arXiv subjects

Igor V. Litvinyuk

Publications and source records attributed to Igor V. Litvinyuk.

6 recordsLinked to original sources

arXiv2025

Ultrashort 30-fs laser photoablation for high-precision and damage-free diamond machining

A 30-fs, 800 nm, 1 kHz femtosecond was used to photoablate diamond across radiant energy doses of 1 - 500 kJ/cm^2, with fluences of 10 - 50 J/cm^2 and, pulse counts from 100 to 10,000. The objective was to maximise material removal while minimising surface roughness (Ra) by operating above the photoablation threshold. Results demonstrate that 30-fs laser photoablation achieves Ra <0.1 \mum, meeting both high- and ultra-high-precision machining standards, while maintaining surface integrity and preventing heat-affected zone (HAZ) damage. At 1 kJ/cm^2 (10 J/cm^2 fluence, 100 pulses), an Ra of 0.09 \mum was achieved, satisfying ultra-high precision criteria (Ra <0.1 \mum). Additionally, doses below 10 kJ/cm^2 consistently met high-precision machining requirements (Ra <0.2 \mum). Photoablation efficiency peaked below 50 kJ/cm^2, after which material removal diminished, indicating non-linear process limitations. The sp3-diamond phase remained intact, as confirmed by the unchanged T2g Raman mode at 1332 cm^-1, with no detectable Raman G or D modes, confirming the absence of sp2-related graphitization, structural disorder, of nitrogen vacancy (NV) centre annealing. These findings establish 30 fs laser processing as a high-precision, damage-free approach for diamond machining, with promising applications in NV centre-containing quantum materials and advanced tooling.

cond-mat.mtrl-sci↗

arXiv2022

Laser-Induced Graphitisation of Diamond Under 30 fs Laser Pulse Irradiation

The degree of laser-induced graphitisation from a sp3-bonded to a sp2-bonded carbon fraction in a single crystal chemical vapour deposited (CVD) diamond under a varying fluence of an ultrashort pulsed laser (30 fs, 800 nm, 1 kHz) irradiation has been studied. The tetrahedral CVD sp3-phase was found to transition to primarily an sp2-aromatic crystalline graphitic fraction below the critical fluence of 3.9 J/cm2, above which predominantly an amorphous carbon was formed. A fractional increase of fluence from 3.3 J/cm2 to 3.9 J/cm2 (~ 20 %) resulted in a substantial (~ three-fold) increased depth of the sp2-graphitised areas owing to the non-linear interactions associated with an fs-laser irradiation. Additionally, formation of C=O carbonyl group was observed below the critical threshold fluence; the C=O cleavage occurred gradually with the increase of irradiation fluence of 30 fs laser light. The implications for these findings on enhancement of fs-driven processing of diamond are discussed.

physics.chem-ph↗

arXiv2021

Attosecond delays of high harmonic emissions from isotopes of molecular hydrogen measured by Gouy phase XUV interferometer

High harmonic spectroscopy can access structural and dynamical information on molecular systems encoded in amplitude and phase of high harmonic generation (HHG) signals4. However, measurement of the harmonic phase is a daunting task. Here we present a precise measurement of HHG phase difference between two isotopes of molecular hydrogen using the advanced extreme-ultraviolet (XUV) Gouy phase interferometer. The measured phase difference is about 200 mrad, corresponding to 3 attoseconds (1 as = 10^-18 s) time delay which is nearly independent of harmonic order. The measurements agree very well with numerical calculations of a four-dimensional time-dependent Schroedinger equation. Numerical simulations also reveal the effects of molecular orientation and intra-molecular two-centre interference on the measured phase difference. This technique opens a new avenue for measuring the phase of harmonic emission for different atoms and molecules. Together with isomeric or isotopic comparisons it also enables the observation of subtle effects of molecular structures and nuclear motion on electron dynamics in strong laser fields.

physics.atom-ph↗

arXiv2021

Femtosecond laser micromachining of diamond: current research status, applications and challenges

Ultra-fast femtosecond (fs) lasers provide a unique technological opportunity to precisely and efficiently micromachine materials with minimal thermal damage owing to the reduced heat transfer into the bulk of the work material offered by short pulse duration, high laser intensity and focused optical energy delivered on a timescale shorter than the rate of thermal diffusion into the surrounding area of a beam foci. There is an increasing demand to further develop the fs machining technology to improve the machining quality, minimize the total machining time and increase the flexibility of machining complex patterns on diamond. This article offers an overview of recent research findings on the application of fs laser technology to micromachine diamond. The laser technology to precisely micromachine diamond is discussed and detailed, with a focus on the use of fs laser irradiation systems and their characteristics, laser interaction with various types of diamonds, processing and the subsequent post-processing of the irradiated samples and, appropriate sample characterisation methods. Finally, the current and emerging application areas are discussed, and the challenges and the future research prospects in the fs laser micromachining field are also identified.

cond-mat.mtrl-sci↗

arXiv2020

Observation of Dynamic Stark Resonances in Strong-Field Excitation

We investigate AC Stark-shifted resonances in argon with ultrashort near-infrared pulses. Using 30 fs pulses we observe periodic enhancements of the excitation yield in the intensity regions corresponding to the absorption of 13 and 14 photons. By reducing the pulse duration to 6 fs with only a few optical cycles, we also demonstrate that the enhancements are significantly reduced beyond what is measurable in the experiment. Comparing these to numerical predictions, which are in quantitative agreement with experimental results, we find that even though the quantum-state distribution can be broad, the enhancements are largely due to efficient population of a select few AC Stark-shifted resonant states rather than the closing of an ionization channel. Because these resonances are dependent on the frequency and intensity of the laser field, the broad bandwidth of the 6 fs pulses means that the resonance condition is fulfilled across a large range of intensities. This is further exaggerated by volume-averaging effects, resulting in excitation of the $5g$ state at almost all intensities and reducing the apparent magnitude of the enhancements. For 30 fs pulses, volume averaging also broadens the quantum state distribution but the enhancements are still large enough to survive. In this case, selectivity of excitation to a single state is reduced below 25% of the relative population. However, an analysis of TDSE simulations indicates that excitation of up to 60% into a single state is possible if volume averaging can be eliminated and the intensity can be precisely controlled.

physics.atom-ph↗

arXiv2013

Transition between mechanisms of laser-induced field-free molecular orientation

The transition between two distinct mechanisms for the laser-induced field-free orientation of CO molecules is observed via measurements of orientation revival times and subsequent comparison to theoretical calculations. In the first mechanism, which we find responsible for the orientation of CO up to peak intensities of 8 x 10^13 W/cm^2, the molecules are impulsively oriented through the hyperpolarizability interaction. At higher intensities, asymmetric depletion through orientation-selective ionization is the dominant orienting mechanism. In addition to the clear identification of the two regimes of orientation, we propose that careful measurements of the onset of the orientation depletion mechanism as a function of the laser intensity will provide a relatively simple route to calibrate absolute rates of non-perturbative strong-field molecular ionization.

physics.chem-ph↗