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We demonstrate for the first time the possibility to generate long plasma channels up to a distance of 1 km, using the terawatt femtosecond T&T laser facility. The plasma density was optimized by adjusting the chirp, the focusing and beam diameter. The interaction of filaments with transparent and opaque targets was studied.
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... [11][12][13][14][15][16] Laser filaments are selfsustained of around a dozen micrometers in diameter and up to hundreds of meters in length, greatly extending the traditional linear diffraction limit. [17][18][19][20][21] Properties of filaments such as their stability under air turbulence and their interaction with water droplets have been studied. [22][23][24] The creation of the filament is accompanied by an expanding shock wave that displaces water droplets in its immediate vicinity to create a cylindrical channel within which the signal beam can travel unobstructed. ...
... Previously, transmission of LG beams over long distances in the atmosphere have been demonstrated. 44 Recently, multifilaments have been demonstrated 45 over a short distance using structured light beams and over hundreds of meters 17,46 with Gaussian beams. In our experiment, the channel diameter estimated using the signal carrier is .1-mm. ...
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Dynamic media such as atmospheric clouds and fog form a formidable barrier to light propagation for free-space optical communication (FSO). To overcome such an obstacle, we propose to make use of the acoustic properties of a laser filament coupled together with a donut-shaped signal beam. A filament generated by an ultrafast laser is accompanied by an acoustic wave that clears a cylindrical chamber around the filament’s plasma column that can mimic a transmission channel. We present a method to couple a Laguerre–Gauss beam through the obstacle-free channel. We image and measure the transmitted signal carried by the structured beam to demonstrate an efficient method for FSO through cloudy conditions, which requires low energy, is resilient to noise, and is unaffected by the filament.
... The resulting dynamical balance gives rise to self-guided light structures known as filaments. Filaments can extend over atmospheric scale distances [6,7], opening the way to various applications from remote sensing [8] to lightning control [9][10][11][12][13][14], THz generation [15][16][17][18][19][20], fog clearing [21,22], or the triggering of condensation in sub-saturated atmospheres [8,23,24]. Filaments show very characteristic and even spectacular features, including long-distance propagation, bright light emission due to both plasma emission on the side and spectral broadening in the forward direction, and noise associated to the shockwave [25][26][27]. ...
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We experimentally investigate fluctuations in the spectrum of ultrashort laser pulses propagating in air, close to the critical power for filamentation. Increasing the laser peak power broadens the spectrum while the beam approaches the filamentation regime. We identify two regimes for this transition: In the center of the spectrum, the output spectral intensity increases continuously. In contrast, on the edges of the spectrum the transition implies a bimodal probability distribution function for intermediate incident pulse energies, where a high-intensity mode appears and grows at the expense of the original low-intensity mode. We argue that this dual behavior prevents the definition of a univoquial threshold for filamentation, shedding a new light on the long-standing lack of explicit definition of the boundary of the filamentation regime.
... Solution of these problems is directly related to transportation of high radiation power density to a target point in space. Here, the use of filaments have been put on a logically sound basis, i.e. they are characterized by the highest intensity, small size (several hundred microns) and angular divergence (up to several tens of μrad), large extent (hundreds of meters), and high resistance to external effects such as turbulence, presence of aerosols, etc. [1,9,10]. It is necessary to learn how to control these light channels over long distances to use filaments in solving problems of atmospheric optics. ...
... At intensities on the order of 10 13 W/cm 3 or higher, secondary radiation can be generated which disrupts the operation of electronics and thus shows to be a possible application for sensor damage and electronic countermeasures [21]. When partnered with work showing that filamentation can extend kilometers in distance [22,23] and transmit through clouds [24] and fog [25], the potential uses for these systems as successful directed-energy instruments really shines [26]. Building on these advancements, opportunities for using femtosecond pulses and induced filamentation for secure free-space communication networks opened up. ...
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Chirped pulse amplification (CPA) followed by nonlinear optical (NLO) systems constitute the backbone of myriad advancements in semiconductor and additive manufacturing, communication networks, biology and medicine, defense and national security, and a host of other sectors over the past decades. However, accurately and efficiently modeling CPA- and NLO-based laser systems is challenging because of the multitude of coupled linear and nonlinear processes and high variability in modeling frameworks. The lack of fully-integrated software CPA+NLO modeling severely hampers further advances to tailor existing or materialize new CPA+NLO systems and curtails their full potential in emerging inverse design approaches through data-driven machine learning methods. Here, we present a modular start-to-end software model, allowing for the inclusion of an array of amplifier designs and nonlinear optics techniques, which renders time- and frequency-resolved electromagnetic fields alongside essential physical characteristics on energy, fluence, and spectral distribution. To demonstrate its robustness and real-world applicability -- specifically, reverse engineering, system optimization, and inverse design -- we present a case study on the LCLS-II photo-injector laser, representative of a high-power and spectro-temporally complex CPA+NLO system.
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Lightning discharges between charged clouds and the Earth’s surface are responsible for considerable damages and casualties. It is therefore important to develop better protection methods in addition to the traditional Franklin rod. Here we present the first demonstration that laser-induced filaments—formed in the sky by short and intense laser pulses—can guide lightning discharges over considerable distances. We believe that this experimental breakthrough will lead to progress in lightning protection and lightning physics. An experimental campaign was conducted on the Säntis mountain in north-eastern Switzerland during the summer of 2021 with a high-repetition-rate terawatt laser. The guiding of an upward negative lightning leader over a distance of 50 m was recorded by two separate high-speed cameras. The guiding of negative lightning leaders by laser filaments was corroborated in three other instances by very-high-frequency interferometric measurements, and the number of X-ray bursts detected during guided lightning events greatly increased. Although this research field has been very active for more than 20 years, this is the first field-result that experimentally demonstrates lightning guided by lasers. This work paves the way for new atmospheric applications of ultrashort lasers and represents an important step forward in the development of a laser based lightning protection for airports, launchpads or large infrastructures. A terawatt laser filament is shown to be able to guide lightning over a distance of 50 m in field trials on the Säntis mountain in the Swiss Alps.
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Filamentation is favorable for many long-range outdoor laser applications, some of which require propagation to or at high altitudes. Understanding how the filamentation process and filament properties are impacted by the low pressure conditions present at high altitudes is essential in designing effective applications. The scaling of filament preconditions with pressure is considered. An increase in critical power and decrease in transition numerical aperture (NA) is predicted to occur with a drop in pressure, indicating that nonlinear pulse propagation and filamentation at high altitudes requires higher energy and a longer assisted focal length than sea level filamentation. A summary of pressure-scaled filament properties is also presented. New simulations demonstrate filamentation at pressures as low as 0.0035 atm (38.5 km altitude) is possible.
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We report an investigation of white-light continuum generation and self-focusing by 140-fs Ti:sapphire laser pulses in extended transparent media. It is found that continuum generation is triggered by self-focusing and that both phenomena depend on the medium’s bandgap. There is a bandgap threshold for continuum gen- eration. Above that threshold the continuum’s width increases with increasing bandgap. Furthermore, the beam’s self-focal diameter is discontinuous across the threshold. To explain the observations a mechanism is proposed that involves multiphoton excitation of electrons into the conduction band at the self-focus; the gen- erated free electrons cause spectral superbroadening and limit the self-focal diameter. The continuum beam’s surprisingly low divergence is then investigated and explained in terms of a Kerr lensing effect.
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The propagation of a multi-terawatt femtosecond laser pulse in air is studied as a function of initial chirp. The chirp conditions for optimising air ionisation at long distance are presented. Ionisation channels are observed over a distance reaching 400 m.
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We observed the universal phenomenon of competition among multiple filaments generated during the propagation of intense femtosecond laser pulses in air. The backscattered fluorescence signal of nitrogen molecules excited inside multiple filaments yielded irregular changes from shot to shot without any correlation to the laser energy fluctuations. Numerical simulations reveal that the irregular fluorescence signal is due to a complex dynamics of interacting multi‐filaments. In particular, we show that interference effects between two hot spots, that give rise two filaments, may either fuse together or further branch out creating new filaments. This process is determined by the separation of hot spots in the beam and thus is very sensitive to the initial laser pulse input conditions. Steep
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The influence of air turbulence on femtosecond laser filamentation is studied experimentally and numerically for laser powers of a few critical powers. Air turbulence in the path of the beam prior to filamentation induces a large pointing and formation instability attributed to an increase of the self-focusing distance and higher modulational instability in the presence of turbulence. By contrast, previously formed filaments are robust both in terms of beam pointing accuracy and survival when crossing turbulent air.
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We show that laser filamentation can be initiated and propagate through strong extended turbulence well above the typical atmospheric values. We suggest that the effect of turbulence on filamentation is characterized by the product of the structure parameter for the refractive index C-n(2) and the length L of the turbulence region. Half of the filaments are transmitted for (CnL)-L-2 <= 4.4 x 10(-10) m(1/3). Moreover, the surviving filaments keep their key spectral properties including correlations inside the white-light continuum. (C) 2007 American Institute of Physics.
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This paper introduces and discusses the main aspects of ultrashort laser pulse filamentation in various transparent media such as air (gases), transparent solids and liquids. The properties of femtosecond filaments and their applications are presented. Theoretical models developed to explain filaments and the main predictions inferred from these models are reviewed. The various techniques to observe filaments and to measure their characteristics are described. The main measurements of filament features performed so far are reviewed.
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In a 2.8 m positive rod–plane air gap, we have studied how a plasma channel produced by focusing a 200 mJ ultrashort laser beam is able to trigger and guide a leader discharge. We have observed that the plasma channel allowed the lowering of the leader inception voltage by 50% and the guiding of the leader propagation on a distance of up to 2.3 m, with a tenfold increase of its speed. This led to an effective 40% reduction of the breakdown voltage. For the conditions studied here, the laser energy per unit length required to guide a leader is between 60 and 100 mJ/m. © 2000 American Institute of Physics.
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Using femtosecond filaments for the ablation of GaAs in air, we have observed that the diameter and volume of the resulting ablation craters remained almost constant with propagation distance. This constant mass removal along the propagation of a filament in both focused and non-focused configurations is valuable for applications such as material processing and stand-off laser-ablation based spectroscopy.