High-intensity Laser Pulses Research Articles

Using Relativistic Self-Trapping Regime of a High-Intensity Laser Pulse for High-Energy Electron Radiotherapy

—Full-3D particle-in-cell Monte Carlo simulation of a new scheme of electron radiotherapy based on electron acceleration by high-power femtosecond laser pulse propagating in plasma of sub-critical density in the relativistic self-trapping regime (V. Yu. Bychenkov et al., Plasma Phys. Control. Fusion 61, 124004 (2019)) was carried out. Based on the results of simulation of distribution of energy deposited by electron bunches accelerated in such high-efficiency regime, it is demonstrated that a laser facility of gtrsim {kern 1pt} 100 TW class is capable of providing therapy of deep soft-tissue lesions in soft biotissue and this approach has a number of advantages relative to traditional methods of beam therapy.

Self-channeling of spatially modulated femtosecond laser beams in the post-filamentation region

The propagation of high-intensity femtosecond laser pulses in air under conditions of superposed spatial phase modulation is considered theoretically. The numerical simulations are carried out on the basis of the reduced form of a nonlinear Schrödinger equation for a time-averaged electric field envelope. Initial spatial modulations are applied to pulse wavefront profiling by a staggered ( T E M 22 ) phase plate, which is simulated numerically. The dynamics of laser pulse self-focusing, filamentation, and post-filamentation self-channeling after the phase plates with variable phase jumps is studied. We show that, with specific phase modulations, the pulse filamentation region in air can be markedly shifted further and elongated compared with a nonmodulated pulse. Moreover, during the post-filamentation propagation of spatially structured radiation, the highly localized light channels are formed, possessing enhanced intensity and reduced angular divergence, which enables post-filamentation pulse self-channeling on the distance multiple exceeding the Rayleigh range.

Achieving pair creation via linear and nonlinear Breit–Wheeler processes in dense plasmas irradiated by high-intensity laser pulses

It has been recently shown that over 109 electron–positron pairs can be produced from light alone at an experimentally accessible laser intensity of 5×1022W/cm2 by irradiating a target with a pre-formed channel by two counter-propagating laser pulses. Although targets of variable length and channel density have been successfully fabricated and used in recent experiments involving high-intensity lasers, the impact of these parameters on the pair yield by different pair creation processes is yet to be understood. In this paper, we explore, using two-dimensional particle-in-cell simulations, the impact of the channel density and length on pair production by the linear Breit–Wheeler process, nonlinear Breit–Wheeler process, and Bethe–Heitler process at fixed laser intensity. We find that these parameters can be successfully used to increase the linear Breit–Wheeler pair yield. More importantly, the relative contribution of each process can be adjusted by varying the same parameters. We show that this approach allows us to completely eliminate the yield from the nonlinear Breit–Wheeler process while maintaining a significant yield from the linear Breit–Wheeler process. The Bethe–Heitler process plays a secondary role in the considered system, so the majority of the positrons inside the channel are produced from light alone. Our results indicate that a structured target irradiated by two laser beams has the potential to be a versatile platform for future experimental studies of the Breit–Wheeler pair production processes, with the target parameters serving as control knobs.

Laser-induced breakdown spectroscopy signal enhancement effect for argon caused by the presence of gold nanoparticles

The effect of the presence of nanoparticles (NPs) on the laser induced breakdown spectroscopy (LIBS) signal of argon gas was studied experimentally. 10–20 nm diameter gold NPs, produced by a spark discharge nanoparticle generator, were suspended in argon gas. The effect of particle size, number concentration and mass concentration, as well as laser pulse energy on the LIBS argon signal was systematically investigated. It was found that the breakdown threshold of the gas decreases considerably, facilitating the detection of Ar emission at such laser fluences, which do not allow plasma formation without the presence of the NPs. Our observations persist even at aerosol mass concentrations that are too low to allow the direct detection of nanoparticles. The effect, which is attributed to electron thermo- and field emission induced by the high intensity laser pulse, shows an asymptotically increasing magnitude with the aerosol mass concentration. The signal enhancement was found to be 102–104 and the effect is suggested to be useful in trace gas analysis or for the indirect detection of NPs. The achievable indirect aerosol mass concentration detection limit was estimated to be in the parts per trillion regime (as low as 50 ng·m−3), which is comparable to the best literature values reported for direct analysis.

Comparative Additional Factor for Diffraction Loss On (TEM01) Mode from That of (TEM00) Mode

Comparative Additional Factor for Diffraction Loss On (TEM01) Mode from That of (TEM00) Mode

Time-of-flight methodologies with large-area diamond detectors for the effectively characterization of tens MeV protons

A novel detector based on a polycrystalline diamond sensor is here employed in an advanced time-of-flight scheme for the characterization of energetic ions accelerated during laser-matter interactions. The optimization of the detector and of the advanced TOF methodology allow to obtain signals characterized by high signal-to-noise ratio and high dynamic range even in the most challenging experimental environments, where the interaction of high-intensity laser pulses with matter leads to effective ion acceleration, but also to the generation of strong Electromagnetic Pulses (EMPs) with intensities up to the MV/m order. These are known to be a serious threat for the fielded diagnostic systems. In this paper we report on the measurement performed with the PW-class laser system Vega 3 at CLPU (∼30 J energy, ∼1021 W/cm2 intensity, ∼30 fs pulses) irradiating solid targets, where both tens of MeV ions and intense EMP fields were generated. The data were analyzed to retrieve a calibrated proton spectrum and in particular we focus on the analysis of the most energetic portion (E > 5.8 MeV) of the spectrum showing a procedure to deal with the intrinsic lower sensitivity of the detector in the mentioned spectral-range.

Multiscale study of high energy attosecond pulse interaction with matter and application to proton\u2013Boron fusion

For several decades, the interest of the scientific community in aneutronic fusion reactions such as proton–Boron fusion has grown because of potential applications in different fields. Recently, many scientific teams in the world have worked experimentally on the possibility to trigger proton–Boron fusion using intense lasers demonstrating an important renewal of interest of this field. It is now possible to generate ultra-short high intensity laser pulses at high repetition rate. These pulses also have unique properties that can be leveraged to produce proton–Boron fusion reactions. In this article, we investigate the interaction of a high energy attosecond pulse with a solid proton–Boron target and the associated ion acceleration supported by numerical simulations. We demonstrate the efficiency of single-cycle attosecond pulses in comparison to multi-cycle attosecond pulses in ion acceleration and magnetic field generation. Using these results we also propose a path to proton–Boron fusion using high energy attosecond pulses.

Multiphoton Phosphorescence of Simple Ketones by Visible-light Excitation and Its Consideration for Active Sensing in Space

Acetone and butanone were seen to emit blue light around 450 nm when excited in the green by a high intensity pulsed laser. The pathway of this anti-Stokes emission is believed to be multiphoton absorption followed by phosphorescence, with emission being observed in the samples at cryogenic temperatures below their melting point and not seen from either ketone in their cold liquid state. Given the widespread nature of these simple ketones in off-world bodies and their potential importance as an organic resource for Space Resource Utilization, signals which enable the identification and tracing of these materials are of use in applications from remote sensing and mapping to monitoring during extraction processes. While the excitation process has a low efficiency, the ability to use visible light for sensing of these targets has advantages over UV sources, such as the wider availability of high-powered lasers which could be utilized.

Subcycle terahertz field waveforms clocked by attosecond high-harmonic pulses from relativistic laser plasmas

A high-intensity ultrashort laser pulse interacting with a thin plasma target is shown to couple to plasma electrons, driving electron oscillations within the plasma and making these electrons bounce back and forth between plasma boundaries. Each time these recirculating electrons traverse the plasma boundary, they emit bright subcycle terahertz (THz) field waveforms via laser-driven coherent transition radiation. As a concurrent process, laser-driven electrons near the front surface of the plasma target are accelerated to relativistic velocities to emit high-order harmonics (HHs), giving rise to attosecond pulses of vacuum-ultraviolet radiation. These attosecond pulses are shown to provide a high-precision clock for subcycle THz field waveforms. We demonstrate that the delay time between HH pulses and THz waveforms can be tuned with an attosecond precision by varying the thickness of the plasma target, thus opening an avenue toward HH-pump–THz-probe studies of ultrafast processes on the attosecond time scale with table-top laser sources.

Weibel instability induced by kinetic stimulated Raman scattering in unmagnetized and magnetized plasmas

The kinetic stimulated Raman scattering (SRS) is found to result in significant Weibel-generated magnetic fields via 2D particle-in-cell simulations. During the high-intensity laser pulse, the daughter electron plasma waves of SRS heat the electrons effectively and lead to anisotropy in the velocity space. This anisotropy results in the development of a quasi-static magnetic field near the laser speckle, and the growth rate has been discussed. The results show that the kinetic SRS can lead to an averaged magnetic field of more than 10 T, which can be an important magnetic field source in laser-plasma experiments. Besides, the energy of the Weibel-field undergoes an oscillatory rise with the SRS bursts and can be stable after cutting off the laser. Moreover, in the magnetized plasmas, the application of a longitudinal magnetic field enhances the SRS, but interestingly, it significantly reduces the growth rate of Weibel instability. Simulation results also indicate that a small transverse magnetic field can evidently change the motion of the hot electrons, which dramatically destroys the symmetry of the SRS and the Weibel-generated magnetic fields.

Investigation of electrical conductivity effects on cluster characteristics of Ar and Xe

The phenomenon of cluster interaction with high-intensity laser pulses is of great scientific importance as well as potential applications. To explain such phenomena, in rare gasses, several models have been proposed, among which the nanoplasma model is the most successful one since it considers interaction that take into account the processes of ionization, heating and explosion simultaneously. However, the reported results need to be completed, enriched and quantified either experimentally or theoretically. In this context, we investigate the effects of femtosecond laser-cluster interactions in argon and xenon noble gasses on several parameters and their interdependences: electrical conductivity, σ, Debye length,λD2, coupling parameter,Γc, loss tangent, tanδ. To do so, we carry out numerical simulations based on the characteristics and assumptions of the nanoplasma model. Several interesting results were deduced for both Ar and Xe, such as: a linear increase of tanδ with ImgλD2 for all investigated values of σ, an increase in σ with normalized Debye length as well as normalized 1/ΓC (with a sharper initial increase) and the imaginary part of 1/ΓC increases linearly with tanδ. It should be noted that all these variations were quantified and new semi empirical formula were deduced. It was also put into evidence that the same mechanism is responsible for the variations of both coupling parameter and the Debye length.

Intensity scaling limitations of laser-driven proton acceleration in the TNSA-regime

We report on experimental results on laser-driven proton acceleration using high-intensity laser pulses. We present power law scalings of the maximum proton energy with laser pulse energy and show that the scaling exponent $\ensuremath{\xi}$ strongly depends on the scale length of the preplasma, which is affected by the temporal intensity contrast. At lower laser intensities, a shortening of the scale length leads to a transition from a square root toward a linear scaling. Above a certain threshold, however, a significant deviation from this scaling is observed. Two-dimensional particle-in-cell simulations show that, in this case, the electric field accelerating the ions is generated earlier and has a higher amplitude. However, since the acceleration process starts earlier as well, the fastest protons outrun the region of highest field strength, ultimately rendering the acceleration less effective. Our investigations thus point to a principle limitation of the proton energy in the target normal sheath acceleration regime, which would explain why a significant increase of the maximum proton energy above the limit of $100\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ has not yet been achieved.

Effect of pulsed electromagnetic field versus pulsed high intensity laser in the treatment of men with osteopenia or osteoporosis: a randomized controlled trial

Background: Osteoporosis has been related to a negative impact on several aspects of patient health, including physical, mental, and emotional well-being. The objective of this study was to examine the effects of pulsed electromagnetic fields (PEMF) and pulsed Nd-YAG laser therapy (HILT) on men with osteopenia or osteoporosis. Methods: Ninety-five men with osteopenia or osteoporosis (mean age, 52 years; mean height, 176 cm; mean weight, 83 kg; mean body-mass index (BMI), 26.86 kg/m2) took part in the study, and they were randomly assigned to one of three groups: Group 1 received PEMF and exercise program (PEMF +EX), Group 2 received HILT and exercise program (HILT+EX), and Group 3 received exercise program only (EX). PEMF was applied three times per week for 12 weeks using a full-body mat, while HILT was applied to the lower back and hip regions with a total dose of energy of 3000 J delivered in two treatment stages. Flexibility, aerobic exercise, strength, weight-bearing, and balance exercises are included in exercise program, which is followed by whole-body vibration training. Bone mineral density (BMD) of the total hip and lumbar spine, bone markers, health-related quality of life (HRQoL), and fall risk are all outcome measures. Results: There were no significant differences in the parameters between the groups at the baseline (P > 0.05). Patients in all groups, however, showed significant improvements in all measured parameters following treatment (P< 0.05), with Group 1 and Group 2 showing much greater improvements than Group 3. Conclusion: After 12-weeks of treatment, PEMF combined with exercise is more effective than HILT combined with exercise or exercise alone in increasing BMD and promoting bone formation, suppressing bone-resorption markers, and improving quality of life and fall risk, with the effects lasting up to six months. This study was registered in the ClinicalTrial.gov PRS (NCT05029440, 26/08/2021).

Interstrand Crosslinking Involving Guanine: A New Major UVC Laser-Induced Biphotonic Oxidatively Generated DNA Damage.

Several classes of oxidatively generated DNA damage including oxidized purine and pyrimidine bases, interstrand base crosslinks and DNA-protein crosslinks have been previously shown to be generated in both isolated DNA and cellular DNA upon exposure to either 266-nm laser irradiation or one-electron oxidants. In this study, we provide evidence that biphotonic ionization of guanine bases by UVC laser irradiation of double-stranded deoxyoligonucleotides in aerated aqueous solutions induces the formation of interstrand crosslinks (ICLs). This is supported by various experiments including sequencing gel analyses of formed photoproducts and effects of UVC laser intensity on their formation. This constitutes a novel example of the diversity of reactions of guanine radical cation that can be generated by various one-electron oxidants including UVC laser biphotonic ionization, direct effect of ionization radiation and type I photosensitizers. However, the exact structure of the interstrand base adducts that is a challenging analytical issue remains to be further established. Examples of relevant biochemical/structural applications of biphotonic induction of ICLs in DNA samples by high-intensity UVC laser pulses are provided.

Спектрально-угловые характеристики излучения заряженной частицы в поле Редмонда

Based on the solution of the equation of motion of a charge in an electromagnetic field, the classical theory of radiation of a relativistic charged particle linearly accelerated by a high-intensity laser pulse in the presence of a static component of the magnetic field is constructed. Solutions obtained by Kopytov G.F. and Pogorelov A.V., were used to study the spectral-angular characteristics of the radiation of a charged particle in a combination of the field of a plane monochromatic electromagnetic wave and a constant magnetic field, the so-called Redmond field. According to the calculated formulas for the radiation intensity of particles in the Redmond field, graphs of the dependence on the magnitude of the magnetic field, phase and phase-angular distributions are plotted. The Fourier transform of the intensity of the electric field of the radiation and the spectral density of the radiation of the particle in the case of linear polarization of the wave is obtained.

Spectral-angular characteristics of the radiation of a charged particle in the Redmond field

Based on the solution of the equation of motion of a charge in an electromagnetic field, the classical theory of radiation of a relativistic charged particle linearly accelerated by a high-intensity laser pulse in the presence of a static component of the magnetic field is constructed. Solutions obtained by Kopytov G.F. and Pogorelov A.V., were used to study the spectral-angular characteristics of the radiation of a charged particle in a combination of the field of a plane monochromatic electromagnetic wave and a constant magnetic field, the so-called Redmond field. According to the calculated formulas for the radiation intensity of particles in the Redmond field, graphs of the dependence on the magnitude of the magnetic field, phase and phase-angular distributions are plotted. The Fourier transform of the intensity of the electric field of the radiation and the spectral density of the radiation of the particle in the case of linear polarization of the wave is obtained. Keywords: Redmond field, spectral-angular characteristics, charged particle, Lawson-Woodward theorem, superpower laser radiation.

Isolated attosecond pulse generation from helium atom irradiated by a three-color laser pulse

Isolated attosecond pulses enables the studying and controlling of ultrafast electron processes in atoms and molecules. High-order harmonic generation (HHG) is the most promising way to generate such pulses, benefiting from the broad plateau structure of the typical HHG spectrum. We theoretically investigate high-order harmonic and attosecond pulse generation from helium atom in a three-color laser field, which is synthesized by 16 fs/1600 nm, 15 fs/1100 nm and 5 fs/800 nm pulse laser. Compared with harmonic spectrum generated by a two-color laser field synthesized by 16 fs/1600 nm and 15 fs/1100 nm, the harmonic spectrum generated from the synthesized three-color field exhibits high conversion efficiency and broadband supercontinuum characteristics. The continuous spectrum range covers from 230th to 690th harmonics, and the generation of 128 attosecond isolated short pulses with higher intensity is realized after Fourier transform. This result is attributable to the fact that the synthesized three-color electric field exhibits high-intensity and few-cycle mid-infrared femtosecond pulse laser characteristics, which can effectively control atomic ionization and recombination occurring within an effective optical period of the mid-infrared femtosecond pulse. This scheme solves the problems faced by the current femtosecond pulse laser technology, i.e. the few-cycle mid-infrared femtosecond pulse laser cannot have both carrier envelope phase stability and high power output.

Intense ү-Ray Bursts following the Interaction of Laser Pulse with Steep Density Gradients

We investigate the production of intense ү-rays following the interaction of ultraintense laser pulse with a hybrid combination of under-dense plasma associated with a thin foil of fully ionized Al or Cu or Au at the rear side. Relativistic electrons are accelerated following the interaction of high intensity laser pulses with an under-dense plasma. These electrons are then stopped by the thin foils attached to the rear side of the under-dense plasma. This results in the production of intense-ray bursts. So, the enhancement of photon generation is due to the under-dense plasma electrons interacting with different over-dense plasma. Using open-source PIC code EPOCH, we study the effect of different electron densities in the under-plasma on photon emission. Photon emission enhancement is observed by increasing the target Z in the hybrid structure. Hybrid structure can enhance photon emission; it can increase the photon energy and yield and improve photon beam divergence. Simulations were also performed to find the optimal under-dense plasma density for ү-ray production.

Self-compression of a high-intensity laser pulse in a double-ionizing gas

The self-compression and spatiotemporal evolution of a Gaussian laser pulse propagating in a double-ionized helium gas are investigated. The numerical model is formulated by solving the nonlinear Schrödinger equation using the paraxial like approach. The beam width parameter and pulse width parameter are estimated to investigate the laser pulse advancement in a tunnel ionizing gas. Transverse focusing and longitudinal compression are examined by characterizing the beam spot size in space and time, incorporating the gas ionization processes, relativistic mass variation, and ponderomotive effects. The results show that the inclusion of laser-induced double ionization of helium gas modifies the plasma density, which significantly affects the laser pulse evolution. For intense laser pulse, relativistic-ponderomotive nonlinearity enhances the pulse compression and consequently the self-focusing of the laser pulse. The compression mechanism and the localization of the pulse intensity both are boosted by the modified electron density via a dielectric function. At a helium gas pressure of 1.4 bar, we observed that 100 fs long laser pulse with intensity I0=8.5×1016 W/cm2 is compressed to 20 fs and the initial laser spot size 10 μm focused to 2 μm. These results promise to be a method for the generation of table-top light sources for ultrafast high-field physics and advanced optics.

Kilo-Tesla axial magnetic field generation with high intensity spin and orbital angular momentum beams

Absorption of angular momentum from a high intensity laser pulse can lead to the generation of strong axial magnetic fields in plasma. The effect, known as the inverse Faraday effect, can generate kilo-Tesla strength, multipicosecond, axial magnetic fields extending over hundreds of microns in underdense plasma. In this paper we explore the effect with ultrahigh intensity circularly polarized Gaussian beams and linearly polarized orbital angular momentum beams comparing analytic expressions with three-dimensional particle-in-cell simulations. We develop a model for the transverse magnetic field profiles, introduce a model for the temporal decay, and show that while the magnetic field strength is independent of plasma density, it has a strong dependence on the laser beam waist.