Author
Q. Luo
Bio: Q. Luo is an academic researcher from Laval University. The author has contributed to research in topics: Laser & Femtosecond. The author has an hindex of 19, co-authored 29 publications receiving 1742 citations.
Papers
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TL;DR: In this paper, a femtosecond laser pulse propagates in an optical medium, self-focusing occurs, and the most powerful part of the pulse self focuses first during its propagation.
Abstract: When a powerful femtosecond laser pulse propagates in an optical medium, self-focusing occurs. Normally, it is the most powerful part (slice) of the pulse that self-focuses first during its propaga...
559 citations
06 Jun 2003
TL;DR: In this article, the backscattered fluorescence of nitrogen from long filaments generated by intense ultrafast Ti-sapphire laser pulses propagating in air is studied and it shows an exponential increase with increasing filament length, indicating amplified spontaneous emission (ASE).
Abstract: The backscattered fluorescence of nitrogen from long filaments generated by intense ultrafast Ti-sapphire laser pulses propagating in air is studied It shows an exponential increase with increasing filament length, indicating amplified spontaneous emission (ASE)
230 citations
TL;DR: In this article, the authors observed a universal phenomenon of the competition among multiple filaments generated during the propagation of intense femtosecond laser pulses in air, and they showed that the fluorescence signal from the excitation of nitrogen molecules inside the plasma channel contains important information pertaining to the formation and interaction of multiple filament.
Abstract: We observed a universal phenomenon of the competition among multiple filaments generated during the propagation of intense femtosecond laser pulses in air. We show that the fluorescence signal from the excitation of nitrogen molecules inside the plasma channel contains important information pertaining to the formation and interaction of multiple filaments. The detected backscattered nitrogen fluorescence from inside the filaments yielded irregular changes from shot to shot which cannot be explained by fluctuation arising from the initial laser pulse itself. Numerical simulations reveal a complex dynamics of multiple filament propagation and interaction dynamics that depends strongly on the initial perturbations of the laser beam. The irregular changes of the fluorescence signal are attributed to the interference between adjacent hot spots that evolve into filaments which give rise to new hot spots (filaments) in between, and thus give the appearance of the fusion or branching of filaments.
128 citations
TL;DR: In this article, the authors present an overview of the recent progress in their laboratory concerning the remote sensing of chemical and biological agents/pollutants in air using filamentation-induced nonlinear fluorescence techniques.
Abstract: All matters in the path of filaments induced by an intense femtosecond laser pulse propagating in air could be fragmented and result in the emission of characteristic fluorescence spectra from the excited fragments. The fluorescence spectra exhibit specific signatures (fingerprints) that can be used for the identification of various substances including chemical and biological species. In this paper, we present an overview of the recent progress in our laboratory concerning the “remote” sensing of chemical and biological agents/pollutants in air using filamentation-induced nonlinear fluorescence techniques.
126 citations
TL;DR: In this article, the fluorescence spectrum of ethanol molecules induced by femtosecond laser pulses has been recorded as the fingerprint of the molecules, and it was demonstrated that if this is combined with a LIDAR-based technique, fluorescence from pollutants in the atmosphere could be detected over a long distance.
Abstract: The fluorescence spectrum of ethanol molecules induced by femtosecond laser pulses has been recorded as the fingerprint of the molecules. It was demonstrated that, if this is combined with a LIDAR technique, the fluorescence from pollutants in the atmosphere could be detected over a long distance.
98 citations
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TL;DR: In this paper, the main aspects of ultrashort laser pulse filamentation in various transparent media such as air (gases), transparent solids and liquids are introduced and discussed.
2,282 citations
TL;DR: In this article, the authors present the landmarks of the 10-odd-year progress in this field, focusing on the theoretical modeling of the propagation equations, whose physical ingredients are discussed from numerical simulations.
Abstract: Modern laser sources nowadays deliver ultrashort light pulses reaching few cycles in duration and peak powers exceeding several terawatt (TW). When such pulses propagate through optically transparent media, they first self-focus in space and grow in intensity, until they generate a tenuous plasma by photo-ionization. For free electron densities and beam intensities below their breakdown limits, these pulses evolve as self-guided objects, resulting from successive equilibria between the Kerr focusing process, the chromatic dispersion of the medium and the defocusing action of the electron plasma. Discovered one decade ago, this self-channeling mechanism reveals a new physics, widely extending the frontiers of nonlinear optics. Implications include long-distance propagation of TW beams in the atmosphere, supercontinuum emission, pulse shortening as well as high-order harmonic generation. This review presents the landmarks of the 10-odd-year progress in this field. Particular emphasis is laid on the theoretical modeling of the propagation equations, whose physical ingredients are discussed from numerical simulations. The dynamics of single filaments created over laboratory scales in various materials such as noble gases, liquids and dielectrics reveal new perspectives in pulse shortening techniques. Far-field spectra provide promising diagnostics. Attention is also paid to the multifilamentation instability of broad beams, breaking up the energy distribution into small-scale cells along the optical path. The robustness of the resulting filaments in adverse weathers, their large conical emission exploited for multipollutant remote sensing, nonlinear spectroscopy and the possibility of guiding electric discharges in air are finally addressed on the basis of experimental results.
858 citations
TL;DR: The experimental observation of curved plasma channels generated in air using femtosecond Airy beams, where the tightly confined main intensity feature of the axially nonsymmetric laser beam propagates along a bent trajectory, leaving a curved plasma channel behind.
Abstract: Plasma channel generation (or filamentation) using ultraintense laser pulses in dielectric media has a wide spectrum of applications, ranging from remote sensing to terahertz generation to lightning control. So far, laser filamentation has been triggered with the use of ultrafast pulses with axially symmetric spatial beam profiles, thereby generating straight filaments. We report the experimental observation of curved plasma channels generated in air using femtosecond Airy beams. In this unusual propagation regime, the tightly confined main intensity feature of the axially nonsymmetric laser beam propagates along a bent trajectory, leaving a curved plasma channel behind. Secondary channels bifurcate from the primary bent channel at several locations along the beam path. The broadband radiation emanating from different longitudinal sections of the curved filament propagates along angularly resolved trajectories.
746 citations
TL;DR: In this paper, a femtosecond laser pulse propagates in an optical medium, self-focusing occurs, and the most powerful part of the pulse self focuses first during its propagation.
Abstract: When a powerful femtosecond laser pulse propagates in an optical medium, self-focusing occurs. Normally, it is the most powerful part (slice) of the pulse that self-focuses first during its propaga...
559 citations
TL;DR: By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time.
Abstract: We report the experimental results and theoretical analysis of broadband detection of terahertz (THz) waves via electric-field-induced second-harmonic generation in laser-induced air plasma with ultrashort laser pulses. By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time. Our results show that, depending on the probe intensity, detection of THz waves in air can be categorized as incoherent, hybrid, and coherent detection. Coherent detection is achieved only when the tunnel ionization process dominates in gases.
415 citations