Vacuum breakdown in magnetic dipole wave by 10-PW class lasers.

The vacuum breakdown by 10-PW-class lasers is studied in the optimal configuration of laser beams in the form of an m-dipole wave, which maximizes the magnetic field. Using 3D PIC simulations we calculated the threshold of vacuum breakdown, which is about 10 PW. We examined in detail the dynamics of particles and identified particle trajectories which contribute the most to vacuum breakdown in such highly inhomogeneous fields. We analyzed the dynamics of the electron-positron plasma distribution on the avalanche stage. It is shown that the forming plasma structures represent concentric toroidal layers and the interplay between particle ensembles from different spatial regions favors vacuum breakdown. Based on the angular distribution of charged particles and gamma photons a way to experimentally identify the process of vacuum breakdown is proposed.

Particle trajectories, gamma-ray emission, and anomalous radiative trapping effects in magnetic dipole wave.

In studies of interaction of matter with laser fields of extreme intensity there are two limiting cases of a multibeam setup maximizing either the electric field or the magnetic field. In this work attention is paid to the optimal configuration of laser beams in the form of an m-dipole wave, which maximizes the magnetic field. We consider in such highly inhomogeneous fields the advantages and specific features of laser-matter interaction, which stem from individual particle trajectories that are strongly affected by gamma photon emission. It is shown that in this field mode qualitatively different scenarios of particle dynamics take place in comparison with the mode that maximizes the electric field. A detailed map of possible regimes of particle motion (ponderomotive trapping, normal radiative trapping, radial, and axial anomalous radiative trapping), as well as angular and energy distributions of particles and gamma photons, is obtained in a wide range of laser powers up to 300 PW, and it reveals signatures of radiation losses experimentally detectable even with subpetawatt lasers.

[Proton magnetic resonance spectroscopy in children with atypical autism comorbid with psychomotor disinhibition syndrome]. / Protonnaya magnitno-rezonansnaya spektroskopiya u detei s atipichnym autizmom, sochetayushchimsya s sindromom psikhomotornoi rastormozhennosti.

OBJECTIVE: To study the relationship of N-acetylaspartate (NAA) metabolism and choline (Cl) metabolism in different parts of the brain based on magnetic resonance spectrography (1H-MRS) with clinical manifestations of autism spectrum disorders (ASD). MATERIAL AND METHODS: Twenty-two children (16 boys, 6 girls), aged 2-10 years, were studied. Russian-language adapted versions of the Autism Treatment Evaluation Checklist (ATEC) and the Nisonger Child Behavior Rating Form (NCBRF) were administered. The ratio of metabolites NAA/creatine (Cr), Cho/Cr, Cho/NAA in the prefrontal cortex, postcentral gyrus and temporal lobes was studied using 1H-MRS. RESULTS: The following correlations were found: 1) between the NAA/Cr value and the Sensory/Cognitive Awareness scale in the prefrontal cortex on the left (ρ=0.479) and on the right (ρ=0.483); the Health/Physical Behavior scale in the precentral gyrus on the left (ρ=0.572) and on the right (ρ=0.463); the Sociability scale in the temporal lobe on the left (ρ=0.481) and on the right (ρ=0.796); the Speech/Language/Communication scale in the right temporal lobe (ρ=-0.552); 2) between the Cho/Cr value and the Adaptive Social scale in the postcentral gyrus on the left (ρ=-0.466) and on the right (ρ=-0.518); the Compliant/Calm scale in the prefrontal cortex on the right (ρ=0.624) and on the left (ρ=-0.541); 3) between the Cho/NAA ratio and the Speech/Language/Communication scale in the right pre-central (ρ=-0.471) and post-central gyrus (ρ=-0.507); the Self-Isolated/Ritualistic¼ scale in the left (ρ=-0.486) and right temporal lobe (ρ=-0.596). CONCLUSIONS: Thus, the predominant localization of disorders of N-acetylaspartate metabolism in communication disorders (bilaterally in the temporal lobes), cognitive, behavioral and somatic manifestations (bilaterally in the prefrontal regions) was established. Increased CI metabolism has identified deficits in interaction skills in both postcentral gyrus, and reveals bilateral differences in the effect on behavioral control in the prefrontal cortex. The results confirm the previously established numerous patterns between abnormal activation of the prefrontal cortex and neuronal dysfunction in ASD. But unlike other studies, it was possible to trace these relationships within a narrower phenotype of disorders - atypical autism comorbid with psychomotor disinhibition.

Laser-driven plasma pinching in e

The cascaded production and dynamics of electron-positron plasma in ultimately focused laser fields of extreme intensity are studied by three-dimensional particle-in-cell simulations with the account of the relevant processes of quantum electrodynamics (QED). We show that, if the laser facility provides a total power above 20 PW, it is possible to trigger not only a QED cascade but also pinching in the produced electron-positron plasma. The plasma self-compression in this case leads to an abrupt rise of the peak density and magnetic (electric) field up to at least 10^{28}cm^{-3} and 1/20 (1/40) of the Schwinger field, respectively. Determining the actual limits and physics of this process might require quantum treatment beyond the used standard semiclassical approach. The proposed setup can thus provide extreme conditions for probing and exploring fundamental physics of the matter and vacuum.

Impact of quantum effects on relativistic electron motion in a chaotic regime.

The impact of quantum effects on electron dynamics in a plane linearly polarized standing wave with relativistic amplitudes is considered. Using spectral analysis of Lyapunov characteristic exponents with and without radiation losses we show that the contraction effect of phase space due to the radiation reaction force in the classical form does not occur in the quantum case when the discreteness of photon emission is taken into account. It is also demonstrated that electron bunch kinetics has a diffusion solution rather than the d'Alambert type solution as in the classical description. For this case, we applied the Markov chain formalism and showed that this method gives exact characteristics of electron bunch evolution, such as motion of the center of mass and electron bunch dimensions.

Picosecond Raman compression laser at 1530 nm with aberration compensation.

A passively Q-switched Nd:YAG laser with a master-oscillator power-amplifier configuration based on Brillouin and Raman pulse compression has been developed. The laser operates at 100 Hz repetition rate, producing 50 mJ pulses of approximately 30 ps duration at 1530 nm wavelength with near-diffraction-limited beam quality (M2≤1.2). The effect of spherical aberration in thermally loaded Nd:YAG rods was studied, and efficient aberration compensation was achieved by use of a specially designed aspheric element.

Ultrarelativistic nanoplasmonics as a route towards extreme-intensity attosecond pulses.

The generation of ultrastrong attosecond pulses through laser-plasma interactions offers the opportunity to surpass the intensity of any known laboratory radiation source, giving rise to new experimental possibilities, such as quantum electrodynamical tests and matter probing at extremely short scales. Here we demonstrate that a laser irradiated plasma surface can act as an efficient converter from the femto- to the attosecond range, giving a dramatic rise in pulse intensity. Although seemingly similar schemes have been described in the literature, the present setup differs significantly from the previous attempts. We present a model describing the nonlinear process of relativistic laser-plasma interaction. This model, which is applicable to a multitude of phenomena, is shown to be in excellent agreement with particle-in-cell simulations. The model makes it possible to determine a parameter region where the energy conversion from the femto- to the attosecond regime is maximal. Based on the study we propose a concept of laser pulse interaction with a target having a groove-shaped surface, which opens up the potential to exceed an intensity level of 10(26) W/cm(2) and observe effects due to nonlinear quantum electrodynamics with upcoming laser sources.

Multicascade proton acceleration by a superintense laser pulse in the regime of relativistically induced slab transparency.

The regime of multicascade proton acceleration during the interaction of a 10(21)-10(22) W/cm2 laser pulse with a structured target is proposed. The regime is based on the electron charge displacement under the action of laser ponderomotive force and on the effect of relativistically induced slab transparency which allows realization of the idea of multicascade acceleration. It is shown that a target comprising several thin foils properly spaced apart can optimize the acceleration process and give at the output a quasi-monoenergetic beam of protons with energies up to hundreds of MeV with an energy spread of just a few percent.

Optical coherent tomography for in vivo determination of changes in hair cross section and diameter during treatment with glucocorticosteroids--a simple method to screen for doping substances?

Eighty percent of hair follicles are in the growing phase. They grow approximately 0.3 mm/day. The hair follicles are surrounded by a close network of capillaries, which supplies them with nutrients. It is well known that substances which influence the metabolic processes of humans also influence hair growth. Steroids, which are used for doping in sport, are among these substances. In the present paper, optical coherent tomography is used for the analysis of changes in the hair structure during the application of steroids for the treatment of patients suffering from auto-immune diseases. Significant differences in the hair cross section could be detected during treatment, while the shape of the hairs was not influenced. It could be demonstrated that optical coherence tomography is a suitable, non-invasive and low-cost measuring technique that can be applied for doping control and screening. As a result of this screening process, only those athletes who show abnormalities in hair parameters would need to be investigated by classical analytical methods. The results presented in this study are not only important for doping controls, but also for several clinical applications, such as therapy and compliance control in cases where the applied substances induce changes in the hair structure.

200 TW 45 fs laser based on optical parametric chirped pulse amplification.

200 TW peak power has been achieved experimentally using a Cr:forsterite master oscillator at 1250 nm, a stretcher, three optical parametrical amplifiers based on KD*P (DKDP) crystals providing 14.5 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor. The final parametrical amplifier and the compressor are described in detail. Scaling of such architecture to multipetawatt power is discussed.

Two-dimensional theory of Cherenkov radiation from short laser pulses in a magnetized plasma.

The Cherenkov wakes excited by intense laser drivers in a perpendicularly magnetized plasma are a potential source of high-power terahertz radiation. We present a two-dimensional (2D) theory of the emission of magnetized wakes excited by a short laser pulse. The 2D model reveals the important role of the transverse size of the laser pulse missed in previous simple one-dimensional estimations of the radiation. We derived expressions for the radiated fields and for the angular/frequency distribution of the radiated energy. Beats in the radiation pattern behind the moving pulse are predicted and explained. For the interpretation of existing experimental results, the time dependence of the energy flux parallel and perpendicular to the laser path is examined.

Optical coherence tomography monitoring for laser surgery of laryngeal carcinoma.

BACKGROUND AND OBJECTIVES: The goal of this study is to apply a new bioimaging modality, the Optical Coherence Tomography (OCT), for intraoperative control in laser surgery of laryngeal carcinoma. STUDY DESIGN/MATERIALS AND METHODS: We studied 26 patients with laryngeal carcinoma in situ and in T(1), T(2) stage. We used an endoscopic OCT device for imaging at a wavelength of 0.83 microm with the acquisition rate of approximately 0.5 frames/s for a single (200 x 200 pixel) tomogram. All patients were operated with a surgical YAG:Nd laser at two switchable wavelengths of 1.44 microm and 1.32 microm by laryngofissure, direct microlaryngoscopy, and fibrolaryngoscopy. RESULTS: Information on structural alterations in laryngeal mucosa to the depth of 2 mm, obtained by OCT, makes it possible to precisely locate tumor borders, thus giving an opportunity to control the surgical treatment of laryngeal carcinoma. The YAG:Nd laser scalpel with wavelengths of 1.32 microm and 1.44 microm is successful in surgical procedures both in open and closed larynx due to efficient coagulation and minimization of collateral tissue damage area. Combination of the two wavelengths in the single laser unit and intraoperative OCT monitoring result is a new modality for minimally invasive larynx surgery. CONCLUSIONS: OCT is promising to become a new diagnosing method of laryngeal carcinoma and a tool for laser treatment monitoring.

[Recovery process after the diphtheric polyneuropathy according to interference electromyography]. / Vosstanovitel'nyi protsess pri difteriinoi polinevropatii po dannym interferentsionnoi élektromyogrammy.

In order to control the recovery process after diphtheric polyneuropathy the dynamics of activity of m.flexor carpi radialis with increasing force was repetitively investigated in 12 patients using surface electromyography (EMG). In patients examined 12.4 +/- 2.9 months after the onset of diphtheria neurogenic type of EMG (decreased amplitude and number of turns along with increasing force) was established. 11-14 months later clinical improvement followed by positive changes of EMG parameters was documented.

In vivo optical coherence tomography imaging of human skin: norm and pathology.

BACKGROUND/AIMS: Since the majority of skin diseases are known to be accompanied by structural alterations, research efforts are focused on the development of various novel diagnostic techniques capable of providing in vivo information on the skin structure. An essential parameter here is spatial resolution. In this paper we demonstrate the capabilities of optical coherence tomography (OCT) in detecting in vivo specific features of thin and thick skin. A particular focus is made on the identification of OCT patterns typical of certain pathological processes in skin, by performing parallel histological and tomographical studies. METHODS: To obtain images of the skin, we used a compact fiber OCT system developed at the Institute of Applied Physics of the Russian Academy of Sciences. A low coherence source (superluminescent diode) operated at a wavelength of 1280 nm; the output power was 0.5-2 mW. This power is low enough to conform to the ANSI safety standards for light exposure. The in-depth resolution limited by the spectral bandwidth (40-50 nm) of the probing light was approximately 20 &mgr;m. The lateral resolution determined by the probe light focusing ranged from 15 to 30 &mgr;m. In this series of experiments the maximum depth of imaging did not extend beyond 1.5 mm. Obtaining images of skin regions 2-6 mm long took 2-4 s. OCT capabilities for imaging normal skin of different localization and some skin diseases were studied in 12 healthy volunteers and 24 patients. RESULTS: OCT imaging of the skin can detect in vivo such general pathological reactions of the human body as active inflammation and necrosis. OCT is useful for in vivo diagnosis of some specific processes in the skin, including hyperkeratosis, parakeratosis and formation of intradermal cavities. OCT imaging is noninvasive and therefore allows frequent multifocal examination of skin without any adverse effects. OCT can perform monitoring of disease progress and recovery in the course of therapy. Morphometric studies, measurements of the depth and extension of skin pathology within the human body can be easily performed by OCT. CONCLUSIONS: OCT allows imaging of subsurface soft tissues with the spatial resolution of 15-20 &mgr;m, a resolution one order of magnitude higher than that provided by other clinically available noninvasive diagnostic techniques. An imaging depth of up to 1.5-2 mm, given by current OCT technology, is sufficient to examine the skin. Real time OCT imaging can provide information not only on the structure, but also on some specific features in the functional state, of tissues. OCT imaging is a noninvasive technique, i.e., OCT does not cause trauma and has no side effects since it utilizes radiation in the near infrared wavelength range at a power as low as 1 mW.

In vivo detection of experimentally induced cortical dysgenesis in the adult rat neocortex using optical coherence tomography.

Imaging cerebral structure in vivo can be accomplished by many methods, including MRI, ultrasound, and computed tomography. Each offers advantages and disadvantages with respect to the others, but all are limited in spatial resolution to millimeter-scale features when used in routine applications. Optical coherence tomography (OCT) is a new, high resolution imaging technique which uses light to directly image living tissue. Here, we investigate the potential use of OCT for structural imaging of the fully developed mammalian cerebral cortex. In particular, we show that OCT can perform in vivo detection of neocortex and differentiate normal and abnormal cortical anatomy. We present the results of detailed optical coherence tomographic (OCT) observations of both normal and abnormal rat neocortex obtained in vivo. Comparative histologic analysis shows excellent correlation with the OCT tomograms.

[Plastic surgery using split skin flap in the primary surgical treatment of crural injuries]. / Plastika rasshcheplennym kozhnym loskutom pri pervichnoi khirurgicheskoi obrabotke povrezhdenii goleni.

An experience with skin plasty in 127 patients is described. Special attention is called to necessary excision of non-viable tissues in fractures of the skin bone and reapplication of the rejected skin.