Optical Control of the Topology of Laser-Plasma Accelerators.

We propose a twisted plasma accelerator capable of generating relativistic electron vortex beams with helical current profiles. The angular momentum of these vortex bunches is quantized, dominates their transverse motion, and results in spiraling particle trajectories around the twisted wakefield. We focus on a laser wakefield acceleration scenario, driven by a laser beam with a helical spatiotemporal intensity profile, also known as a light spring. We find that these light springs can rotate as they excite the twisted plasma wakefield, providing a new mechanism to control the twisted wakefield phase velocity and enhance energy gain and trapping efficiency beyond planar wakefields.

Axion-Plasmon Polaritons in Strongly Magnetized Plasmas.

Axions are hypothetical particles related to the violation of the charge-parity symmetry within the strong sector of the standard model, being one of the most prone candidates for dark matter. Multiple attempts to prove their existence are currently performed in different physical systems. Here, we predict that axions may couple to the electrostatic (Langmuir) modes of a strongly magnetized plasma, and show that a new quasiparticle can be defined, the axion-plasmon polariton. The excitation of axions can be inferred from the pronounced modification of the dispersion relation of the Langmuir waves, a feature that we estimate to be accessible in state-of-the-art plasma-based experiments.

High Orbital Angular Momentum Harmonic Generation.

We identify and explore a high orbital angular momentum (OAM) harmonics generation and amplification mechanism that manipulates the OAM independently of any other laser property, by preserving the initial laser wavelength, through stimulated Raman backscattering in a plasma. The high OAM harmonics spectra can extend at least up to the limiting value imposed by the paraxial approximation. We show with theory and particle-in-cell simulations that the orders of the OAM harmonics can be tuned according to a selection rule that depends on the initial OAM of the interacting waves. We illustrate the high OAM harmonics generation in a plasma using several examples including the generation of prime OAM harmonics. The process can also be realized in any nonlinear optical Kerr media supporting three-wave interactions.

Bose-Einstein condensation of photons in microcavity plasmas.

Bose-Einstein condensation of a finite number of photons propagating inside a plasma-filled microcavity is investigated. The nonzero chemical potential is provided by the electrons, which induces a finite photon mass and allows condensation to occur. We derive an equation that models the evolution of the photon-mode occupancies, with Compton scattering taken into account as the mechanism of thermalization. The kinetic evolution of the photon spectrum is solved numerically, and we find evidence of condensation down to nanosecond timescales for typical microplasma conditions, n_{e}∼10^{14}-10^{15}cm^{-3}. The critical temperature scales almost linearly with the number of photons, and we find high condensate fractions at microcavity-plasma temperatures, for experimentally achievable cavity lengths (100-500µm) and photon numbers (10^{10}-10^{12}).

Plasmon dispersion and Landau damping in the nonlinear quantum regime.

We study the dispersion properties of electron plasma waves, or plasmons, which can be excited in quantum plasmas in the nonlinear regime. In order to describe nonlinear electron response to finite amplitude plasmons, we apply the Volkov approach to nonrelativistic electrons. For that purpose, we use the Schrödinger equation and describe the electron population of a quantum plasma as a mixture of quantum states. Within the kinetic framework that we are able to derive from the Volkov solutions, we discuss the role of the wave amplitude on the nonlinear plasma response. Finally, we focus on the quantum properties of nonlinear Landau damping and study the contributions of multiplasmon absorption and emission processes.

Photon bubbles in ultracold matter.

We show that static and oscillating photon bubbles can be excited by diffused light in the laser cooled matter confined in a magneto-optical trap. The bubble instability is due to the coupling between the radiation field and the mean field oscillations of the ultracold gas, and it can provide a source for low frequency turbulence. We consider a diffusion-dominated regime, which can be described by a radiation transport equation, coupled with the mean field equations for the cold atom gas. A perturbative analysis shows the occurrence of two different regimes with either oscillating or purely growing bubbles. This work could also be useful to understand similar processes in astrophysics.

Photon bubble turbulence in cold atom gases.

Turbulent radiation flow is commonplace in systems with strong, incoherent, light-matter interactions. In astrophysical contexts, photon bubble turbulence is considered a key mechanism behind enhanced radiation transport, and its importance has been widely asserted for a variety of high energy objects such as accretion disks and massive stars. Here, we show that analogous conditions to those of dense astrophysical objects can be obtained in large clouds of cold atoms, prepared in a laser-cooling experiment, driven close to a sharp electronic resonance. By accessing the spatially-resolved atom density, we are able to identify a photon bubble instability and the resulting regime of photon bubble turbulence. We also develop a theoretical model describing the coupled dynamics of both photon and atom gases, which accurately describes the statistical properties of the turbulent regime. This study thus opens the possibility of simulating radiation-dominated astrophysical systems in cold atom experiments.

Controlled beat-wave Brillouin scattering in the ionosphere.

Stimulated Brillouin scattering experiments in the ionospheric plasma using a single electromagnetic pump wave have previously been observed to generate an electromagnetic sideband wave, emitted by the plasma, together with an ion- acoustic wave. Here we report results of a controlled, pump and probe beat-wave driven Brillouin scattering experiment, in which an ion-acoustic wave generated by the beating of electromagnetic pump and probe waves, results in electromagnetic sideband waves that are recorded on the ground. The experiment used the EISCAT facility in northern Norway, which has several high power electromagnetic wave transmitters and receivers in the radio frequency range. An electromagnetic pump consisting of large amplitude radio waves with ordinary (O) or extraordinary (X) mode polarization was injected into the overhead ionosphere, along with a less powerful probe wave, and radio sideband emissions observed on the ground clearly show stimulated Brillouin emissions at frequencies agreeing with, and changing with, the pump and probe frequencies. The experiment was simulated using a numerical full-scale model which clearly supports the interpretation of the experimental results. Such controlled beat-wave experiments demonstrate a way of remotely investigating the ionospheric plasma parameters.

Inverse Faraday effect with linearly polarized laser pulses.

The inverse Faraday effect is usually associated with circularly polarized radiation; here, we show that it can also occur for linearly polarized radiation. The quasistatic axial magnetic field generated by a laser propagating in plasma can be calculated by considering both the spin and the orbital angular momenta of the laser pulse. A net spin is present when the radiation is circularly polarized and a net orbital angular momentum is present if there is any deviation from perfect rotational symmetry. The orbital angular momentum gives an additional contribution to the axial magnetic field that can enhance or reduce the effect usually attributed to circular polarization and strongly depends on the intensity profile of the Laguerre-Gaussian modes involving the azimuthal and radial mode numbers.

Plasmon excitations with a semi-integer angular momentum.

We provide an explicit model for a spin-1/2 quasi-particle, based on the superposition of plasmon excitations in a quantum plasmas with intrinsic orbital angular momentum. Such quasi-particle solutions can show remarkable similarities with single electrons moving in vacuum: they have spin-1/2, a finite rest mass, and a quantum dispersion. We also show that these quasi-particle solutions satisfy a criterium of energy minimum.

Modulational instability of spatially broadband nonlinear optical pulses in four-state atomic systems.

The modulational instability of broadband optical pulses in a four-state atomic system is investigated. In particular, starting from a recently derived generalized nonlinear Schrödinger equation, a wave-kinetic equation is derived. A comparison between coherent and random-phase wave states is made. It is found that the spatial spectral broadening can contribute to the nonlinear stability of ultrashort optical pulses. In practical terms, this could be achieved by using random-phase plate techniques.

Tonks-Dattner resonances in a quantum plasma bubble.

We establish the spectrum of Tonks-Dattner mode resonances in a quantum plasma bubble and consider the spectral changes associated with plasma quenching and plasma expansion. The quantum corrections associated with the mode spectrum are specified, which can be used as a diagnostic tool to identify the quantum regime. The frequency shifts associated with time-varying plasma bubbles correspond to time refraction and can also be used as a plasma diagnostic. We also study the energy mode coupling, in the presence of a low-frequency perturbation. It will be shown that the mode coupling equations take the form of generalized Bloch equations, where a nonlinear Rabi frequency can also be identified.

Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering.

Twisted Laguerre-Gaussian lasers, with orbital angular momentum and characterized by doughnut-shaped intensity profiles, provide a transformative set of tools and research directions in a growing range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high-gradient positron acceleration. The production of ultra-high-intensity twisted laser pulses could then also have a broad influence on relativistic laser-matter interactions. Here we show theoretically and with ab initio three-dimensional particle-in-cell simulations that stimulated Raman backscattering can generate and amplify twisted lasers to petawatt intensities in plasmas. This work may open new research directions in nonlinear optics and high-energy-density science, compact plasma-based accelerators and light sources.

Quasi-polaritons in Bose-Einstein condensates induced by Casimir-Polder interaction with graphene.

We consider the mechanical coupling between a two-dimensional Bose-Einstein condensate and a graphene sheet via the vacuum fluctuations of the electromagnetic field which are at the origin of the so-called Casimir-Polder potential. By deriving a self-consistent set of equations governing the dynamics of the condensate and the flexural (out-of-plane) modes of the graphene, we can show the formation of a new type of purely acoustic quasi-particle excitation, a quasi-polariton resulting from the coherent superposition of quanta of flexural and Bogoliubov modes.

Coarctation of the aorta: a new surgical technique.

We developed a new surgical technique to treat coarctation of the aorta. It consists of an aortoplasty in which the left subclavian artery is transected, opened longitudinally, and sutured to the coarctated segment so as to correct the narrowing and also maintain blood flow through the left upper limb.

A new technique for repair of aortic coarctation. Subclavian flap aortoplasty with preservation of arterial blood flow to the left arm.

From February 1984 to March 1986, 28 patients underwent a new technique of coarctation repair. This technique consists of a complete mobilization of the left subclavian artery extended to the origin of its first branches. The aorta need not be extensively mobilized and the intercostal arteries are individually controlled with snares. After all the proper clamping, the left subclavian artery is detached from the aorta at its origin and is opened longitudinally on its posterior aspect. The anterior wall of the aorta is then incised, beginning with the opening at the origin of the left subclavian artery and extending distally to the descending aorta 12 to 15 mm past the coarctation. The coarctation membrane is excised and the ductus is ligated and divided. The opened left subclavian artery, now forming a flap, is pulled down and sutured to the edges of the aorta, widening the coarctation site and also preserving the blood flow to the left arm. The ages of the patients ranged from 2 months to 25 years (mean 4.24 +/- 4.9 years) and their weights ranged from 2.8 to 52 kg (mean: 14.8 +/- 10.0 kg). There were no hospital deaths and the mean follow-up was 9.6 months (+/- 4.9 months). Recatheterization of four patients from 4 to 12 months postoperatively showed adequate correction and strongly suggested normal growth of the aorta at the site of coarctation, as well as preservation of the blood flow through the left subclavian artery. Doppler measurements showed normal flow to the left arm and no gradients through the isthmic area. Our experience indicates that this technique is not only feasible but is the procedure of choice in most cases of discrete isthmic coarctation and in some cases of long narrowing of the isthmus in patients with a wide range of ages and weights.

Cardiac valve replacement with glutaraldehyde preserved aortic allografts.

From September 1984 to December 1988, 144 patients underwent cardiac valve replacement using glutaraldehyde preserved stent mounted aortic allografts. The mean age was 21.4 years (54.9% were 15 years old or younger). The mitral valve was replaced in 125 patients, the aortic valve in 7, the pulmonary valve in 3, the tricuspid in 1, the mitral and tricuspid in 1, and the aortic and mitral in 7. Hospital mortality was 2.8% (4 patients). Total follow-up was 396.3 patient-years and the mean follow-up was 2.8 years per patient. The 5-year actuarial survival was 73.8% +/- 11.9%. The 4-year actuarial survival for patients aged 15 or younger was 81.4% +/- 7.1%. The overall mortality was 2.8% +/- 0.8%/per patient-year. The incidence of valve-related complications was 4.8% +/- 1.1%/per patient-year, and the calcification rate was 3.0% +/- 0.9%/per patient-year and was the main complication reported in 12 patients, all under the age of 15 years. It occurred 14-47 months after implantation (mean 32.7 months). Five-year actuarial freedom from valve dysfunction due to calcification was 82.6% +/- 5.0% and for patients aged 15 or younger was 69.9% +/- 8.8%. The incidence of reoperation was 3.3% +/- 0.9%/per patient-year. These initial results demonstrate a 5-year actuarial freedom from primary valve failure due to fibrocalcification superior to the results obtained with xenobioprostheses in the paediatric age group.

Early surgical results in the treatment of endomyocardial fibrosis. A Brazilian cooperative study.

This report summarizes the surgical experience and early results obtained at four surgical centers in the northeast and south of Brazil. From December 1977 to September 1986, 95 operations were performed on 93 patients, ages 11-59. Bilateral lesions occurred in 42 patients, right lesions in 39, and left lesions in 12. Ventricular decortication and removal of thrombi were performed in all. In right-sided lesions, the tricuspid valve was substituted by a bioprosthesis in 34 cases, and substituted by a tilting disk valve in 1 case. In 4 patients, the valve could be preserved. The left-sided lesions led to valve substition by a bioprosthesis in 11 cases, and preservation of the valve in 1. The bilateral lesions needed bioprosthesis in the mitral position in 37 patients, and a disk valve in 2. In these 39 instances, the valvular procedure was insertion of a tricuspid bioprosthesis. Three tricuspid and three mitral plasties were performed. The overall mortality was 20% (26.2% for bilateral lesions, 14.6% for the right-sided lesions, and 20% for the left-sided lesions). The main cause of death was low cardiac output. Aside from a variable degree of right and left ventricular failure, many other non-fatal complications clouded the postoperative course. Complete AV blocks occurred in 10 cases, with the need for permanent pacing in 7 survivors. The mortality and morbidity in the present series is in keeping with the results reported in current literature. Regarding the advanced stage of their patients' disease, the authors agree with the recommendation for earlier surgical intervention.

Laser propagation in cylindrical waveguides.

Laser propagation in cylindrical waveguides is studied theoretically, assuming that the guide medium and the internal medium have permittivities and identical permeabilities that are uniform in space and time and independent of the fields. Approximate solutions to the cylindrical dispersion relation are found and compared with numerical solutions. For high refractive indices and small radii the modes are transverse electric and transverse magnetic, as in the loss-less case. As the refractive index is lowered or the radius increased the lower-order modes become hybrid electric and hybrid magnetic, and the lower-order transverse magnetic modes are modified. The higher-order modes, in any waveguide, are always transverse. The transition to hybrid modes is marked by the disappearance of the fundamental electric mode and the appearance of an additional magnetic mode. This mode and the losses of the magnetic modes adjacent to it are only adequately described by numerical solutions. The losses of the transverse modes are accurately reproduced by a simple model based on a mean reflectivity.

Resonant quasiparticles in plasma turbulence.

A general view is proposed on wave propagation in fluids and plasmas where the resonant interaction of monochromatic waves with quasiparticles is considered. A kinetic equation for quasiparticles is used to describe the broadband turbulence interacting with monochromatic waves. Resonant interactions occur when the phase velocity of the long wavelength monochromatic wave is nearly equal to the group velocity of short wavelength wave packets, or quasiparticles, associated with the turbulent spectrum. It is shown that quasiparticle Landau damping can take place, as well as quasiparticle beam instabilities, thus establishing a direct link between short and large wavelength perturbations of the medium. This link is distinct from the usual picture of direct and inverse energy cascades, and it can be used as a different paradigm for the fluid and plasma turbulence theories.