arXiv subjects

Yves Bellouard

Publications and source records attributed to Yves Bellouard.

15 recordsLinked to original sources

arXiv2023

Femtosecond laser direct-write photoconductive patterns on tellurite glass

We report the formation of arbitrary photoconductive patterns made of tellurium (Te) nanocrystals by exposing a tellurite (TeO2-based) glass to femtosecond laser pulses. During this process, Te/TeO2-glass nanocomposite interfaces with photoconductive properties form on the tellurite glass substrate. We show that these laser-written patterns have a highly reproducible photo-response, from the near ultraviolet (263 nm) to the visible spectrum, stable over a few months. Specifically, high responsivity (16.55 A/W) and detectivity (5.25*10^11 Jones) of a single laser-written line pattern are measured for an illumination dose of 0.07 mW/cm^2 at 400 nm. This work illustrates a pathway for locally turning a tellurite glass into functional photoconductor of arbitrary shape, without adding materials and using a single laser process step.

physics.optics↗

arXiv2022

Femtosecond laser-shockwave induced densification in fused silica

Tightly focused femtosecond laser-beam in the non-ablative regime can induce a shock-wave enough to reach locally pressures in the giga-Pascal range or more. In a single beam configuration, the location of the highest-pressure zone is nested within the laser-focus zone, making it difficult to differentiate the effect of the shock-wave pressure from photo-induced and plasma relaxation effect. To circumvent this difficulty, we consider two spatially separated focused beams that individually act as quasi-simultaneous pressure-wave emitters. The zone where both shock-waves interfere constructively forms a region of extreme pressure range, physically separated from the regions under direct laser exposure. Here, we present evidences of pressured-induced densification in fused silica in between the foci of the two beams, which can be exclusively attributed to the superposition of the pressure waves emitted by each focused laser-beam. Specifically, we show how the beams gap and pulses time-delay affect the structural properties of fused silica using Raman characterization, beam deflection technique, and selective etching techniques. The method is generic and can be implemented in a variety of transparent substrates for high-pressure physics studies and, unlike classical methods, such as the use of diamond anvils, offers a means to create arbitrary-shaped laser-induced high-pressure impacted zones by scanning the two beams across the specimen volume

physics.optics↗

arXiv2022

On the abnormal temperature dependent elastic properties of fused silica irradiated by ultrafast lasers

Materials with thermal-invariant elastic properties of materials are of interest for resonant device frequency and dimensional stability of precision devices. Here, we demonstrate that the temperature coefficient of elasticity (TCE) of amorphous silica can be locally reduced using femtosecond laser irradiation. Notably, a self-organized laser-induced modification shows a decrease of the TCE beyond 50%. The origin of this dramatic decrease is attributed to the presence of sub-micron permanent densified zones within the fine multi-layers structure of the laser-modified zone.

cond-mat.mtrl-sci↗

arXiv2022

On the uniaxial static stress relaxation in fused silica at room temperature

The question of whether static stress in fused silica relaxes at room temperature is still under debate. Here, we report experimental data investigating stress relaxation dynamics in fused silica at room temperature and up to 2 GPa stress levels under static loading conditions. Our measurements are performed using an innovative combination of methods; a femtosecond laser is used to accurately load a monolithic microscale test beam in a non-contact manner, fabricated using femtosecond laser processing and chemical etching, while the stress is continuously monitored using photoelasticity over an extended period spanning several months, in both dry and normal atmospheric conditions. The results are of practical importance, not only for photonics devices making use of stress-induced birefringence but also for flexures subjected to static loads.

physics.app-ph↗

arXiv2021

Few pulses femtosecond laser exposure for high efficiency 3D glass micromachining

Advanced three-dimensional manufacturing techniques are triggering new paradigms in the way we design and produce sophisticated parts on demand. Yet, to fully unravel its potential, a few limitations have to be overcome, one of them being the realization of high-aspect-ratio structures of arbitrary shapes at sufficiently high resolution and scalability. Among the most promising advanced manufacturing methods that emerged recently is the use of optical non-linear absorption effects, and in particular, its implementation in 3D printing of glass based on femtosecond laser exposure combined with chemical etching. Here, we optimize both laser and chemical processes to achieve unprecedented aspect ratio levels. We further show how the formation of pre-cursor laser-induced defects in the glass matrix plays a key role in etching selectivity. In particular, we demonstrate that there is an optimal energy dose, an order of magnitude smaller than the currently used ones, yielding to higher process efficiency and lower processing time. This research, in addition to a conspicuous technological advancement, unravels key mechanisms in laser-matter interactions essential in chemically-based glass manufacturing and offers an environmentally-friendly pathway through the use of less-dangerous etchants, replacing the commonly used hydrofluoric acid.

physics.app-ph↗

arXiv2021

Direct-write laser-induced self-organization and metallization beyond the focal volume in tellurite glass

We report on a self-organized process initiated on a potassium-tungsten-tellurite glass surface under repetitive femtosecond laser irradiation in a regime where cumulative effects lead to a localized melting. Specifically, we show that self-organized periodic patterns consisting of parallel nanoplanes perpendicular to the laser polarization are forming and extending beyond the zone under direct laser exposure. Examination of the modified regions revealed a phase change from a glassy tellurium-oxide to a crystalline elemental tellurium. In addition, we observe that this self-organization process, associated with elemental redistribution and deoxygenation, is triggered by the optical-field strength. We suggest that early self-organized nanostructures formed by a local-field enhancement is subsequently reinforced by a metallization event in an open-air atmosphere.

cond-mat.mtrl-sci↗

arXiv2020

Wavelength-multiplexed single-shot ptychography

Diagnostics capable of interrogating dynamics in harsh environments such as plasma have remained essentially unchanged in recent decades. Developments in advanced microscopy techniques will improve our understanding of the physics involved in these events. Recently developed single-shot ptychography (SSP) provides a pathway towards sophisticated plasma metrologies. Here we introduce wavelength-multiplexed single-shot ptychography (WM-SSP), which allows for hyperspectral, spatially and temporally resolved phase and amplitude contrast imaging. Furthermore, we introduce a novel probe constraint common to all wavelength multiplexed modalities in the single-shot geometry and present modifications to SSP that improve reconstruction fidelity and robustness. WM-SSP was experimentally realized and simulations show the technique's ability to deconvolve the electron and neutral densities within the plasma. WM-SSP will pave the way to a new generation of quantitative plasma imaging techniques.

physics.optics↗

arXiv2019

Optomechanical suspended waveguide for broadband phase modulation with frequency memory effect

Whether it is for transmitting information or for controlling intensity, light modulation is among the essential functions commonly used in complex optical systems. In integrated optics, modulation principles usually include the use of electro-optical effects or acousto-optics varying index waves. Here, we demonstrate a concept of light-modulation based on a vibrating suspended cantilever clamped on both ends, acting as an optical waveguide. In this approach, an optical phase shift is introduced by the physical elongation and by the stress induced in the vibrating cantilever. Most interesting, such a device can store optical information in the form of a phase shift, related to the frequency path-dependence of the vibration. This remarkable property stems from the intrinsic non-linear dynamical behavior of the device, resembling Duffing-like oscillators. In this proof-of-concept, the micro-device is manufactured in a single fused silica chip using femtosecond laser exposure combined with chemical etching and CO2-laser polishing to achieve optical roughness quality. The cantilever vibration results from dielectrophoresis forces arising in the silica beam as a consequence of the non-uniform electrostatic field applied to it. Noticeably, being made entirely of fused silica, the device is capable of broadband operation, from the near UV to the mid-IR range, and this, at kHz frequencies.

physics.optics↗

arXiv2018

Silicon formation in bulk silica through femtosecond laser engraving

Non-linear absorption phenomena induced by controlled irradiation with a femtosecond laser beam can be used to tailor materials properties within the bulk of substrates. One of the most successful applications of this technique is the ability to fabricate three-dimensional micro-devices integrating optical, mechanical or fluid handling functions in a single substrate. In this context, amorphous SiO2 is the most widely studied material. Here we show that short (50-fs) femtosecond pulses induce the separation of Si and O ions in SiO2 substrates, leading to the formation of micro-crystallites that we identify as pure crystalline phase of Si. Interestingly, this polymorphic phase transformation occurs in the absence of laser-induced confined microexplosion and with moderate numerical aperture. These findings not only unravel a key mechanism related to the transformation of the material and its subsequent properties, but also pave the road for the development of three-dimensional Si-rich structures embedded in a pure silica phase, eventually leading to novel disruptive approaches for fabricating three- dimensional micro-devices. For instance, one could imagine a silica-host substrate, in which arbitrary three-dimensional silicon-based components are direct-write using a femtosecond laser, rather than through assembly of components coming out of different substrates or using multiple processing steps.

cond-mat.mtrl-sci↗

arXiv2017

Unravelling brittle fracture statistics out of self-healing patterns forming during femtosecond laser exposure

Femtosecond laser written patterns at the surface of brittle materials may show a regenerative random transition from self-organized to disordered structures. Here, we show that this random intermittent behaviour carries relevant fracture statistics information, such as the so-called Weibull parameters. Furthermore, we draw a phenomenological analogy with idle and busy periods arising in queueing systems that we used to establish that these successive laser generated cycles are statistically independent. Based on this analogy and together with microscopic observations, we propose an experimental method bypassing the need for many specimens to build-up statistically relevant ensembles of fracture tests. This method is potentially generic as it may apply to a broad number of brittle materials.

cond-mat.mtrl-sci↗

arXiv2016

Femtosecond laser direct-write waveplates based on stress-induced birefringence

The use of femtosecond lasers to introduce controlled stress states has recently been demonstrated in silica glass. We use this technique, in combination with chemical etching, to generate and control stress-induced birefringence over a well-defined region of interest, demonstrating direct-write wave plates with precisely tailored retardance levels. This tailoring enables the fabrication of laser-written polarization optics that can be tuned to any wavelength for which silica is transparent and with a clear aperture free of any laser modifications. Using this approach, we achieve sufficient retardance to act as a quarter-wave plate. The stress distribution within the clear aperture is analyzed and modeled, providing a generic template that can be used as a set of design rules for laser-machined polarization devices.

physics.optics↗

arXiv2015

Formation of in-volume nanogratings with sub-100 nm periods in glass by femtosecond laser irradiation

We present direct experimental observation of the morphological evolution during the formation of nanogratings with sub-100-nm periods with the increasing number of pulses. Theoretical simulation shows that the constructive interference of the scattering light from original nanoplanes will create an intensity maximum located between the two adjacent nanoplanes, resulting in shortening of the nanograting period by half. The proposed mechanism enables explaining the formation of nanogratings with periods beyond that predicted by the nanoplasmonic model.

physics.optics↗

arXiv2014

Plasma waves excited at interface by femtosecond laser irradiation enabling formation of volume nanograting in glass

Irradiation of intense ultrafast laser pulses in glasses can lead to formation of nanogratings whose periods are significantly smaller than the incident irradiation wavelength. The mechanism of the exotic phenomenon is still under debate. Here, we access the snapshots of morphologies in the laser affected regions in a porous glass which reveal the evolution of the formation of nanogratings with increasing number of laser pulses. Combined with further theoretical analyses, our observation provides important clues which suggest that excitation of standing plasma waves at the interfaces between areas modified and unmodified by the femtosecond laser irradiation plays a crucial role for promoting the growth of periodic nanogratings. The finding indicates that the formation of volume nanogratings induced by irradiation of femtosecond laser pulses is initiated with a mechanism similar to the formation of surface nanoripples.

physics.optics↗

arXiv2014

On the anisotropy of stress-distribution induced in glasses and crystals by non-ablative femtosecond laser exposure

Femtosecond laser exposure in the non-ablative regime induces a variety of bulk structural modifications, in which anisotropy may depend on the polarization of the writing beam. In this work, we investigate the correlation between polarization state and stress anisotropy. In particular, we introduce a methodology that allows for rapid analysis and visualization of laser-induced stress anisotropy in glasses and crystals. Using radial and azimuthal polarization, we also demonstrate stress states that are nearly isotropic.

physics.optics↗

arXiv2014

Kinetics of Laser-Assisted Carbon Nanotube Growth

Laser-assisted chemical vapour deposition (CVD) growth is an attractive mask-less process for growing locally aligned carbon nanotubes (CNTs) in selected places on temperature sensitive substrates. The nature of the localized process results in fast carbon nanotube growth with high experimental throughput. Here, we report on detailed investigation of growth kinetics related to physical and chemical process characteristics. Specifically, the growth kinetics is investigated by monitoring the dynamical changes of reflected laser beam intensity during growth. Benefiting from the fast growth and high experimental throughput, we investigate a wide range of experimental conditions and propose several growth regimes. Rate-limiting steps are determined using rate equations linked to the proposed growth regimes, which are further characterized by Raman spectroscopy and Scanning Electron Microscopy (SEM), therefore directly linking growth regimes to the structural quality of the CNTs. Activation energies for the different regimes are found in the range of 0.3 - 0.8 eV.

physics.chem-ph↗