Aurélien Houard

Aurélien Houard
École Polytechnique · Laboratoire d'Optique Appliquée (LOA)

Ph.D.
Research scientist on femtosecond laser filamentation

About

170
Publications
29,139
Reads
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3,509
Citations
Introduction
My research activities focus on the nonlinear propagation of intense femtosecond laser pulses through transparent media and more specifically on the filamentation phenomena and its possible applications.
Additional affiliations
June 2009 - November 2020
École Polytechnique
Position
  • Leader of the Laser Matter Interaction group
Description
  • Research scientist
October 2005 - December 2008
ENSTA ParisTech, Ecole Polytechnique, CNRS
Position
  • Centre national de la recherche scientifique
Description
  • Ph.D. Thesis
Education
September 2004 - July 2005
Université Paris-Sud 11
Field of study
  • Plasma Physics
September 2002 - July 2005
Université Paris-Sud 11
Field of study
  • Fundamental Physics

Publications

Publications (170)
Preprint
Full-text available
Quantum interference occurs frequently in the interaction of laser radiation with materials, leading to a series of fascinating effects such as lasing without inversion, electromagnetically induced transparency, Fano resonance, etc. Such quantum interference effects are mostly enabled by single-photon resonance with transitions in the matter, regar...
Preprint
We report Second Harmonic Generation (SHG) and Third Harmonic Generation (THG) energy conversion efficiencies up to 59% and 27%, respectively for laser pulses simultaneously delivering high peak power in the sub-TW range and average powers in the sub-kW range. No damage or efficiency decrease is observed after more than 100 hours operation time. Th...
Article
Full-text available
Experiments and simulations are performed to study filamentation and generation of acoustic waves in water by loosely focused multi-millijoules laser pulses. When the laser pulse duration is increased from femtosecond to nanosecond duration, a transition is observed from a filamentary propagation with extended and low energy density deposition to a...
Article
Full-text available
We study the influence of the laser repetition rate on the generation of low-density channels of air left in the path of femtosecond laser filament. At high repetition rates, we observe the formation of a permanent millimeter-wide low-density channel that exceeds the depth and width of the transient depletion due to a single filament. We also show...
Article
We present a model describing ionization and excitation of nitrogen molecules by a strong and short laser pulse. Different from previous publications, both processes are considered within the same formalism of the density matrix. We account for the dependence of the dipole moment on the vibrational quantum number and for a large number of excited l...
Article
Full-text available
Postfilamentation channel resulting from filamentation of freely propagating 744-nm, 5-mJ, 110-fs pulse in the corridor air is examined experimentally and in simulations. The longitudinal extension of postfilament was determined to be 55–95 m from the compressor output. Using single-shot angle-wavelength spectra measurements, we observed a series o...
Article
We experimentally observed laser-induced remote high-voltage discharge triggering between two needle electrodes with half-a-cm spacing. The discharge was initiated by a 744-nm, 90-fs, 6-mJ laser pulse undergoing filamentation in air. For the direct voltage below the self-breakdown threshold, triggering of air-gap discharge was synchronized with a 1...
Article
Full-text available
Delayed cavity-free forward lasing at the wavelengths of 391 and 428 nm was observed in recent experiments in air or pure nitrogen pumped with an intense femtosecond laser pulse at wavelength of 800 nm. The mechanism responsible for the lasing is highly controversial. In this article we propose a model explaining the delayed lasing, which contains...
Article
Pulses at 744 nm with 90 fs duration, 6 mJ energy, and a weakly divergent wavefront propagate for more than 100 m and generate a filament followed by an unprecedently long high intensity (≥1TW/cm2) light channel. Over a 20 m long sub-section of this channel, the pulse energy is transferred continuously to the infrared wing, forming spectral humps t...
Article
The time profile of a lasing signal at 391.4 nm emitted by a weakly ionized gas of nitrogen molecules at low pressure is measured under double excitation with intense femtosecond laser pulses at 800 nm. An abrupt decrease in emission occurs at the time of arrival of the second pulse. It is explained by a transfer of population from ground to first...
Article
Full-text available
We report on the coherent control of boosted ultrashort terahertz pulses emitted from air plasma pumped by a femtosecond sawtooth pulse composed of three optical harmonic fields. With an inline optical setup, the relative phases between the three optical components of the pump pulse can be varied independently with attosecond precision without the...
Article
Full-text available
Lightning is highly destructive due to its high power density and unpredictable character. Directing lightning away would allow to protect sensitive sites from its direct and indirect impacts (electromagnetic perturbations). Up to now, lasers have been unable to guide lightning efficiently since they were not offering simultaneously terawatt peak p...
Article
Full-text available
Cavity-free lasing of N2+ induced by a femtosecond laser pulse at 800 nm is nearly totally suppressed by a delayed twin control pulse. We explain this surprising effect within the V-scheme of lasing without population inversion. A fast transfer of population between nitrogen ionic states X2Σg+ and A2Πu, induced by the second pulse, terminates the c...
Preprint
Full-text available
Cavity-free lasing of N$_2^+$ induced by a femtosecond laser pulse at 800~nm is nearly totally suppressed by a delayed twin pump pulse. We explain this surprising effect within the V-scheme of lasing without population inversion. A fast transfer of population between nitrogen ionic states X$^2\Sigma_g^+$ and A$^2\Pi_u$, induced by the second pulse,...
Preprint
Full-text available
Delayed cavity-free forward lasing at the wavelengths of 391 and 428 nm was observed in recent experiments in air or pure nitrogen pumped with an intense femtosecond laser pulse at wavelength of 800~nm. The mechanism responsible for the lasing is highly controversial. In this article we explain the delayed emission by the presence of long-lived pol...
Article
Full-text available
We report on the observation of backward lasing at 391.4 nm of nitrogen ions pumped by linearly polarized intense femtosecond pulses at 800 nm. The strongly enhanced spectral intensity at 391.4 nm, as well as the amplification of an externally injected backward seeding pulse, confirm that the backward 391.4 nm signal is due to optical amplification...
Article
Nitrogen molecules are promoted to excited neutral states during femtosecond laser pulse filamentary propagation in atmosphere, leading to a characteristic UV fluorescence. Using a laser-induced fluorescence depletion technique, we measure the formation dynamics of these excited neutral nitrogen molecules with femtosecond time resolution. We find t...
Article
Full-text available
We experimentally demonstrate the existence of long-lived coherent polarizations coupling simultaneously ground state X (X2Σg+) to excited states A (A2Πu) and B (B2Σu+) of N2+ inside a plasma created by a short intense laser pulse at 800 nm. This three-level V-scheme arrangement is responsible for a strong optical gain without population inversion...
Article
Full-text available
Third-harmonic (TH) generation inside air plasma filaments provides a simple method to convert near-infrared laser pulses in the UV range. Here, we report on the optimization of the third-harmonic generation during filamentation in the parameter space of focusing geometry, gas pressure, and incident laser pulse energy. It is observed that, in the n...
Conference Paper
Full-text available
Femtosecond lasers can form long plasma filaments over distances ranging from several centimetres to several meters which can be used advantageously for high speed flow control, in particular for drag reduction. Recently the first experimental demonstration of femtosecond energy deposition in a wind tunnel has been reported. This paper completes th...
Article
Full-text available
We study the use of frequency upconversion schemes of near-IR picosecond laser pulses and compare their ability to guide and trigger electric discharges through filamentation in air. Upconversion, such as Second Harmonic Generation, is favorable for triggering electric discharges for given amount of available laser energy, even taking into account...
Conference Paper
Full-text available
We attribute the mechanism of “lasing” action of nitrogen ions pumped by femtosecond IR pulses to a laser without inversion scheme. Numerical simulations reproduce well the temporal dynamics and pressure dependence of the emission.
Conference Paper
We review recent results on multi-wavelength multipulse schemes to control high-voltage discharges with ultrashort pulses, and discuss their implications on lightning control at atmospheric scale.
Article
Full-text available
When a flying object becomes supersonic, a concomitant increase in drag leads to a considerable rise in fuel consumption. We show experimentally that an embarked terawatt femtosecond laser can significantly decrease this drag. We measured a 50% transient reduction of drag on a test model placed in a supersonic wind tunnel at Mach 3. This effect was...
Article
We report on the optical transmission of near-infrared (1.8 μm) femtosecond laser pulses during multiple pulses laser ablation of fused silica surface. In addition to the previously reported ciliary white light phenomenon (Phys. Rev. Lett. 110, 097601 (2013)), two new optical transmission phenomena were observed for relatively low energy laser puls...
Conference Paper
Full-text available
The goal of this study is to demonstrate experimentally the “Laser Spike” concept in a supersonic flow. The “Laser Spike” uses a thin filament of plasma created by a femtosecond laser. This plasma filament formed by the TeraWatt laser pulse acts as a linear energy deposition upstream of the shock wave created by a blunt body. It has been found that...
Preprint
Full-text available
A cavity-free laser in the sky could lead to revolutionary improvements in optical remote sensing for atmospheric science. Abundant in air, nitrogen molecules are prime candidates as an active medium for such a laser. Nitrogen molecules, either neutral or singly ionized, exhibit a significant optical gain in the UV regime when pumped by an intense...
Chapter
Full-text available
In this chapter, we will discuss lasing actions in the air that follow the excitation with a short intense laser pulse at 800 nm. We will successively analyze two types of laser actions. The first type is based on the optical transition between the excited triplet states of the neutral nitrogen molecule. Based on the study of the dependence of the...
Conference Paper
Full-text available
Air pumped by mid-infrared femtosecond pulses gives rise to coherent emission at 391 nm. Based on ellipticity dependence measurement and time-resolved characterization, we attribute this emission to resonance-enhanced harmonics in perturbative regime.
Conference Paper
Air pumped by mid-infrared femtosecond pulses gives rise to coherent emission at 391/428 nm. Based on ellipticity dependence measurement and time-resolved characterization, we attribute this emission to resonance-enhanced low order harmonics.
Article
Full-text available
Nitrogen molecules in ambient air exposed to an intense near-infrared femtosecond laser pulse give rise to cavity-free superradiant emission at 391.4 and 427.8 nm. An unexpected pulse duration-dependent cyclic variation of the superradiance intensity is observed when the central wavelength of the femtosecond pump laser pulse is finely tuned between...
Article
Full-text available
A semiclassical model of electron rescattering in a strong laser field is applied to the evaluation of the probability of nitrogen molecular ion excitation. Depending on the ionization phase, a group of electrons oscillate around the parent ion for several laser periods and rescatter at large angles. The effect of ion attraction enhances significan...
Article
Full-text available
Laser filamentation offers a promising way for the remote handling of large electrical power in the form of guided arc discharges. We here report that it is possible to increase by several orders of magnitude the lifetime of straight plasma channels from filamentation-guided sparks in atmospheric air. A 30 ms lifetime can be reached using a low-int...
Article
Full-text available
We report on a theoretical study of cavity-free lasing of neutral nitrogen molecules in femtosecond laser filaments with a nonadiabatic Maxwell-Bloch model, compared with recent pump-seed experiments. The nonadiabaticity of the lasing process is revealed and it is found that electron-neutral collisions dominate the dipole dephasing rate. Moreover,...
Article
Full-text available
We demonstrate the coupling of microwave radiation into a plasma channel formed by laser filamentation in air, leading to the amplification by two orders of magnitude of longitudinal oscillations of the plasma. Transfer of this longitudinal excitation toward unexcited region of the plasma column occurs over >10 cm, in good agreement with a theoreti...
Article
Ce travail est relatif à l'étude expérimentale d'un problème d'opto-acoustique non linéaire, consistant à générer un signal acoustique dans l'eau à partir d'un laser pulsé térawatt (TW). La source acoustique obtenue a pu être reliée au phénomène de filamentation qui produit une contraction du faisceau initial, accompagnée de la formation d'un plasm...
Article
Full-text available
We investigate the dynamics of cavity-free lasing from neutral nitrogen molecules in femtosecond laser filaments. An important difference of intensity and temporal duration is observed between backward and forward lasing, in both amplified spontaneous emission and seed-amplification regimes. Numerical simulations based on a nonadiabatic Maxwell-Blo...
Article
Full-text available
We investigate experimentally the plasma dynamics of a centimeter-scale, laser filamentation-guided spark discharge. Using electrical and optical diagnostics to study monopolar discharges with varying current pulses we show that plasma decay is dominated by free electron recombination if the current decay time is shorter than the recombination char...
Article
Full-text available
The triggering and guiding of electric discharges produced in atmospheric air by a compact 100 kV Marx generator is realized in laboratory using an intense femtosecond laser pulse undergoing filamentation. We describe here an approach allowing extending the lifetime of the discharges by injecting a current with an additional circuit. Laser guiding...
Article
Full-text available
We study the propagation of intense, high repetition rate laser pulses of picosecond duration at 1.03 µm central wavelength through air. Evidence of filamentation is obtained from measurements of the beam profile as a function of distance, from photoemission imaging and from spatially resolved sonometric recordings. Good agreement is found with...
Article
Acoustic signals generated by filamentation of ultrashort TW laser pulses in water are characterized experimentally. Measurements reveal a strong influence of input pulse duration on the shape and intensity of the acoustic wave. Numerical simulations of the laser pulse nonlinear propagation and the subsequent water hydrodynamics and acoustic wave g...
Article
Full-text available
Laser filamentation is responsible for the deposition of a significant part of the laser pulse energy in the propagation medium. We found that using terawatt laser pulses and relatively tight focusing conditions in air, resulting in a bundle of co-propagating multifilaments, more than 60 % of the pulses energy is transferred to the medium, eventual...
Article
Full-text available
The propagation of near-infrared ultra-short laser pulses in the regime of anomalous dispersion of transparent solids is associated with a host of self-induced effects including a significant spectral broadening extending from the ultraviolet into the infrared region, pulse self-compression down to few-cycle pulse durations, free and driven third h...
Conference Paper
Acoustic signals generated by filamentation of TW laser pulses in water are characterized experimentally and numerically revealing a strong influence of the input pulse duration on the shape of the acoustic signal.
Conference Paper
We report on experimental evidence showing that the intense 391nm radiation emitted by air plasma is superradiance. Electron recollision is speculated to play an essential role in this superradiant process.
Chapter
Full-text available
Stimulated emissions in both backward and forward directions from a plasma filament in ambient air or pure nitrogen have been observed in recent years. In this article, we present our recent experimental results concerning the backward stimulated emission. We first demonstrate that backward stimulated emission from neutral N2 molecules can be effec...