Haut PDF Terahertz Radiation from Laser Induced Plasmas

Terahertz Radiation from Laser Induced Plasmas

Terahertz Radiation from Laser Induced Plasmas

HAL Id: hal-01545493 https://hal.archives-ouvertes.fr/hal-01545493 Submitted on 22 Jun 2017 HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

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Dynamics of UV short pulse laser-induced plasmas from a ceramic material “titanium carbide”: a hydrodynamical out of equilibrium investigation

Dynamics of UV short pulse laser-induced plasmas from a ceramic material “titanium carbide”: a hydrodynamical out of equilibrium investigation

4 describe the ablation process as a whole through a thermal model for the pulse-target interaction coupled with an out of equilibrium model for the plasma formation and expansion. In a previous work (Ait Oumeziane et al. 2016a) we investigated the ablation process under the same conditions of two metals namely titanium and copper. A comparison between target melting and evaporation thresholds where presented along with ablation depths and plasma ignition thresholds. Results for both materials differ considerably. Those discrepancies have been linked to the targets properties especially their thermal conductivity which has been shown to be the one governing the ablation process. More recently we have developed a new model to describe the ablation process of a multicomponent target (Ait Oumeziane and Parisse 2018). The latter has been applied to titanium carbide (TiC) with a focus on comparing processes in the material such as melting and ablation depths and thresholds as well as plasma shielding rates induced under the same conditions from a pure titanium material. Plume electronic and heavy species temperatures and densities have also been presented and the thermal no equilibrium investigated. However, in this preliminary study the plasma dynamic has not the center of interest. The present paper is dedicated to investigating the dynamic of laser induced plasmas from a ceramic material. To have a better understanding of the link between the material properties and the plume characteristics and dynamic, a thorough examination of the entire ablation processes is made. Results comparison with the behavior of laser induced plumes under the same conditions from a pure material is shown to have a key role in shedding the light on what monitors the plume expansion in the background environment. Plume temperatures, velocities, ionization rates as well as elemental composition have been presented and compared under carefully chosen relevant conditions which will be defined later.
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Terahertz emission from laser-driven gas-plasmas: a plasmonic point of view

Terahertz emission from laser-driven gas-plasmas: a plasmonic point of view

6 Institut Lumière Matière, UMR 5306 Université Lyon 1 —CNRS, Université de Lyon, 69622 Villeurbanne, France *Corresponding author: illia-thiele@web.de Received 11 September 2018; revised 19 November 2018; accepted 19 November 2018 (Doc. ID 345671); published 20 December 2018 We disclose an unanticipated link between plasmonics and nonlinear frequency down-conversion in laser-induced gas- plasmas. For two-color femtosecond pump pulses, a plasmonic resonance is shown to broaden the terahertz emission spectra significantly. We identify the resonance as a leaky mode, which contributes to the emission spectra whenever electrons are excited along a direction where the plasma size is smaller than the plasma wavelength. As a direct con- sequence, such resonances can be controlled by changing the polarization properties of elliptically shaped driving laser pulses. Both experimental results and 3D Maxwell consistent simulations confirm that a significant terahertz pulse shortening and spectral broadening can be achieved by exploiting the transverse driving laser beam shape as an addi- tional degree of freedom. © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement https://doi.org/10.1364/OPTICA.5.001617
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Theory of terahertz emission from femtosecond-laser-induced micro-plasmas

Theory of terahertz emission from femtosecond-laser-induced micro-plasmas

ration established in App. A 2 . VI. SUMMARY AND CONCLUSION We have analyzed the emission of broadband THz ra- diation from femtosecond laser-induced gas plasmas by means of theoretical modeling and numerical simulations. Our approach is based on a multiple scale analysis of the non-relativistic Vlasov equation, which allows us to iden- tify distinct THz generation mechanisms. We have ob- tained closed systems of equations describing the ioniza- tion current (IC) [ 11 ] as well as the transition-Cherenkov (TC) [ 13 ] mechanism. Both mechanisms have been dis- cussed already in the literature, but usually without a di- rect comparison. Our model accounts for, among others, field ionization, damping of the current due to collisions, and heating of the electron plasma. Plasma currents can be excited due to the electric laser field (IC) as well as ponderomotive, radiation pressure, convective and diffu- sive sources (TC). Confrontation of the model with rig- orous PIC simulations shows excellent agreement. The main results of this paper are as follows.
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Strong Enhancement of Terahertz Radiation from Laser Filaments in Air by a Static Electric Field

Strong Enhancement of Terahertz Radiation from Laser Filaments in Air by a Static Electric Field

This is a typical damped oscillation at the plasma frequency. The on-axis amplitude is proportional to the filament length and the plasma density, and the cone opening is a few degrees for the present parameters. The analysis of the far field THz emission provides a method for measuring the ponderomotive potential (or the laser intensity in the filament). For a low DC field, the THz field generated by the ponderomotive force, E 1 is comparable with the one induced by the static transverse field E 2 . By observing the far field angular pattern resulting from their superposition, one can estimate the relative strength of the two fields, and deduce the ponderomotive potential of the laser pulse responsible for the transition Cerenkov emission. The Fourier components of the two radiation electric fields at the distance r from the filament within the emission cone read:
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Resonant Effects in Terahertz Generation with Laser-Induced Gas Plasmas

Resonant Effects in Terahertz Generation with Laser-Induced Gas Plasmas

Resonant Effects in Terahertz Generation with Laser-Induced Gas Plasmas I. Thiele 1,2 , B. Zhou 3 , A. Nguyen 4 , E. Smetanina 1,5 , R. Nuter 1 , P. González de Alaiza Martínez 1 , K. J. Kaltenecker 3 , J. Déchard 4 , L. Bergé 4 , P. U. Jepsen 3 , and S. Skupin 1,6 1 Univ. Bordeaux - CNRS - CEA, Centre Lasers Intenses et Applications, Talence, France 2 Department of Physics, Chalmers University of Technology, Göteborg, Sweden

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Terahertz spectroscopy from air plasmas created by two-color femtosecond laser pulses: The ALTESSE project

Terahertz spectroscopy from air plasmas created by two-color femtosecond laser pulses: The ALTESSE project

Terahertz spectroscopy from air plasmas created by two-color femtosecond laser pulses: The ALTESSE project L. Berg´ e 1 , K. Kaltenecker 2 , S. Engelbrecht 3 , A. Nguyen 1 , S. Skupin 4 , L. Merlat 3 , B. Fischer 3 , B. Zhou 2 , I. Thiele 5 and P. U. Jepsen 2 1 CEA, DAM, DIF - 91297 Arpajon - France

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Broadband terahertz emission from two-color femtosecond-laser-induced microplasmas

Broadband terahertz emission from two-color femtosecond-laser-induced microplasmas

Terahertz (THz) sources are essential for various appli- cations such as imaging and time-domain spectroscopy or control of matter by THz waves [ 1 – 3 ]. A promising ap- proach to generate broadband THz radiation is to employ laser-induced gas plasmas [ 4 , 5 ]. Spectral properties and the absence of irreversible material damage make them interesting alternatives to conventional THz sources such as photo-conductive switches or quantum cascade lasers. In order to miniaturize such THz sources, it has been proposed to exploit laser-induced microplasmas [ 6 ] that allow to use smaller driving lasers. Such microplasmas are created when a fs-laser pulse is focused tightly, down to the diffraction limit, into a gas. The strong focusing leads to laser intensities above 10 14 W/cm 2 already for
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Broadband terahertz radiation from two-color mid- and far-infrared laser filaments in air

Broadband terahertz radiation from two-color mid- and far-infrared laser filaments in air

are indicated by gray lines. creasing the pump wavelength, longer filaments form (see also [27]). Due to the smaller Rayleigh range, the 10.6- µm pump pulse starts its self-focusing sequence earlier. Figure 1(e) illustrates the THz energy inside part of the numerical box versus the propagation axis. This energy remains below the µJ level for λ0 = 0.8 µm, but it in- creases to the 0.1 mJ level for mid-IR pumps and even to 3.1 mJ for far-IR lasers, confirming the 4 orders of magnitude increase expected from the LC model above. The THz CE obtained at 10.6 µm is 3% against 1% at 3.9 µm. Let us notice that the yield curves of Fig. 1(e) decrease instead of saturating to a plateau value, which is mainly due to THz components leaving our finite time window.
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Plasmonic Resonances Affecting Terahertz Generation in Laser-Induced Gas-Plasmas

Plasmonic Resonances Affecting Terahertz Generation in Laser-Induced Gas-Plasmas

HAL Id: hal-01924405 https://hal.archives-ouvertes.fr/hal-01924405 Submitted on 15 Nov 2018 HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

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Direct modulation and bandwitdh measurement of terahertz quantum cascade laser

Direct modulation and bandwitdh measurement of terahertz quantum cascade laser

Keywords: Bandwidth measurement, Quantum Cascade Laser, Modulation, Modelling 1. INTRODUCTION This paper aims at proposing a theoretical description of small signal modulation of Quantum Cascade Lasers (QCL). Their invention in 1994 by Faist, Capasso et al. 1 brought a powerful and compact solid source of far infrared radiation. Since then, their performances have continuously improved. Terahertz QCL working above liquid nitrogen temperature, 2, 3 and even at room temperature by intracavity difference-frequency generation, have been reported. 4 Their spectral range is now extending from the mid-infrared down to 1.2 THz. 5 Due to the novel properties and unique interaction with many materials, the terahertz radiation has become a topic of active research for the past few years, and is still a going concern. 6, 7 Among the large possibilities of applications, free space short range communications have been studied 8, 9 because of the Wi-Fi capabilities of terahertz waves and QCL large supposed bandwidth modulation. 10 QCL-based local oscillators are also attractive for radioastronomy applications 11 thanks to their high spectral purity, adequate output power and good stability. Modeling the behavior of QCLs is therefore an important step toward the prediction of performances of such semi-conductor sources. Microscopic modelings have proved to be relevant in predicting and analyzing quantum device carrier dynamics and have largely participate to their design improvement. 12, 13
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Coherent control of boosted terahertz radiation from air plasma pumped by femtosecond three-color sawtooth field

Coherent control of boosted terahertz radiation from air plasma pumped by femtosecond three-color sawtooth field

5. Conclusion In conclusion, we demonstrated a simple and robust inline optical setup enabling precise control of the relative phases between three harmonic femtosecond laser fields, providing a sawtooth- like wave. It is based on the widely available femtosecond laser pulses at 800 nm. It was observed that the THz radiation amplitude produced in air with this phase-optimized three-color sawtooth-like wave is enhanced by 80% compared to that produced with two-color laser fields. The coherent control of azimuth angle, the polarity and amplitude of the enhanced THz pulse through a variation of the relative phases Δ or Δ of the three-color fields is in good agreement with the transient electron current model. Well controlled production of intense THz pulses of ultrashort duration (close to a single cycle pulse) and concomitant broadband spectrum should be beneficial for ultrafast dynamics application in the THz domain. Moreover, this simple and robust 3-color optical field synthesizer with attosecond precision can find wide applications in the domain of femtosecond laser-material interaction, such as high-order harmonic generation [ 34, 35 ], generation of white-light continuum in the mid-IR and UV regime [ 36-38 ], and field- free molecule alignment and orientation [ 39 ], where three-color femtosecond pulse excitation has been found to be much more efficient and beneficial.
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Terahertz radiation for the characterization of plasmonic nanoparticles and its biomedical applications.

Terahertz radiation for the characterization of plasmonic nanoparticles and its biomedical applications.

4 CONCLUSION Photoexcitation of light-sensitive agents, such as nanoparticles (NPs) introduced into the human body, can affect biological tissue and cells in various ways. Chemical reactions (photochemical), biological processes (photobiological), as well as heat (photothermal) can be triggered by light. Optical therapy utilizes these effects in a controlled fashion, for example, photothermal therapy (PTT) aims to induce photothermal effects based on the principle that the local temperature of tissue increases as a result of laser absorption. PTT, as a minimally invasive treatment option, is foreseen to make its most substantial impact on the destruction of cancerous tumor cells in a controllable, spatially confined, and selective way to minimize collateral tissue damage by employing photothermal agents, such as NPs. Cancer has been one of the significant threats to human health for centuries, and according to the International Agency for Research on Cancer (IARC) report, the global casualty rate and new cases of cancer-related diseases in 2018 amounted to 9.6 million and 18.1 million worldwide, respectively [183]. Extensive research efforts have been directed towards improved synthesis strategies to design multimodal nanomaterials with tumor-targeting as well as highly efficient heating properties. Hence, the accurate determination of the photothermal response of nanomaterials represents an essential aspect of PTT treatments that can be used to achieve the desired temperature-induced effects in cancerous tissue. However, even nowadays, the quantification of the photothermal conversion efficiency (PCE) has not been adequately addressed by current methods, such as thermocouples, infrared (IR) thermometers, and IR thermography. They are either invasive and could potentially contaminate the fragile ecosystem of the NP dispersion or cannot measure the temperature beyond-line-of-sight directly at the interface where the photothermal excitation of the NP dispersion occurs. In this thesis, these challenges were addressed by a novel method for the characterization of the photothermal effect of NPs in aqueous NP dispersions, carried out in a non-contact and non-invasive manner to be implemented in a typical THz time-domain- spectroscopy (THz-TDS) system.
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Wavelength scaling of terahertz pulse energies delivered by two-color air plasmas

Wavelength scaling of terahertz pulse energies delivered by two-color air plasmas

Knowing the great sensitivity of THz emitters with respect to the interaction conditions, we can wonder whether the seem- ingly contradiction between a λ 2 scaling expected from pho- tocurrents and the steeper increase reported in [3, 10] follows from inconsistencies in the beam spatial diameters and pulse du- rations that may vary a lot in OPAs [ 11 ]. Moreover, the relative phase between FH and SH fields has a strong impact on the THz energy [ 2 ]. It cannot be directly monitored in experiments, but may change the THz yield by half an order of magnitude (see, e.g., Fig. 5 of [ 4 ]). Thus, revisiting the wavelength scaling of the THz energy while keeping an eye on both the laser parameters and the value of this phase offset appears timely .
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Generation of intense terahertz sources by ultrashort laser pulses

Generation of intense terahertz sources by ultrashort laser pulses

First of all, the experimental setup is described 1 . In the experiment a 800-nm beam supplied by a Ti:sapphire regenerative amplifier 2 is focused with a f = 15 cm plano-convex lens into ambient air [Fig. 4.1.1 (a)]. A 0.1-mm-thick beta barium borate (β-BBO) crystal (I type) adjusted to reach the maximum THz yield is used for generating the second har- monic. A 1.5-cm laser spark formed near the geometrical focus locates the emitted THz radiation, which is collimated using an off-axis parabolic mirror (51.6 mm in diameter and 150-mm effective focal length). A 0.35-mm-thick silicon wafer filters the radiated field. To investigate the frequency-angular terahertz spectrum, a Michelson interferometer is coupled to a liquid helium-cooled silicon bolometer LN-6/C 3 , used as a detector of the THz radiation. A 3.5-mm-thick high-resistive silicon beam splitter 4 with 50-mm aperture is employed for separation and recombination of the two arms of the interferometer end- ing with flat metallic mirrors, one of which is placed on a motorized translation stage. After recombination, the THz beam is refocused with an off-axis parabolic mirror into the aperture of the bolometer with filters transparent in the THz region (e.g., < 24 THz). Typical interferograms have 500-800 points with 2.5-µm increment ensuring spectral res- olution up to 75 GHz. The reconstruction of the THz spectrum is done using the Fourier transform of the THz signal autocorrelation function. THz spectra recorded from 50 averaged interferograms have been obtained using 1.4-mJ, 130-fs two-colour pulses with ∼ 10% fraction of second harmonic in amplitude. The resulting THz field is displayed in
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Towards compact efficient fs-laser-induced THz sources from microplasmas

Towards compact efficient fs-laser-induced THz sources from microplasmas

In the strongest focusing case, the only 10-µm-long microplasma acts as a point-like source for THz wave- lengths. Its torus-shaped radiation profile is sketched in Fig. 1 (a-b), where the fundamental harmonic (FH) and second harmonic (SH) electric fields are parallelly resp. perpendicularly polarized relative to each other. The polar- ization of the SH field with respect to the FH field determines the polarization of the THz radiation and the emission profile. Increasing the plasma length as illustrated in Fig. 1 (c) leads to a more forward directed THz emission, consistent with what one would expect when changing from a point to a line source. Such longer, forward emitting plasma produces an almost isotropic emission cone (not shown here). The total amount of the produced electron charge Q and thus potential THz emitters increases rapidly with w 0 , as depicted in Fig. 1 (d). This increase of the
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Short-pulse laser-produced plasmas

Short-pulse laser-produced plasmas

In the 80s, advances in laser science and optical technologies have opened new possibilities in the study of laser-produced plasmas. One of these advances is the implementation of the Chirped Pulse Amplification (CPA) technique [1] which has created new opportunities in the domain of ultra-intense and ul- trafast laser physics. The interactions of ultra high-intensity laser pulses with matter have opened the field of optics in relativistic plasmas, a new topic of high-field science presented in comprehensive reviews [2, 3]. Indeed, intense lasers have been used to accelerate beams of electrons [4] and protons [5] to energies of several megaelectronvolts in distances of only microns. Recent improvements in particle energy spread [6] may allow compact laser-based radiation sources to be useful someday for cancer hadrontherapy [7] and as injectors into conventional accelerators [8], which are critical tools for x-ray and nuclear physics research. They might also be used for “fast ignition” [9] of inertial fusion targets. The ultrashort pulse duration of these particle bursts and the x rays they can produce, hold great promise as well to resolve chemi- cal, biological or physical reactions on ultrafast time scales and on the spatial scale of atoms [10]. Indeed, the time duration of these pulses being less than 100-fs, this is shorter than the time-scale of significant hydrodynamic motion of ions or solid target surfaces. Consequently, solid-density matter may be heated from room temperature to several hundreds of electronvolts without the usual change in density that accompanies long-pulse irradiation [11]. Ul- trafast plasmas have important applications in material processing [12], thin film growth using ultrafast pulsed-laser deposition [13], and ultrashort pulse x-ray sources [14].
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New Journal of Physics Mechanisms of forward laser harmonic emission from thin overdense plasmas

New Journal of Physics Mechanisms of forward laser harmonic emission from thin overdense plasmas

distributions ( J y (x, t) in the boosted frame) in these two cases. high frequencies in the light spectrum: this effect thus corresponds to the usual Doppler upshift induced by a relativistic motion of the radiation source toward the observation point. Figure 6 reveals an obvious, yet essential, feature of the Doppler effect, namely that it leads to an electromagnetic field that strongly depends on the observation direction: when the current distribution at the plasma surface moves toward vacuum, a frequency upshift occurs in the direction of the reflected beam, but not in the opposite direction. A similar process might however lead to forward attosecond pulse emission when the current distribution moves toward
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Amplification of transition-Cherenkov terahertz radiation of femtosecond filament in air

Amplification of transition-Cherenkov terahertz radiation of femtosecond filament in air

of the ionization front 8 . Recently, it was demonstrated that by applying a transverse electric field (with respect to the filament axis), it is possible to enhance the THz emission intensity by at least 3 orders of magnitude 9 . In this paper, we follow this idea and demonstrate that the intensity of the THz emission from laser filament is enhanced by three orders of magnitude if one applies a static electric field along the filament axis. In contrast to the case with a transverse field, the angular radiation pattern and the polarization characteristics of the THz wave remain the same as those without the external electric field. We extend the transition- Cherenkov model by taking into account the electron current in filament driven by the external voltage. This model reproduces all the observed features of this amplified THz emission.
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Space and time characterization of laser-induced plasmas for applications in chemical analysis and thin film deposition

Space and time characterization of laser-induced plasmas for applications in chemical analysis and thin film deposition

74 In order to quantify the importance of confinement and its role in the plasma behaviour, we have estimated the total number of electrons, N, in the plasma in various experimental conditions. This number is determined by multiplying the measured electron density by the plasma volume estimated from its shape (hemispherical, conical, etc.), its radial extension and its length. Figures (3-7a to 7c) show the results obtained as a function of pressure for two different delays after laser shots and for the three ambient gases investigated. Interestingly, one clearly sees that in a first approximation, N nearly constant with rising pressure and almost independent of the gas type. These two observations undoubtedly indicate that plasma expansion is fully inhibited by the presence of the ambient gas when the pressure increases. It also means that the creation of the plasma is not influenced by its environment at time delay < 200 ns. As expected, at time delay 500 ns, N decreases with time delay after laser shots, which is simply due to recombination. Detailed observations suggest a slight decrease of N at atmospheric pressure. This may indicate a stronger interaction between the plume and the gas at higher pressures. However, we have to be careful since the volume was roughly estimated so that it may happen that these variations may not be significant.
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