Long-wave Infrared Megafilaments in Air

Tochitsky, Sergei; Welch, Eric; Polyanskiy, Mikhail; Pogorelsky, Igor; Παναγιωτόπουλος, Πάρις; Kolesík, M.; Wright, E. M.; Koch, S. W.; Moloney, Jerome V.; Joshi, C.

doi:10.1364/nlo.2019.nw2a.1

Cited by 5 publications

(14 citation statements)

References 3 publications

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“…Laser excitation of single 3D spherical water droplets of different sizes irradiated by near-to far-IR pulses of 150 fs duration (full width at half maximum) is studied, showing the averaged intensity and electron density distributions in the propagation plane x0z, as shown in Figure 1. We focus on particular laser wavelengths of 800 nm, 1.5 μm, 3.9 μm, and 10 μm, which have found applications in filamentation and self-trapped beam propagation, [22,23] fog clearing, [10][11][12] laser ablation, [17,18] and so on. Plane wave excitation is considered, imitating the cases where the laser beam waist is much larger than the typical dimensions of aerosols or water droplets.…”

Section: Resultsmentioning

confidence: 99%

Tunable Near‐ to Far‐Infrared Optical Breakdown in Nonlinear Interactions of Ultrashort Laser Pulses with Water Microdroplets in Ambient Air

Rudenko

Moloney

2020

Advanced Photonics Research

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Water droplets are omnipresent in biophysical environments and ecosystems, playing an important role in communication through the atmosphere (i.e., aerosols and contaminants, fog, mist, haze, drizzle, clouds) and being involved in a variety of physicochemical reactions and biological processes (respiratory droplets due to breathing, talking, coughing, etc., biological cells, bioaerosols, water clusters, surface adhesion, and wettability). Broad opportunities in analysis, detection, and control over droplet distributions are enabled by the application of powerful lasers used for laser breakdown, [1-3] electron photoemission [4-7] and cavity-enhanced droplet spectroscopy, [8,9] long-distance optical communications, [10-12] and high harmonic generation from water microdroplets. [13-15] The processes of ultrashort laser excitation and ionization of water droplets and aerosols remain poorly explored for a wide range of photon energies and wavelengths from visible to long-wave infrared (IR) range. Within this spectral range, the contributions of scattering and absorption in water, [16] photo-and avalanche ionization, [17,18] positive and negative transient refractive index modifications due to free carrier heating, [19,20] as well as diffraction, Kerr self-focusing, and plasma defocusing upon propagation in the atmosphere [21-23] play interchangeable roles, making indispensable a comprehensible broad-frequency study of laser-induced nonlinear processes and optical breakdowns in laser-droplet interactions. Our current study addresses aspects of high-intensity femtosecond laser interaction with a single water microdroplet in ambient air for a wide range of laser wavelengths. Depending on the droplet size and wavelength (in Rayleigh, Mie, or geometrical optics [GO] ranges [24]), different complex field patterns are induced inside the droplet, contributing to extreme energy confinement due to a nanofocusing effect. [25] Such strong intensities result in electron plasma generation inside the droplets due to photo-and avalanche ionization processes, [11,26-30] changing locally the transient optical properties of water, influencing pulse propagation, and contributing to strong absorption. The effect of nanoscale electron plasma confinement inside microdroplets is comparable to ultrashort laser-induced plasma formation in the vicinity of plasmonic nanoparticles, routinely used for cancer cell phototherapy and viral or bacterial inactivation by selective nanobubble cavitation in water. [31-33] In fact, the pronounced absorption at the nanoscale in both cases reduces significantly the threshold for permanent modification, i.e., phase explosion [34] and cavitation via shock waves, produced by temperature gradients. [12,31,35] Knowledge of the minimum energy required to damage the droplet is relevant for high-repetition rate optical communications (e.g., fog clearing), [11,12] for laser spectroscopy, [2,3] and for biomedical applications (e.g., surface cleaning or airborne virus detection and inactivation in the respiratory drople...

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Section: Resultsmentioning

confidence: 99%

Tunable Near‐ to Far‐Infrared Optical Breakdown in Nonlinear Interactions of Ultrashort Laser Pulses with Water Microdroplets in Ambient Air

Rudenko

Moloney

2020

Advanced Photonics Research

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“…Indeed, in the 10 µm, picosecond pulse filamentation experiment reported in Ref. 19, no full ionization of air related to the optical breakdown was claimed-as was reported in earlier ∼100 ns CO 2 laser atmospheric breakdown experiments [21][22][23] . To explain picosecond 10 µm filamentation, it is therefore imperative to understand the role of avalanche or collisional ionization as a process that can generate a sufficient number of free carriers in air required for plasma defocusing to balance the Kerr self-focusing and create conditions for guided beam propagation.…”

Section: Introductionmentioning

confidence: 85%

“…Recent simulations have suggested that aerosols may assist in the selfguiding of LWIR pulses through the air 18 . Also, for such a CO 2 laser filament in the atmosphere, the measured average clamped intensity was ∼1 TW/cm 2 , more than an order of magnitude smaller than the so called barrier suppression threshold of O 2 /N 2 19,20 where the tunnel ionization probability becomes unity. Note that by definition the plasmadensity in such air filaments must be far below the critical density for the laser pulse that is being guided.…”

Section: Introductionmentioning

confidence: 89%

Observation of breakdown wave mechanism in avalanche ionization produced atmospheric plasma generated by a picosecond CO$_2$ laser

Welch,

Matteo,

Tochitsky

et al. 2022

Preprint

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Understanding the formation and long-timescale evolution of atmospheric plasmas produced by ultrashort, long wavelength IR (LWIR) pulses is an important but partially understood problem. Of particular interest are plasmas produced in air with a peak laser intensity ∼10 12 W/cm 2 , the so-called clamping intensity observed in LWIR atmospheric guiding experiments where tunneling and multi-photon ionization operative at near-IR or shorter wavelengths are inoperative. We find that avalanche breakdown on the surface of aerosol (dust) particles can act to seed the breakdown of air observed above the 200 GW/cm 2 threshold when a train of 3 ps 10.6 µm laser pulses separated by 18 ps are used. The breakdown first appears at the best focus but propagates backwards towards the focusing optic as the plasma density approaches critical density and makes forward propagation impossible. The velocity of the backward propagating breakdown can be as high as 10 9 cm/s, an order of magnitude greater than measured with ns pulse-produced breakdown and can be explained rather well by the so-called breakdown wave mechanism. Transverse plasma expansion with a similar velocity is assisted by UV photoionization and is observed as a secondary longitudinal breakdown mechanism in roughly 10 percent of the shots. When a cm size, TW power beam is propagated, interception of aerosol particles is guaranteed and several (40 cm −3 ) breakdown sites appear, each initially producing a near critical density plasma. On a 10 ns-1 µs timescale, shockwaves from each site expand radially and coalesce to produce a large hot gas channel. The radial velocity of the expansion agrees well with the prediction of the blast wave theory developed for ultrafast atmospheric detonations.

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“…Recent developments of ultrafast, ultrabroadband highpower laser sources operating in the mid-infrared (mid-IR,~2-15 µm) have been motivated by applications in unexplored wavelength regimes of strong-field physics [1,2] and nonlinear beam propagations [3,4] . Mid-IR laser filamentation has attracted significant attention owing to the capability of multi-octave-spanning supercontinuum generation (SCG) [5][6][7][8] , the high-energy pulse propagation with wavelength scaled (~λ 2 ) critical power, and the spectral coverage of molecular fingerprints region [9,10] .…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, it is very attractive to directly drive laser filamentation using a mid-IR laser that is free of OPA/OPCPA. For example, high-energy megafilamentation at the wavelength of~10 µm in air, pumped by a terawatt (TW)-class picosecond CO 2 laser, has been reported very recently [4] . Ultrafast mid-IR solid-state lasers based on transition-metal-doped II-VI semiconductors [14] as a host medium are also attracting great attention because they enable the high-power laser development in wavelength range of 1.8-6 µm in relatively simple, compact, and robust laser configurations similar to those of ultrafast near-IR lasers.…”

Section: Introductionmentioning

confidence: 99%

Multi-octave-spanning supercontinuum generation through high-energy laser filaments in YAG and ZnSe pumped by a 2.4 μm femtosecond Cr:ZnSe laser

Nam

Nagar

Dempsey

et al. 2021

High Pow Laser Sci Eng

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We present experimental and numerical investigations of high-energy mid-infrared filamentation with multi-octave-spanning supercontinuum generation (SCG), pumped by a 2.4 μm, 250 fs Cr:ZnSe chirped-pulse laser amplifier. The SCG is demonstrated in both anomalous and normal dispersion regimes with YAG and polycrystalline ZnSe, respectively. The formation of stable and robust single filaments along with the visible-to-mid-infrared SCG is obtained with a pump energy of up to 100 μJ in a 6-mm-long YAG medium. To the best of the authors’ knowledge, this is the highest-energy multi-octave-spanning SCG from a laser filament in a solid. On the other hand, the SCG and even-harmonic generation based on random quasi-phase matching (RQPM) are simultaneously observed from the single filaments in a 6-mm-long polycrystalline ZnSe medium with a pump energy of up to 15 μJ. The numerical simulations based on unidirectional pulse propagation equation and RQPM show excellent agreement with the measured multi-octave-spanning SCG and even-harmonic generation. They also reveal the temporal structure of mid-infrared filaments, such as soliton-like self-compression in YAG and pulse broadening in ZnSe.

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Long-wave Infrared Megafilaments in Air

Cited by 5 publications

References 3 publications

Tunable Near‐ to Far‐Infrared Optical Breakdown in Nonlinear Interactions of Ultrashort Laser Pulses with Water Microdroplets in Ambient Air

Tunable Near‐ to Far‐Infrared Optical Breakdown in Nonlinear Interactions of Ultrashort Laser Pulses with Water Microdroplets in Ambient Air

Observation of breakdown wave mechanism in avalanche ionization produced atmospheric plasma generated by a picosecond CO$_2$ laser

Multi-octave-spanning supercontinuum generation through high-energy laser filaments in YAG and ZnSe pumped by a 2.4 μm femtosecond Cr:ZnSe laser

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