Intense Short Pulse Research Articles

Safety and quality of life assessment at 6 months follow-up of the valvosoft pivotal study

Abstract Background Calcific Aortic stenosis (CAS) is currently the most common heart valve disease. Patients suffering from severe CAS are treated with invasive surgeries based on valve replacement. Symptoms heavily impact quality of life, including chest pain, shortness of breath, dizziness, fatigue, and major risks as heart failure or sudden death, and daily activities might also be strongly impacted. Purpose A prospective, multi-centre, single-arm, pivotal study (NCT05235568) was initiated in 2021 to treat severe CAS patients with Valvosoft, a medical device based on Non-Invasive Ultrasound Therapy (NIUT) intended to treat CAS in patients not eligible for immediate aortic valve replacement (SAVR/TAVR) or refusing such a treatment, to confirm safety and performance at 1-, 3-, 6- and 12 months. We present here the safety and quality of life results at 6M follow-up. Methods Valvosoft NIUT procedure is based on a trans-thoracic delivery of focused, high intensity short therapeutic ultrasound pulses, to precisely generate a cavitation bubble cloud on the aortic valve. Echocardiographic imaging enables to monitor the valve in real-time while cavitation causes both non-thermal tissue softening and calcification fractionation of the diseased valve. 60 planned subjects, suffering from severe calcific aortic stenosis, not recommended for aortic valve replacement or refusing such a procedure, were enrolled in 11 centres in Europe. Patients were awake or lightly sedated, NIUT was delivered during up to 70 minutes per patient per procedure. DSMB and CEC were installed to monitor safety, performance and effectiveness of Valvosoft device, and safety related to participation in the clinical investigation. Results Sixty high-risk patients advanced in age (85.2 ± 9.1) with multiple severe comorbidities were included. Primary safety endpoint (less than 25% MACE) was met at 30D (p=0.002). Furthermore patients experienced an overall quality of life improved. 6 minutes’ walk test increases from baseline towards 6 months with 10 %. At 6M follow-up, no stroke was reported, an average KCCQ score improvement of 17% was noticed, and NYHA class improved or stabilized for 78% of patients. The calcium score or volume on the aortic did not change pre- and post-procedure. Conclusion Valvosoft NIUT safety and quality of life improvement are proven at 6MFU, and the technology is presented as potentially disruptive, in the treatment of severe calcific aortic stenosis.

Optimization of laser-driven quantum beam generation and the applications with artificial intelligence

We have investigated space and astrophysical phenomena in nonrelativistic laboratory plasmas with long high-power lasers, such as collisionless shocks and magnetic reconnections, and have been exploring relativistic regimes with intense short pulse lasers, such as energetic ion acceleration using large-area suspended graphene. Increasing the intensity and repetition rate of the intense lasers, we have to handle large amounts of data from the experiments as well as the control parameters of laser beamlines. Artificial intelligence (AI) such as machine learning and neural networks may play essential roles in optimizing the laser and target conditions for efficient laser ion acceleration. Implementing AI into the laser system in mind, as the first step, we are introducing machine learning in ion etch pit analyses detected on plastic nuclear track detectors. Convolutional neural networks allow us to analyze big ion etch pit data with high precision and recall. We introduce one of the applications of laser-driven ion beams using AI to reconstruct vector electric and magnetic fields in laser-produced turbulent plasmas in three dimensions.

Raman time-delay in attosecond transient absorption of strong-field created krypton vacancy

Strong field ionization injects a transient vacancy in the atom which is entangled to the outgoing photoelectron. When the electron is finally detached, the ion is populated at different excited states with part of coherence information lost. The preserved coherence of matter after interacting with intense short pulses has important consequences on the subsequent nonequilibrium evolution and energy relaxation. Here we employ attosecond transient absorption spectroscopy to measure the time-delay of resonant transitions of krypton vacancy during their creation. We have observed that the absorptions by the two spin-orbit split states are modulated at different paces when varying the time-delay between the near-infrared pumping pulse and the attosecond probing pulse. It is shown that the coupling of the ions with the remaining field leads to a suppression of ionic coherence. Comparison between theory and experiments uncovers that coherent Raman coupling induces time-delay between the resonant absorptions, which provides insight into laser-ion interactions enriching attosecond chronoscopy.

Extraordinary transmission of intense short laser pulse through thin foil with near- and sub-wavelength slits

To supplement our earlier study [Lu et al., AIP Adv. 10, 015209 (2020)] on the propagation of intense short laser pulse through foils with multiple sub-wavelength sized slits, here, we consider the effects of the interaction parameters on the occurrence of extremums in the light transmission. Our results suggest that for periodic slit distribution, maximum and minimum transmissions occur for L ± d = κλ and L = κλ, respectively, where L and d are the period and width of the slits, respectively, λ is the laser wavelength, and κ is a positive integer or a rational number.

The femtosecond structure of extreme contrast, multi-terawatt second-harmonic laser pulses at 400 nm

Ultrahigh intensity contrast and short pulse laser–solid interactions offer an attractive platform for investigating high-energy-density matter, particularly in the context of structured and ultra-thin targets that form hot, dense plasma conditions. Harmonic generation can improve the contrast of laser pulses by several orders of magnitude. In this study, we present the characterization of extreme contrast, relativistic intensity second-harmonic pulses at 400 nm, using the self-diffraction frequency-resolved optical gating technique. The 400 nm pulses were generated at various input intensities using potassium dihydrogen phosphate and lithium triborate crystals. Our observations reveal the presence of spectral broadening, pulse compression, and complex structures at higher input intensities. We see that extreme contrast, few tens of femtosecond pulses can have multiple “prepulses” at the 100s femtosecond scale as large as ten percent of the peak value. These can preionize a solid significantly and may influence the interaction. Simulations based on nonlinear pulse propagation equations reinforce our findings.

Kinetic Interaction between an Electron Flow with a Wide Velocity Spread and a Short-Adjusted Slipping Wave Pulse at the Cherenkov Resonance

In this study, kinetic interaction at the Cherenkov resonance between an electromagnetic wave pulse and a flow of electrons possessing a wide velocity spread at the scale of the characteristic range of the resonant electron wave interaction is considered. Due to the absence of a distribution function slope in the range of velocities corresponding to the electron wave’s resonance, an electron’s flow is a nearly stable media from the point of view of its interaction with a long enough wave pulse. In this paper, we explain our findings on the process of electron interaction with potential relief where the wave pulse is so short that the characteristic scale of the wave amplitude’s inhomogeneity and the profile of the potential relief is comparable to the wavelength. We show that if an appropriate slippage between the phase and group velocities of the wave is provided, then the reflection process of particles from “fast” and “slow” close-to-resonance velocity fractions becomes non-symmetrical. This can provide a mechanism of amplification of short intensive wave pulses with electron flows with very large velocity spreads.

Nonlinear evolution of the Weibel instability with relativistic laser pulses

The Weibel instability is investigated using relativistic intense short laser pulses. A relativistic short laser pulse can generate a sub-relativistic high-density collisionless plasma. By irradiating double parallel planar targets with two relativistic laser pulses, sub-relativistic collisionless counterstreaming plasmas are created. Since the growth rate of the Weibel instability is proportional to the plasma density and velocity, the spatial and temporal scales of the Weibel instability can be much smaller than that from nanosecond large laser facilities. Recent theoretical and numerical studies have revealed that astrophysical collisionless shocks in sub-relativistic regimes in the absence and presence of an ambient magnetic field play essential roles in cosmic ray acceleration. With experimental verification in mind, we discuss the possible experimental models on the Weibel instability with intense short laser pulses. In order to show the experimental feasibility, we perform 2D particle-in-cell simulations in the absence of an external magnetic field as the first step and discuss the optimum conditions to realize the nonlinear evolutions of the Weibel instability in laboratories.

Manifestations of Rabi Dynamics in the Photoelectron Energy Spectra at Resonant Two-Photon Ionization of Atom by Intense Short Laser Pulses

We study the Rabi flopping of the population between the ground and excited 2p states of the hydrogen atom, induced by intense short laser pulses of different shapes and of carrier frequency ω=0.375 a.u. which resonantly couples the two states, and manifestations of this dynamics in the energy spectra of photoelectrons produced in the subsequent ionization of the atom from the excited state. It is found that, for Gaussian, half-Gaussian and rectangular pulses, characterized by the same pulse area, the final populations take the same values and the spectra consist of similar patterns having the same number of peaks and approximately the same separation between the prominent edge (Autler–Townes) peaks. The additional analysis in terms of dressed states showed that the mechanism of formation of multiple-peak structures during the photoionization process is the same regardless of the pulse shape. These facts disprove the hypothesis proposed in earlier studies with Gaussian pulse, that the multiple-peak pattern appears due to dynamic interference of the photoelectrons emitted with a time delay at the rising and falling sides of the pulse, since the hypothesis is not applicable to either a half-Gaussian pulse that has no rising part or a rectangular pulse whose intensity is constant.

Linear dual-comb interferometry at high power levels.

Detector non-linearity is an important factor limiting the maximal power and hence the signal-to-noise ratio (SNR) in dual-comb interferometry. To increase the SNR without overwhelming averaging time, photodetector non-linearity must be properly handled for high input power. Detectors exhibiting nonlinear behavior can produce linear dual-comb interferograms if the area of the detector's impulse response does not saturate and if the overlap between successive time-varying impulse responses is properly managed. Here, a high bandwidth non-amplified balanced photodetector is characterized in terms of its impulse response to high intensity short pulses to exemplify the conditions. With a 23.5 mW average power on each detector in a balanced pair, nonlinear spectral artifacts are at least 40 dB below the spectral baseline. Absorption lines of carbon dioxide are measured to reveal lines discrepancies smaller than 0.1% with HITRAN. A spectral shape independent formulation for the dual-comb figure of merit is proposed, reaching here 7.2 × 107 Hz1/2 limited by laser relative intensity noise, but corresponding to an ideal, shot-noise limited, figure of merit for an equivalent 0.85 mW average power per comb.

Laser pulse cutoff at nonlinear reflection due to Raman backscattering in plasma.

A method for generating subrelativistic laser pulses with a sharp leading edge is proposed, which is based on Raman backscattering of an intense short pump pulse by a counter-propagating long low-frequency pulse propagating in a thin plasma layer. A thin plasma layer serves both to attenuate parasitic effects and to effectively reflect the central part of the pump pulse when the field amplitude exceeds the threshold value. A prepulse with a lower field amplitude passes through the plasma almost without scattering. This method works for subrelativistic laser pulses with durations up to 100 fs. The contrast of the leading edge of the laser pulse is determined by the seed pulse amplitude.

Generation of single circularly polarized attosecond pulses from near-critical density plasma irradiated by a two-color co-rotating circularly polarized laser.

In this paper, a new method is proposed to efficiently generate a single intense attosecond pulse with circular polarization (CP) through the interaction of an intense driving laser with a near-critical density plasma target. The driving laser is composed of two co-rotating CP lasers with similar frequencies but different pulse widths. When the matching condition is satisfied, the combined field is modulated to a short intense pulse followed by a weak tail. The resulting laser falling edge becomes steeper than the initial sub-pulses, which induces a quick one-time oscillation of the target surface. Meanwhile, the tail guarantees the energy to be compressed simultaneously in both polarization directions to the same extent, so that a single CP attosecond pulse can be produced efficiently and robustly via our method, which has been confirmed through extensive numerical simulations. In addition, our method makes it possible to generate a single CP attosecond pulse even for multi-cycle pulses that are already available for existing laser systems. This provides a novel way to advance the investigation of chiral-sensitive light-matter interactions in attosecond scales.

Coulomb effects in the high-energy part of above-threshold-ionization spectra in intense bicircular laser fields

Coulomb effects in the high-energy part of photoelectron spectra produced through the above-threshold ionization of an atom subject to intense short laser pulses are analyzed. The analysis is carried out for linearly polarized and tailored bicircular laser pulses consisting of the fundamental and the second-harmonic components. We include the Coulomb effects in the analytic semiclassical description of the photoelectron rescattering plateau using the recently developed adiabatic approach [Phys. Rev. A 104, 033109 (2021)] and the expression for the Coulomb phase derived for description of the high harmonic generation [J. Phys. B: At., Mol. Opt. Phys. 51, 144006 (2018)]. Comparisons between predictions of the analytic approach and numerical solutions of the time-dependent Schr\"odinger equation are presented. They allow the identification of the contribution of the Coulomb interaction to photoelectron spectra for different laser pulse forms. We show that the Coulomb effects appear more pronounced for bicircular fields, where they demonstrate considerable sensitivity to the photoelectron emission angle. Instead, for linear polarization, the Coulomb effect in the high-energy plateau is generally insignificant.

Density-matrix approach for sequential dissociative double ionization of molecules

Intense femtosecond infrared (IR) laser pulses have been used in recent years to study the breakup dynamics of molecules. However, observables such as kinetic energy release and branching ratios of molecular fragments are often difficult to predict by theory, making information of the molecular dynamics difficult to retrieve. In this work, we develop a simple model for sequential double ionization of molecules based on a density-matrix approach. The model describes tunneling ionization of the neutral and the ion as well as laser couplings between the ionic states simultaneously. Population of different doubly charged states can be obtained at a low computational cost. We applied our model to ${\mathrm{N}}_{2}$ and obtained a good agreement on the kinetic energy release spectrum with a previous experiment. This theoretical development could open up the opportunities to use intense short IR laser pulses with coincidence measurement to probe molecular dynamics.

Efficient ion acceleration by multistaged intense short laser pulses

We present a computational study of laser-driven ion acceleration that optimizes a combination of target transparency and extended field acceleration at moderate relativistic intensity. Our scheme applies two sequential laser pulses irradiating a thin target foil along the same direction: The first pulse drives a rapid expansion of the target, while the second one drives a quasistatic electric field in the expanding target with increasing electron temperature. In our particle-in-cell simulations we observe proton peak energies and numbers enhanced by factors of up to 3 compared with regular target-normal sheath acceleration.Received 6 October 2020Accepted 4 May 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.L032003Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHigh-energy-density plasmasLaser driven ion accelerationAccelerators & BeamsPlasma PhysicsParticles & Fields

Shock Waves in Weakly Relativistic e-p-i Plasma: Application to Plasma Created by Ultraintense Short Pulse Laser

In this article, the role of the positrons shock waves generation in weakly relativistic laser-created plasma is investigated. The plasma considered is generated on the rear face of a target, irradiated by a high intensity short pulse laser, in the framework of target normal sheath acceleration (TNSA) mechanism. This plasma is composed of Boltzmann distributed positrons, hot and cold super-thermal electrons, and dynamic ions. Kinematic viscosity among the plasma constituents has been also considered. With the purpose of studying the behavior of nonlinear ion acoustic shock waves (IASHWs), the reductive perturbation method (RPM) has been employed and Korteweg-de Vries Burgers equation has been derived. It was observed that different plasma parameters (namely, electrons super-thermality, number of positrons, ion temperature, kinematic viscosity, etc.) have a real impact on the propagation of IASHWs. As electron–positron plasmas with ion possessing relativistic velocities are often detected in laboratory experiments, astrophysical, and space environments, the present work will help to explain the different types of collective processes and instabilities in regions where e-p-i plasmas can exist.

Experimental verification of TNSA protons and deuterons in the multi-picosecond moderate intensity regime

Ion acceleration from high intensity short pulse laser interactions is of great interest due to a number of applications, and there has been significant work carried out with laser energies up to a few 100 J with 10's of femtosecond to 1 ps pulse durations. Here, we report results from an experiment at the OMEGA EP laser, where laser energy and pulse length were varied from 100 to 1250 J and 0.7–30 ps, respectively, in the moderate (2×1017–2×1018 W/cm2) laser intensity regime. Ions and electrons were simultaneously measured from disk targets made of CH and CD by a Thomson parabola and a magnetic spectrometer, respectively. Measurements showed that the electron temperature, Te (MeV), has a dependence on the laser energy, EL (J), and pulse duration, τL (ps), and its empirical scaling was found to be 0.015×EL0.90τL−0.48. The maximum proton and deuteron energies are linearly dependent on the electron temperature, (5.60 ± 0.26)×Te and (3.17 ± 0.18)×Te, respectively. A significant increase in proton numbers with the laser energy was also observed. The increase in the maximum proton energy and proton count with higher energy longer duration pulses presented in this article shows that such laser conditions have a great advantage for applications, such as the proton radiograph, in the moderate laser intensity regime.

Two-dimensional parametric design of short pulse laser driven iron opacity experiments

High intensity short pulse lasers are commonly used to create high temperature and high density plasmas. These plasmas are used to study fundamental properties such as the equation of state and opacity. The targets often use small-diameter, thin buried layers of the materials of interest, surrounded by a tamper of low atomic number material such as plastic. Computational modeling is used to design and interpret experiments with short pulse lasers. Most of the modeling to date has assumed one-dimensional plane-parallel geometry. In this paper, the effects of radial gradients in the irradiation of thin planar targets are studied with one- and two-dimensional radiation/hydrodynamic simulations. It is found that the main effect of radial gradients is the averaging of plasma conditions and x-ray emission over the pattern of irradiation. Differences between one- and two-dimensional simulations arise because the plasma conditions and x-ray emission are, in general, nonlinear functions of the temperature of the plasma and thereby also nonlinear functions of the irradiation intensity. The differences increase with the ratio of the buried layer radius to the laser spot radius. The root mean square difference in the inferred iron L-shell opacity is less than 30% when the ratio is less than 1.0 and about 70% when the ratio is 1.5.

Ultrashort laser-driven dynamics of massless Dirac electrons generating valley polarization in graphene

We identify and describe how intense short light pulses couple to massless Dirac fermions in two-dimensional systems. The ensuing excitation dynamics exhibits unusual scaling with the wavelength of the light due the linear dispersion of the band structure and the fact that light coupling is efficient only close to the Dirac points. We exploit these features to achieve valley polarization of more than 70 % with simple pulse shapes. Quantitative results are given for pristine graphene.

High brilliance beam investigations at the universal linear accelerator

The more than 45-year-old GSI-UNILAC (universal linear accelerator) as well as the heavy ion synchrotron SIS18 will serve as a high-current heavy ion injector for the new Facility for Antiproton and Ion Research (FAIR) synchrotron SIS100. UNILAC will serve together with the SIS18 as FAIR injector for short intense pulse operation; the newly developed heavy ion linac Helmholtz linear accelerator shall deliver cw beams, still required for the comprehensive research program at GSI. In the context of an advanced machine investigation program in combination with the ongoing UNILAC upgrade program, a dedicated beam investigation campaign has been carried out in order to characterize front-to-end high-current medium and heavy ion beam behavior at GSI-UNILAC. A very high beam brilliance at the end of transfer line from UNILAC to SIS18 was achieved recently for medium heavy ion beams in a machine experiment campaign. This is an important step paving the way to fulfill the FAIR heavy ion high-intensity beam requirements. Results of high-current uranium beam measurements applying the novel technique of pulsed hydrogen gas stripping (at $1.4\text{ }\text{ }\mathrm{MeV}/\mathrm{u}$) will be presented as well.

A rate model approach for FEL pulse induced transmissions changes, saturable absorption, X-ray transparency and stimulated emission

As the use of free electron laser (FEL) sources increases, so do the findings mentioning non-linear phenomena occurring at these experiments, such as saturable absorption, induced transparency and scattering breakdowns. These are well known among the laser community, but are still rarely understood and expected among the X-ray community and to date lack tools and theories to accurately predict the respective experimental parameters and results. We present a simple theoretical framework to access short X-ray pulse induced light–matter interactions which occur at intense short X-ray pulses as available at FEL sources. Our approach allows to investigate effects such as saturable absorption, induced transparency and scattering suppression, stimulated emission, and transmission spectra, while including the density of state influence relevant to soft X-ray spectroscopy in, for example, transition metal complexes or functional materials. This computationally efficient rate model based approach is intuitively adaptable to most solid state sample systems in the soft X-ray spectrum with the potential to be extended for liquid and gas sample systems as well. The feasibility of the model to estimate the named effects and the influence of the density of state is demonstrated using the example of CoPd transition metal systems at the Co edge. We believe this work is an important contribution for the preparation, performance, and understanding of FEL based high intensity and short pulse experiments, especially on functional materials in the soft X-ray spectrum.