Single-cycle THz signal accompanying laser wake in photoionized plasmas

Kalmykov, Serguei Y.; Englesbe, Alexander; Elle, Jennifer; Schmitt-Sody, Andreas

doi:10.1088/1361-6587/ab73db

Cited by 6 publications

(33 citation statements)

References 43 publications

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“…With nanosecond-temporal and micrometer-spatial offsets of the pre-pulse irradiation under the double pulse excitation to a tilted water flow, THz emission can be finely controlled in its intensity and polarization. This geometry verifies the theoretically-predicted coupling in under-dense gaseous plasmas at ∼ 10 17 W/cm 2 [9]. As one possible hypothesis, we have discussed a mechanism on the basis of the transverse (𝑡) plasma density gradient ∇𝑛 (𝑡) 𝑒 (water ablation by the pre-pulse irradiation) which is coupled with the longitudinal (𝑙) electron velocity in the Langmuir plasma wave v (l) p (of the main pulse).…”

Section: Introductionsupporting

confidence: 77%

“…7(b)), electrons will be pushed back (an opposite direction of the wave-field-induced electron transport). It was predicted theoretically that circularly-polarised THz emission will result from such coupling ∇𝑛 𝑒 × v p [9,18,19] and the polarization handedness depends on the sign of the cross-product. Change of the sign of v p depends on the geometrical location of the pre-pulse and the geometrical structure of the wake-field.…”

Section: Double Pulse Excitation: Pre-pulse Spatial Offsetmentioning

confidence: 99%

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Spatio-Temporal Control of THz Emission

Huang

Juodkazis

Gamaly

et al. 2022

Preprint

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Polarization fine control of THz emission is demonstrated with a tilted micro-thin water flow by the irradiation of two cross-linearly-polarized femtosecond laser pulses (800 nm, 35 fs, transform-limited) with spatio-temporal offsets. With an optimized horizontal offset at ∼ 11 𝜇m between the ∼ 8 𝜇m focal spots and time delay at 4.7 ns, circularly-polarized THz emission was obtained with its intensity enhancement more than 1,500-times if compared with the single pulse irradiation. It is shown that the photon-number-based efficiency from the laser to THz at 7.1x10^−3 is achieved with the optimisation of the double pulse irradiation. Polarization-resolved THz time-domain spectroscopy and time-resolved shadowgraphy imaging revealed that the circularly-polarized THz emission originates from the focal volume in front of the water flow. Coupling between a shockwave due to air-breakdown and water ablation-mediated mass transport by the first pulse with a laser wake-field along the optical path of the main pulse is responsible for the point-like single-cycle THz source.

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Section: Introductionsupporting

confidence: 77%

Section: Double Pulse Excitation: Pre-pulse Spatial Offsetmentioning

confidence: 99%

Spatio-Temporal Control of THz Emission

Huang

Juodkazis

Gamaly

et al. 2022

Preprint

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show abstract

“…7b), electrons will be pushed back (an opposite direction of the wave-field-induced electron transport). It was predicted theoretically that circularly-polarised THz emission will result from such coupling ∇ n e × v p 15,22,23 and the polarisation handedness depends on the sign of the cross-product. Change of the sign of v p depends on the geometrical location of the pre-pulse and the geometrical structure of the wake-field.…”

Section: Discussionmentioning

confidence: 99%

“…The maximum of THz emission was observed at Δx = 11 μm offset under the optimised (Δt = 4.7 ns) double pulse exposure with the diameter of the focal spot at ~8 μm. Maximising the plasma density gradient ∇n ðtÞ e (transverse) coupling with electron velocity v ðlÞ e (longitudinal) is required for the generation of the circular current 15 . Formation of the electron density gradient ∇ n e (transverse) facilitates induction of a rotational current ∇ × j = e ∇ n e × v ≠ 0, where v is the longitudinal electron velocity in the wake, hence, ∇ × v ≡ 0 22 (see Supplementary Note 3 and Fig.…”

Section: Discussionmentioning

confidence: 99%

Spatio-temporal control of THz emission

et al. 2022

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Intense THz sources are expected for further progresses in nonlinear THz science and technology. Liquids like water are durable and continuously-reusable under intense laser irradiation for THz emission though such studies on THz emission from water targets are so far limited. Polarisation fine control of THz emission is demonstrated with a tilted micro-thin water flow by the irradiation of two cross-linearly-polarised femtosecond laser pulses (800nm, 35fs, transform-limited) with spatio-temporal offsets. With an optimized horizontal offset at ∼11 μm between the ∼8 μm focal spots and time delay at 4.7ns, circularly-polarised THz emission is obtained with its intensity enhancement more than 1,500-times if compared with the single pulse irradiation. It is shown that the photon-number-based efficiency from the laser to THz at 7.1 x 10−3 is achieved with the optimisation of the double pulse irradiation. Polarisation-resolved THz time-domain spectroscopy and time-resolved shadowgraphy imaging reveal that the circularly-polarised THz emission originates from the focal volume in front of the water flow. Coupling between a shockwave due to air-breakdown and water ablation-mediated mass transport by the pre-pulse with a laser wake-field along the optical path of the main pulse is responsible for the point-like single-cycle THz emission.

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“…(3D) Langmuir wave excitation in the region of plasma inhomogeneity. One physical concept to support this notion is linear mode conversion, from electrostatic Langmuir to transverse magnetic (TM), in the vicinity of the critical surface [5][6][7][8][9][10][11]. The other concept builds upon the fact that the USPL-driven plasma wave (a 'laser wake' with a relativistic phase velocity [12][13][14][15]) is not purely electrostatic in the nonhomogeneous plasma.…”

Section: Introductionmentioning

confidence: 99%

Reversal of laser wake phase velocity generates high-power broadband Cherenkov signal

Kalmykov

Elle

Schmitt-Sody

2021

Plasma Phys. Control. Fusion

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As a femtosecond terawatt laser pulse propagates along a positive density gradient within a stratified plasma column, it drives a low-frequency electromagnetic wake wave, the period of electron fluid oscillations in the wake gradually shrinking. Phase velocity of the wake promptly exceeds the vacuum speed of light, setting in near-forward emission of terahertz Cherenkov radiation. As the wake accelerates further, the Cherenkov emission ray rotates by 180∘. Emission from a given plasma locality is sustained for a finite interval of time, in the middle of which the wake experiences a ‘reversal,’ its phase velocity becoming singular and changing sign (Zhang C J et al 2017 Phys. Rev. Lett. 119 064801) At this instant, the electromagnetic energy flows at 90∘, the emission power reaching its peak. After the reversal, the wake keeps radiating into the rear hemisphere until its phase velocity becomes subluminal. Experimentally capturing evolution of the Cherenkov signal may thus shed light onto the plasma wake dynamics. Far away from the plasma, the radiation fills an expanding, almost spherical shell, the shell thickness increasing with an increase in the observation angle. The length of the terahertz signal sampled in the wave zone thus ranges from zero (forward emission) to a few tens of picoseconds (backward emission). The signal is positively chirped, its frequency increasing from the Langmuir frequency at the foot of the column to the Langmuir frequency at the top. Theoretical estimates for the regimes involving 10 TW-class drive pulses promise a few-kW emission power; the energy conversion efficiency, from optical to terahertz, of order 10−7; and an MV m−1-scale electric field strength centimeters away from the plasma.

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Single-cycle THz signal accompanying laser wake in photoionized plasmas

Cited by 6 publications

References 43 publications

Spatio-Temporal Control of THz Emission

Spatio-Temporal Control of THz Emission

Spatio-temporal control of THz emission

Reversal of laser wake phase velocity generates high-power broadband Cherenkov signal

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