic Scale Analysis with in situ Photoluminescence Spectroscopy

Laser enhanced field evaporation of surface atoms in Laser-assisted Atom Probe Tomography (La-APT) can simultaneously excite phtotoluminescence in semiconductor or insulating specimens. An atom probe equipped with appropriate focalization and collection optics has been coupled with an in-situ micro-Photoluminescence (μPL) bench that can be operated during APT analysis. The Photonic Atom Probe instrument we have developped operates at frequencies up to 500 kHz and is controlled by 150 fs laser pulses tunable in energy in a large spectral range (spanning from deep UV to near IR). Micro-PL spectroscopy is performed using a 320 mm focal length spectrometer equipped with a CCD camera for time-integrated and with a streak camera for time-resolved acquisitions. An exemple of application of this instrument on a multi-quantum well oxide heterostructure sample illustrates the potential of this new generation of tomographic atom probe.

physics.app-ph↗