Single-cycle terahertz (THz)-assisted atom probe tomography (APT) has emerged as a promising technique for triggering field evaporation under conditions that may reduce thermally activated contributions compared with conventional laser pulsing in conductive materials. While free carriers in metallic samples facilitate efficient THz near-field coupling at the specimen apex, nonmetallic materials like sol-gel silica lack this advantage, rendering positive THz pulses ineffective. However, negative THz pulses produce well-resolved mass spectra, which are compared with the mass spectra obtained with laser assisted APT( UV 343 nm and NIR 800 nm) to evaluate mass resolving power, signal-to-noise ratio and chemical composition. Moreover, we study the impact of the coating on the THz-APT results. Two metallization strategies are applied: (i) chromium (Cr) sputter coating via PECS and (ii) graphene encapsulation. Cr coating enables successful ion evaporation under positive THz pulses, improving mass resolution and reducing noise, while graphene encapsulation further enhances spectral clarity by sharpening peaks and reducing thermal tails. 3D reconstructions confirm effective deposition of both coatings over the tungsten-silica junction and reveal species segregation under positive THz pulses, highlighting the strong dependence of evaporation behavior on the applied field conditions.

Monazite (CePO4) is widely used in U-Th-Pb geochronology due to its reliable age determinations, although isotopic disturbances often require investigation at the nanoscale to better understand the mechanisms at play. Atom probe tomography (APT) offers unique capabilities for nanoscale chemical analysis and 3D atomic reconstruction but presents challenges for insulating materials such as CePO4, particularly due to oxygen loss during field evaporation. This study investigates the effects of laser wavelength, energy, metallic coatings, and detection device on mass spectrum optimization and compositional accuracy in synthetic CePO4 samples. Results show that shorter laser wavelengths (260 nm) enhance peak resolution, particularly when combined with advanced reflectron configurations, as demonstrated with the LEAP 6000 XR. Chromium coatings further improve thermal dissipation and reduce noise levels. However, compositional measurements reveal systematic underestimation of oxygen and overestimation of P and Ce, likely influenced by preferential low-field evaporation of certain elements. These findings highlight the need to carefully tune experimental parameters to mitigate quantification biases and enhance the reliability of APT analyses for geological materials.

Terahertz optics enables powerful spectroscopy and imaging thanks to its non-ionizing nature and sensitivity to molecular and material properties. It is also beneficial to next-generation communications, since it offers vast bandwidth for ultra-fast, low-latency data transfer. Polarization control of terahertz waves is vital for applications in chiral zation control-particularly for ultra-broadband terahertz pulses-remains a challenge. In this work, we introduce a simple method for generating circularly polarized terahertz radiation with an ellipticity of 0.99. By optimizing key parameters-BBO crystal tilt, rotation, position, and pump chirp-we achieve broadband circular polarization across 30 THz, with indications of further extent to 40 THz. This approach advances fundamental studies in terahertz optics and paves the way for adaptive sensing and next-generation terahertz communications. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Silicon dioxide is a suitable material to encapsulate proteins at room temperature so that they can be analyzed 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 optimization. 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.

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 is strongly reduced and reversed in samples with metallic behavior such as LaB6 and could not be found when multicycle 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 semimetallic 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 atom probe tomography and related applications.

Over the last decade, significant advances have been made in the implementation of high-performance benchtop pulsed THz sources featuring optical rectification of ultrashort light pulses in nonlinear crystals [1]. On the one hand, the use of lithium niobate (LN) crystals, with a tilted pulse front pumping (TPFP) configuration, has enabled the emergence of intense THz sources [2]. On the other hand, the development of diode-pumped ytterbium-doped lasers with high repetition rates has led to the advent of powerful THz sources [3]. These developments are timely because THz sources combining such performances, namely high intensity and high repetition rate, are essential for many applications such as matter analysis and manipulation [4].

The demand for precise, high-energy Extreme Ultraviolet (EUV) sources is growing across scientific and industrial fields. Studies have demonstrated that bulk crystals driven by mid-infrared laser pulses can generate high-order harmonics with enhanced intensities, extended cut-off energies, and improved damage thresholds [1]. While high-energy OPCPA and OPA systems have been successfully utilized to achieve these results, their complexity highlights the need for simpler, more compact solutions [1]–[3].

The thermal effect of a subpicosecond laser pulse impinging on a nanoscale semiconductor structure is evaluated by analyzing the photoluminescence (PL) from samples characterized in situ by atom probe tomography. By examining time-resolved PL and ion time-of-flight spectra, we establish the correct time scale of transient processes─carrier recombination and carrier-phonon scattering─following a laser pulse. This approach allows for analysis of peak energies and bandwidths from temperature- and laser intensity-dependent PL spectra, enabling the estimation of an effective temperature within a few hundred picoseconds after the laser pulse. The analysis was conducted on ZnO/(Mg,Zn)O quantum well heterostructures, where the results can be readily interpreted using ZnO's specific heat capacity and its temperature dependence.

We present findings on high harmonic generation (HHG) in solids utilizing a high-energy fiber laser system operating at 1550 nm. The driving laser source comprises an erbium-doped fiber chirped pulse amplifier (EDFA) combined with a post-compression stage employing a hollow-core photonic crystal fiber (HC-PCF) filled with noble gases. Nonlinear selfcompression in the HC-PCF enables the generation of ultrashort pulses with a duration of 50 fs and energy of 0.91 mu J at a repetition rate of 660 kHz. In a first step, harmonics up to H7 were observed when focusing the laser into small bandgap materials such as Zinc Oxide (ZnO). Subsequently, the system was enhanced to measure high harmonics in the extreme ultraviolet (XUV) range, with harmonics up to H25 observed using a large bandgap material, magnesium oxide (MgO). To the best of our knowledge, this represents the first solid-state HHG source driven by a high-energy few-cycle fiber laser in the telecom region.

Using a two-color plasma in air or gas allows for the generation of ultra-broadband and highly intense terahertz (THz) pulses. Precisely controlling the shape of THz pulses, particularly the carrier envelope phase, is crucial for a wide range of technological and scientific applications. Recent research has revealed that the phase difference between the fundamental laser wave and its second harmonic influences the shape of the emitted THz pulse. However, the combined impact of laser chirp and the air-dispersion-induced phase difference between the two colors has not been explored in detail. This study aims to fill this gap. The results show that both of these factors have a significant impact on the THz waveform and emitted pulse energy. Positive and negative chirps lead to distinct effects on the pulse shape. A positively chirped pump laser produces a THz waveform with a negative monopolar shape, while a negatively chirped pump laser results in a positive THz pulse shape. Additionally, our findings indicate that the relationship between THz pulse energy and chirp changes with variations in the specific phase difference between the first and second harmonics. These results underscore the importance of carefully tuning both parameters to achieve maximum generation efficiency for a given waveform.

The Photonic Atom Probe is applied to the study of nanoscale field-emission tip specimens containing a section of III-N device constituted by a sequence of alloyed and doped sections. Different sections produce specific but spectrally overlapping luminescence signals. The possibility of collecting photoluminescence spectra during the field evaporation of the specimen allows for disentangling different doping-related luminescence lines and to correlate the different spectral contributions to the specific properties of the doping distributions. In particular, the spectral components of the luminescence related to Mg impurities at energies between 3.0 eV and 3.3 eV have been investigated, and correlated with the Mg concentration and 3D distribution in different sections of the device.

The generation of terahertz radiation via laser-induced plasma from two-color femtosecond pulses in air has been extensively studied due to its broad emission spectrum and significant pulse energy. However, precise control over the temporal properties of these ultra-broadband terahertz pulses, as well as the measurement of their polarization state, remain challenging. In this study, we review our latest findings on these topics and present additional results not previously reported in our earlier works. First, we investigate the impact of chirping on the fundamental wave and the effect of manipulating the phase difference between the fundamental wave and the second-harmonic wave on the properties of generated terahertz pulses. We demonstrate that we can tune the time shape of terahertz pulses, causing them to reverse polarity or become bipolar by carefully selecting the correct combination of chirp and phase. Additionally, we introduce a novel technique for polarization characterization, termed terahertz unipolar polarimetry, which utilizes a weak probe beam and avoids the systematic errors associated with traditional methods. This technique is effective for detecting polarization-structured terahertz beams and the longitudinal component of focused terahertz beams. Our findings contribute to the improved control and characterization of terahertz radiation, enhancing its application in fields such as nonlinear optics, spectroscopy, and microscopy.

We present the application of THz monocycles to the Atom Probe Tomography (APT), an analytical microscope that allows the three-dimensional mapping of chemical heterogeneities in a material at the atomic scale. When a positive electric field of several volts per angstrom is applied to the surface of a material, the surface atoms evaporate as ions even at cryogenic temperatures, this is the work principle of APT. We prove that THz transient can induce the controlled evaporation of surface atoms due to the strong increase in the THz field in the near field of the sample. In addition, the use of THz pulses reduces the thermal effects reported when using laser pulses in the visible or near ultraviolet domain. We are also studying the effect of the THz pulses on the energy of the evaporated ions.

We investigate the microscopic behaviour of hydrogen-containing species formed on the surface of III-N semiconductor samples by the residual hydrogen in the analysis chamber in laser-assisted atom probe tomography (APT). We analysed AlGaN/GaN heterostructures containing alternate layers with a thickness of about 20 nm. The formation of H-containing species occurs at field strengths between 22 and 26 V/nm and is independent of the analysed samples. The 3D APT reconstruction makes it possible to map the evolution of the surface behaviour of these species issued by chemical reactions. The results highlight the strong dependence of the relative abundances of hydrides on the surface field during evaporation. The relative abundances of the hydrides decrease when the surface field increases due to the evolution of the tip shape or the different evaporation behaviour of the different layers.

The atomic-scale characteristics of stoichiometric lanthanum hexaboride (LaB6) material are investigated in this work using atom probe tomography (APT). The presence of a higher background level in the mass spectrum is attributed to continuous boron evaporation, causing preferential boron loss and affecting composition measurements. The measured composition in LaB6 exhibits inaccuracies influenced by the experimental conditions, particularly showing an excess of lanthanum (La). This enrichment is consistently linked to boron's tendency for continuous evaporation, leading to a higher fraction of multiple evaporation and detection events. Consequently, the susceptibility of boron to measurement errors is increased due to detector limitations. To address this issue, we propose a method of compositional correction based on pseudomultiple events and an abundance of isotopic pairs, which has been successfully applied to elements with two isotopes and has the potential for elements with multiple isotopes.

Terahertz (THz) radiation with low-energy photons (meV) is used in a wide range of applications, such as microscopy, sensing, and spectroscopy. However, recently, high amplitude THz pulses of MV/cm have been generated and used for electron emission and ion evaporation from field emitters, opening up the possibility of using high amplitude THz pulses for material imaging by THz-assisted atom probe tomography (APT). In this work, we compare the APT analyses of lanthanum hexaboride (LaB6) samples using a femtosecond near-infrared laser with those obtained using high-amplitude single-cycle THz pulses. The atomic-scale characterization of stoichiometric LaB6 is challenging in laser-assisted APT due to the detection losses of boron ions. Here, we show that the THz radiation reduces the emission of molecular ions and multiple detection events, and it increases the charge state of the emitted ions. All these effects result in an improvement in boron detection. Furthermore, the emission dynamics of boron and lanthanum ions differ in their evaporation times when using THz radiation. This work emphasizes the ability of high-amplitude, single-cycle THz pulses to well control material analysis in APT, leading to better results on chemical composition. It also paves the way for the use of this radiation for material manipulation.