Interaction Of Intense Laser Pulses Research Articles

Interaction of intense ultrashort laser pulses with solid targets: A systematic analysis using first-principles calculations

Interaction of intense ultrashort laser pulses with solid targets: A systematic analysis using first-principles calculations

Spatiotemporal reshaping of femtosecond laser pulses on interaction with gas sheath at ionization saturation intensity regime

Interaction of intense ultrashort laser pulse with gases generates a transient spatiotemporal electron density distribution via field ionization, which may lead to the spatiotemporal reshaping of the pulse, viz., its beam profile, pulse width, etc. Here, we present an experimental study on ultrashort laser pulse interaction with argon gas sheath in an ionization saturation intensity regime (∼1015–1017 W/cm2). The present investigation has been performed using a 6 mJ, 1 kHz, and 55−60 fs Ti:Sapphire laser pulse interaction with a ∼2.5 mm long argon sheath. After the laser gas interaction, the laser spatial profile exhibits a multi-ring structure around a central maximum spot. Laser gas interaction parameters, such as laser intensity, gas pressure, etc., affect the ring pattern significantly. Under optimum parameter conditions, the laser pulse has two rings in spatial profile, and the pulse width of the central spot is self-compressed to ∼35 fs. A theoretical calculation reveals that the laser beam’s spatiotemporal profile evolves as it propagates inside the gas sheath. The calculation also demonstrates that the gas ionization profile plays a crucial role in the spatiotemporal reshaping and self-compression of the laser beam. The calculation also shows that the generation of concentric ring patterns in the spatial profile is mainly due to the ionization of argon atoms into Ar+, Ar2+, and Ar3+ species in the interaction region. Such self-compressed laser pulses with concentric ring beam profiles may be useful for high-harmonic generation and shorter attosecond pulse trains.

Investigation of terahertz radiation generation from laser-wakefield acceleration

We investigate the generation of terahertz (THz) radiation from laser-wakefield acceleration (LWFA) in a helium gas jet. We consider a three-dimensional setup incorporating a realistic gas density distribution and use particle-in-cell simulations to study the interaction of a femtosecond intense laser pulse with the gas medium. Our results show that LWFA can efficiently produce THz radiation. In the simulations, we use multiple probes to record the electric and magnetic fields arising from the interaction. In addition, we compare the results of fixed and moving window simulation boxes used to capture electromagnetic fields in the THz range. We demonstrate that a moving window with a 600 μm width can be significantly useful for THz studies. We further analyze the spectrum of spatially and temporally resolved electromagnetic radiation and its emission angle. Our results are consistent with experimental data. Our findings provide valuable insights into the potential of LWFA as a strong source of THz radiation.

Multiple-Photon Resonance Enabled Quantum Interference in Emission Spectroscopy of N2+

Quantum interference occurs frequently in the interaction of laser radiation with materials, leading to a series of fascinating effects such as lasing without inversion, electromagnetically induced transparency, Fano resonance, etc. Such quantum interference effects are mostly enabled by single-photon resonance with transitions in the matter, regardless of how many optical frequencies are involved. Here, we report on quantum interference driven by multiple photons in the emission spectroscopy of nitrogen ions that are resonantly pumped by ultrafast infrared laser pulses. In the spectral domain, Fano resonance is observed in the emission spectrum, where a laser-assisted dynamic Stark effect creates the continuum. In the time domain, the fast-evolving emission is measured, revealing the nature of free-induction decay arising from quantum radiation and molecular cooperativity. These findings clarify the mechanism of coherent emission of nitrogen ions pumped with mid-infrared pump laser and are found to be universal. The present work opens a route to explore the important role of quantum interference during the interaction of intense laser pulses with materials near multiple photon resonance.

Anomalous Relativistic Emission from Self-Modulated Plasma Mirrors.

The interaction of intense laser pulses with plasma mirrors has demonstrated the ability to generate high-order harmonics, producing a bright source of extreme ultraviolet (XUV) radiation and attosecond pulses. Here, we report an unexpected transition in this process. We show that the loss of spatiotemporal coherence in the reflected high harmonics can lead to a new regime of highly efficient coherent XUV generation, with an extraordinary property where the radiation is directionally anomalous, propagating parallel to the mirror surface. With analytical calculations and numerical particle-in-cell simulations, we discover that the radiation emission is due to laser-driven oscillations of relativistic electron nanobunches that originate from a plasma surface instability.

Intense laser pulse interaction with a nanofoil and generation of energetic protons in underdense upstream plasma

Intense laser pulse interaction with a nanofoil and generation of energetic protons in underdense upstream plasma

Betatron Radiation and Bremsstrahlung in the Interaction of Intense Laser Pulse with Solid Target

X-ray generation via synchrotron radiation and bremsstrahlung in the interaction of short laser pulses with a solid target is of much current interest owing to its numerous applications. The efficiency of laser to X-ray energy conversion is thus a crucial factor. We found that the energy conversion efficiency of synchrotron radiation and bremsstrahlung is mainly governed by the ratio of the laser pulse width to the preplasma width, which is in turn governed by the laser profile, intensity, and spot size. Synchrotron radiation dominates when the ratio is less than unity, otherwise bremsstrahlung dominates. The type of radiation can thus be controlled by tailoring the laser parameters.

High-order harmonic generation in liquids in bicircularly polarized laser fields

It is a nonlinear and nonperturbative optical phenomenon that high-order harmonic generation (HHG) can be produced by the interaction of intense laser pulses with liquid targets. The theoretical studies on HHG in liquids based on full dimensional simulations meet the difficulty of very low computational efficiency. Here, we develop an efficient numerical method based on the statistical mechanics in two-dimensional space, which reproduces the experimental HHG measurements very well. We also study the HHG in bicircularly polarized $1\ensuremath{\omega}$ $+$ $3\ensuremath{\omega}$ laser fields with the same field strength. It is found that near-circularly-polarized harmonics with different ellipticities can be generated in the counterrotating driving lasers. The cutoff energy of HHG in counter- and corotating driving lasers demonstrates a similar dependence of laser field strength and wavelength as that in the case of a linearly polarized driving laser field. This work paves the way for controlling the ultrafast electron dynamics in liquids by manipulating the laser fields.

Isolated attosecond pulse generation from the interaction of intense laser pulse with solid density plasma

This article gives an overview on recent progress in the generation of isolated attosecond pulse and isolated half-cycle attosecond pulse. As an isolated attosecond pulse is preferred in the pump-probe experiments for the dynamics of electrons in atom, molecule, or solid, we focus on the isolated attosecond pulses generation from the intense laser pulses interaction with solid density plasma, which have higher intensity and narrower pulse width than that generated in the interaction of laser pulse with gas target. We have firstly discussed the physical mechanism of isolated attosecond pulse generation, such as polarization gating, two-color laser pulses, attosecond light houses, and capacitor target mechanism. In the polarization gating mechanism, we have discussed the physical mechanism that the higher-order harmonic efficiency decreases with the increase of ellipticity. Both the coherent synchrotron radiation mechanism and the relativistic oscillation mechanism can control the intensity of high-order harmonic generation by controlling ellipticity of the incident laser pulse. We also discussed other mechanism to enhance the isolated attosecond pulse bursts in detail. Secondly, we focus on the isolated half-cycle attosecond pulses, which can also be generated from the intense laser pulses interaction with solid density plasma by double foil target mechanism, gas-foil target mechanism, cascaded generation mechanism, microstructured target mechanism, and three-color laser pulse mechanism. The half-cycle attosecond pulses can be useful for probing ultrafast electron dynamics in matter via asymmetric manipulation. Accordingly we discussed the physcial mechanism, experimental feasibility, calibration measurement, and application prospect of half-cycle attosecond pulse in this article. The above mechanism can directly generate ultra-intense isolated attosecond pulses in the transmission direction without requiring extra filters and gating techniques. The dense electron sheet is crucial for the generation of intense attosecond pulses in different mechanisms, such as coherent wake emission (CWE), relativistic oscillating mirror (ROM) and coherent synchrotron emission (CSE). In this article, all the mechanism for half-cycle attosecond pulses generation can ensure only one electron sheet contributing to the transmitted radiation. We discuss the theoretical model of nanobunching of the electron sheet, which shows that the relativistic oscillation is crucial for the formation of electron sheet.

Enhanced betatron x-ray emission in a laser wakefield accelerator and wiggler due to collective oscillations of electrons

We report x-ray emission caused by betatron motion of electrons in a laser wakefield accelerator driven by high intensity ($\ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$) laser pulse interaction with a 4-mm long helium gas-jet and study the role of collective oscillation of electrons as well as plasma density. The collective oscillations of electrons, inferred from the observed wavy pattern in the electron beam spectrum (up to 300 MeV) led to enhance peak x-ray flux which was found to be further enhanced at higher plasma densities. A similar correlation between the enhancement in x-ray emission and collective oscillation was also observed in nitrogen gas target. Possible physical pictures for the above observations are also suggested and discussed. For the helium gas jet target, the typically observed x-ray source brightness is $\ensuremath{\ge}1\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }\mathrm{photons}/\mathrm{s}\text{ }{\mathrm{mm}}^{2}\text{ }{\mathrm{mrad}}^{2}$ in 0.1% BW, with a critical energy of $35\ifmmode\pm\else\textpm\fi{}5\text{ }\text{ }\mathrm{keV}$. We have also demonstrated the application of the betatron x-ray source in high-resolution imaging.

Electron acceleration by relativistic pondermotive force in the interaction of intense laser pulse with an axially inhomogeneous underdense plasma

In this paper, electron acceleration by relativistic pondermotive force has been studied in the interaction of intense laser pulse with an axially inhomogeneous underdense plasma. The results show that the relativistic ponderomotive nonlinearity causes obvious beam self-focusing and a highly energetic electron can be achieved in the plasma, moreover, the high-energy electron would be automatically ejected by the ponderomotive force without adding any additional extractor. In addition, it is found that the real part and imaginary part of Lorentz factor can directly affect the amplitude and change the trend of electron acceleration, and electrons acceleration can be strengthened when we can elect properly the laser intensity with higher momentum and smaller beam width, but nonuniformity of plasmas can slightly decrease the electron acceleration. The results can provide useful physical support for novel design of table accelerator and the optimized parameters of electron acceleration in the plasma.

The transition from short- to long-timescale pre-pulses: Laser-pulse impact on tin microdroplets

We experimentally study the interaction of intense laser pulses with metallic microdroplets and the resulting deformation. Two main droplet deformation regimes have previously been established: that of sheet-type expansion after impact of “long” (typically >10 ns) pulses governed by incompressible flow and that of spherical expansion by internal cavitation after impact of “short” (typically <100 ps) pulses governed by shock waves, i.e., strongly compressible flow. In this work, we study the transition between these regimes by scanning pulse durations from 0.5 to 7.5 ns, where the boundaries of this range correspond to the limiting cases for the employed droplet diameter of 45 μm. We qualitatively describe the observed deformation types and find scaling laws for the propulsion, expansion, and spall-debris velocities as a function of pulse duration and energy. We identify the ratio of the pulse duration to the acoustic timescale of the droplet as the critical parameter determining the type of deformation. Additionally, we study the influence of fast rise times by comparing square- and Gaussian-shaped laser pulses. These findings extend our understanding of laser–droplet interaction and enlarge the spectrum of controllable target shapes that can be made available for future tin-droplet-based extreme ultraviolet sources.

Characterization of Laser-Induced Ionization Dynamics in Solid Dielectrics

The formation of an electron-hole plasma during the interaction of intense femtosecond laser pulses with transparent solids lies at the heart of femtosecond laser processing. Advanced micro- and nanomachining applications require improved control over the excitation characteristics. Here, we relate the emission of low-order harmonics to the strong laser-field-induced plasma formation. Together with a measurement of the total plasma density we identify the contribution of two competing ionization mechanisms - strong-field and electron-impact ionization.

Absorption of relativistic multi-picosecond laser pulses in wire arrays

We study the interaction of intense multi-picosecond laser pulses with arrays of carbon wires attached to solid substrates. We find that laser absorption in wire arrays resembles that in flat targets with very large uniform plasma density gradients. Performing two-dimensional particle-in-cell simulations, we optimize target parameters like wire thickness and distance for energy absorption of a 2 ps laser pulse with a large focal spot; this has implications for x-ray and charged particle source development.

Revisiting neutron yield in table-top nuclear fusion driven by an intense femtosecond laser pulse interaction with the gas clusters

With the development of femtosecond (fs) laser technology, an fs laser pulse with 10s of Joule, even 100s of Joule energy is available and the focused laser intensity can be expected to induce the pure Coulomb explosion of the cluster with a much larger average radius than before. Meanwhile, the production of gas cluster with an average radius of upto 10s of nanometer has been possible. In this case, it is necessary to reinvestigate the feasibility of 109 n/shot neutron yield for the practical application in the intense fs laser-driven nuclear fusion. In this work, the neutron yield from the explosions of the D2 clusters of 6–20 nm average radius at the 0.5–100 J pulse energy and the CD4 clusters was investigated theoretically. It is found that the optimum neutron yield of 109 n/shot can be obtained at the laser energy and the cluster radius currently available. However, a clustered-gas jet with a large cross-section is demanded to match the proper plasma diameter.

Stochastic heating of electrons due to Raman backscatter radiations in interaction of intense laser pulse with nitrogen atoms

In this paper, simulation study of electron stochastic heating arising from the Raman backscatter radiations during the interaction of the laser pulse with the nitrogen atoms is presented by use of a massively parallel particle-in-cell code. For this purpose, the self-consistent evolutions of the laser pulse via the time–space Fourier transforms of transvers vector potential are investigated at the different times of propagation. It is shown that since the ionization has effect on the emission of the Raman backscattered radiation; it noticeably contributes on the stochastic heating threshold of the electrons. According to our results, it has been found that, when there is the long rise time laser pulse (here 100 fs), the Raman backscattered radiations are seeded by a strong initial noise at the earlier times. Therefore, by considering the ionization, the necessary condition for chaos threshold is met sooner, which, in turn, causes the electron stochastic heating start quickly compared to the case the laser pulse is propagated in the pre-plasma. As a result, in agreement with chaotic nature of the motion, the electrons gain more energy through the stochastic mechanism in the field-ionized plasma.

Towards optimization of femtosecond laser pulse nanostructuring of targets for high-intensity laser experiments in vacuum

The interaction of intense femtosecond laser pulses with solid targets is a topic that has attracted a large amount of interest in science and applications. For many of the related experiments a large energy deposition or absorption as well as an efficient coupling to extreme ultraviolet (XUV), X-ray photon generation, and/or high energy particles is important. Here, much progress has been made in laser development and in experimental schemes, etc. However, regarding the improvement of the target itself, namely its geometry and surface, only limited improvements have been reported. The present paper investigates the formation of laser-induced periodic surface structures (LIPSS or ripples) on polished thick copper targets by femtosecond Ti:sapphire laser pulses. In particular, the dependence of the ripple period and ripple height has been investigated for different fluences and as a function of the number of laser shots on the same surface position. The experimental results and the formation of ripple mechanisms on metal surfaces in vacuum by femtosecond laser pulses have been analysed and the parameters of the experimentally observed “gratings” interpreted on base of theoretical models. The results have been specifically related to improve high-intensity femtosecond-laser matter interaction experiments with the goal of an enhanced particle emission (photons and high energy electrons and protons, respectively). In those experiments the presently investigated nanostructures could be generated easily in situ by multiple pre-pulses irradiated prior to a subsequent much more intense main laser pulse.

Hermite-cosh-Gaussian laser-induced third harmonic generation in plasma

Present work focuses on Hermite-cosh-Gaussian (HchG) laser-induced third harmonic generation (THG) in plasma on account of self-focusing. HchG laser beam gets self-focused due to ponderomotive force while propagating in plasma. Interaction of intense laser pulse results ponderomotive force on electrons and induce density perturbation that produces density oscillations at second harmonic frequency. Induced density perturbation beats with quiver velocity of electrons at laser frequency to produce a third harmonic nonlinear current. Application of wiggler magnetic field satisfies the phase matching condition which results resonant THG. Significant enhancement in the efficiency of THG is observed by using HchG laser profile for mode index m = 2. Small variation in decentered parameter also affects the THG efficiency which shows the sensitivity of decentered parameter.

Simulation of the interaction of intense ultrashort X-ray laser pulses with micro-sized Al targets

We study the interaction of extremely short and high-intensity X-ray pulses with a 1.0μm thick Al foil. Four pulse lengths – 100 fs, 200 fs, 300 fs, and 400 fs – are considered. The photon energy is 1830 eV and the pulse intensity is 1017W/cm2. The interaction dynamics are calculated via a radiation hydrodynamic code. The X-ray laser pulse heats the target isochorically. It generates a homogeneous hot dense matter; electrons are hotter than ions. The simulation of the interaction of pump and probe pulses with a delay time in the fs scale provides that the probe pulse heats the target significantly. A Monte-Carlo method is used to provide a microscopic description; the electron distribution function shows a two-temperature system. The electron distribution has spikes at the energy difference between the k-edges of Al ions and the energy of incident photons. The energies of these spikes depend on the considered ionization depression model. The Chihara formula and the non-equilibrium random phase approximation are utilized to calculate the X-ray Thomson scattering spectrum (XRTS). For collective scattering, the plasmon peaks are a function of the pulse lengths and the electron distribution function. Therefore, when XRTS is fitted to a measured spectrum may give the target density, the target temperature, and the microscopic electron distribution function.

Influence of pressure on spectral broadening of femtosecond laser pulses in air

Spectral broadening is an important nonlinear effect during the interaction of intense femtosecond laser pulses with air. In this paper, we experimentally study the dependence of spectral broadening on pressure and pulse energy. It is found that increasing both pressure and pulse energy can enhance the spectral intensity, while only increasing pressure leads to obvious blue shift of spectra, and the pulse energy has little effect on it. To get a better insight of the mechanism of spectral broadening, the numerical simulation relating the instantaneous frequency to the time dependent pulse intensity and time dependent plasma density in air is carried out. The results indicate that the plasma generation induced self-phase modulation which is related to the pressure plays an important role in blue shift of spectrum. Besides the transmission of the laser pulse is measured and decreases with pressure. It proves that the energy transfer of the laser pulse is promoted by pressure. This study will be helpful to understand a deeper physical mechanism of femtosecond filament induced supercontinnum generation in air.