Quantitative measurement of electron number in nanosecond and picosecond laser-induced air breakdown

Wu, Yue; Sawyer, Jordan C.; Liu, Su

doi:10.1063/1.4948431

Cited by 27 publications

(23 citation statements)

References 25 publications

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“…A 10-dBm tunable microwave source (HP 8350B sweep oscillator, set at ~10 GHz) was split into two channels [22,24]. One of the channels was used to illuminate the plasma by employing a microwave horn (WR75, 15-dB gain).…”

Section: Coherent Microwave Scattering Systemmentioning

confidence: 99%

“…Microwave scattering can measure the total electron number evolution with a temporal resolution of ~3 nanoseconds (ns). Note that plasma expansion leads to a critical electron number density beyond the microwave penetration depth, which causes the microwave signal to decrease after peak [22]. A variable zoom camera lens was used to relay the plasma emissions into the threechannel MUSIC apparatus, as shown in Fig.…”

Section: Imaging Targetmentioning

confidence: 99%

“…Emissions from laser-induced plasmas are initially broadband continuum as inverse bremsstrahlung and free-free transitions . The emissions become distinct atomic emission lines after the plasma cools down at 20 -30 ns [22]. Coherent microwave scattering tracks total electron number in the plasma and is proportional to the total plasma emissions in the avalanche phase of the plasma generation.…”

Section: Comparisons With Coherent Microwave Scattering and Plasma Momentioning

confidence: 99%

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Single-shot nanosecond-resolution multiframe passive imaging by multiplexed structured image capture

et al. 2018

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The Multiplexed Structured Image Capture (MUSIC) technique is used to demonstrate single-shot multiframe passive imaging, with a nanosecond difference between the resulting images. This technique uses modulation of light from a scene before imaging, in order to encode the target's temporal evolution into spatial frequency shifts, each of which corresponds to a unique time and results in individual and distinct snapshots. The resulting images correspond to different effective imaging gate times, because of the optical path delays. Computer processing of the multiplexed single-shot image recovers the nanosecondresolution evolution. The MUSIC technique is used to demonstrate imaging of a laserinduced plasma. Simultaneous single-shot measurements of electron numbers by coherent microwave scattering were obtained and showed good agreement with MUSIC characterization. The MUSIC technique demonstrates spatial modulation of images used for passive imaging. This allows multiple frames to be stacked into a single image. This method could also pave the way for real-time imaging and characterization of ultrafast processes and visualization, as well as general tracking of fast objects.

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Section: Coherent Microwave Scattering Systemmentioning

confidence: 99%

Section: Imaging Targetmentioning

confidence: 99%

Section: Comparisons With Coherent Microwave Scattering and Plasma Momentioning

confidence: 99%

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Single-shot nanosecond-resolution multiframe passive imaging by multiplexed structured image capture

et al. 2018

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“…A careful understanding of electromagnetic-plasma and scattering interactions is essential for the proper extraction of information on total electron numbers and subsequent derivable quantities (e.g., the electron number density ) from CMS. Vast historical art exists for weakly-ionized, strongly collisional microplasmas in which electron motion is restricted by electron-neutral collisions 4 , 5 , 9 , 10 . However, application of the diagnostic to collisionless plasmas has remained relatively unexplored (no N e correspondence is given by 11 , 13 , 18 )—despite garnering some attention in recent years 19 due to a prevalence in studies on electric propulsion devices 20 , photoionization in low-pressure conditions 21 , 22 , etc.…”

Section: Introductionmentioning

confidence: 99%

Thomson and collisional regimes of in-phase coherent microwave scattering off gaseous microplasmas

Patel

Ranjan

Wang

et al. 2021

Sci Rep

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The total number of electrons in a classical microplasma can be non-intrusively measured through elastic in-phase coherent microwave scattering (CMS). Here, we establish a theoretical basis for the CMS diagnostic technique with an emphasis on Thomson and collisional scattering in short, thin unmagnetized plasma media. Experimental validation of the diagnostic is subsequently performed via linearly polarized, variable frequency (10.5–12 GHz) microwave scattering off laser induced 1–760 Torr air-based microplasmas (287.5 nm O2 resonant photoionization by ~ 5 ns, < 3 mJ pulses) with diverse ionization and collisional features. Namely, conducted studies include a verification of short-dipole-like radiation behavior, plasma volume imaging via ICCD photography, and measurements of relative phases, total scattering cross-sections, and total number of electrons $$N_{e}$$ N e in the generated plasma filaments following absolute calibration using a dielectric scattering sample. Findings of the paper suggest an ideality of CMS in the Thomson “free-electron” regime—where a detailed knowledge of plasma and collisional properties (which are often difficult to accurately characterize due to the potential influence of inhomogeneities, local temperatures and densities, present species, and so on) is unnecessary to extract $$N_{e}$$ N e from the scattered signal. The Thomson scattering regime of microwaves is further experimentally verified via measurements of the relative phase between the incident electric field and electron displacement.

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“…16 In traditional ns-LIBS, the plasma results from a few seed electrons being generated via multiphoton ionization at a high-intensity focus of the laser beam; these seed electrons are then accelerated by the pervading laser field to liberate more electrons. 3,4,17,18 This process, termed avalanche ionization, leads to a strong plasma with continuum radiation dominating the early emission and atomic emission emerging as the plasma rapidly expands and cools down. The continuum radiation, a trademark of the avalanche ionization process, is generally problematic for accurate measurements of equivalence ratio.…”

Section: Introductionmentioning

confidence: 99%

Time-Gated Single-Shot Picosecond Laser-Induced Breakdown Spectroscopy (ps-LIBS) for Equivalence-Ratio Measurements

et al. 2020

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Time-gated picosecond laser-induced breakdown spectroscopy (ps-LIBS) for the determination of local equivalence ratios in atmospheric-pressure adiabatic methane–air flames is demonstrated. Traditional LIBS for equivalence-ratio measurements employ nanosecond (ns)-laser pulses, which generate excessive amounts of continuum, reducing measurement accuracy and precision. Shorter pulse durations reduce the continuum emission by limiting avalanche ionization. Furthermore, by contrast the use of femtosecond lasers, plasma emission using picosecond-laser excitation has a high signal-to-noise ratio (S/N), allowing single-shot measurements suitable for equivalence-ratio determination in turbulent reacting flows. We carried out an analysis of the dependence of the plasma emission ratio Hα (656 nm)/NII (568 nm) on laser energy and time-delay for optimization of S/N and minimization of measurement uncertainties in the equivalence ratios. Our finding shows that higher laser energy and shorter time delay reduces measurement uncertainty while maintaining high S/N. In addition to atmospheric-pressure flame studies, we also examine the stability of the ps-LIBS signal in a high-pressure nitrogen cell. The results indicate that the plasma emission and spatial position could be stable, shot-to-shot, at elevated pressure (up to 40 bar) using a lower excitation energy. Our work shows the potential of using ps-duration pulses to improve LIBS-based equivalence-ratio measurements, both in atmospheric and high-pressure combustion environments.

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Quantitative measurement of electron number in nanosecond and picosecond laser-induced air breakdown

Cited by 27 publications

References 25 publications

Single-shot nanosecond-resolution multiframe passive imaging by multiplexed structured image capture

Single-shot nanosecond-resolution multiframe passive imaging by multiplexed structured image capture

Thomson and collisional regimes of in-phase coherent microwave scattering off gaseous microplasmas

Time-Gated Single-Shot Picosecond Laser-Induced Breakdown Spectroscopy (ps-LIBS) for Equivalence-Ratio Measurements

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