Strong light-matter coupling: parametric interactions in a cavity and free-space

We consider parametric interactions of laser pulses in a coherent macroscopic ensemble of resonant atoms, which are possible in the strong coupling regime of light-matter interaction. The spectrum condensation (lasing at collective vacuum Rabi sidebands) was studied in an active cavity configuration. Parametric interactions under the strong light-matter coupling were proved even in free space. In contrast to bichromatic beats in a cavity, they were shown to appear due to interference between polaritonic wave packets of different group velocities.Comment: 4 pages, 2 figure

The new ultra high-speed all-optical coherent streak-camera

In the present paper a new type of ultra high-speed all-optical coherent streak-camera was developed. It was shown that a thin resonant film (quantum dots or molecules) could radiate the angular sequence of delayed ultra-short pulses if a transverse spatial periodic distribution of the laser pump field amplitude has a triangle shape

Coherent interaction of laser pulses in a resonant optically dense extended medium under the regime of strong field-matter coupling

Nonstationary pump-probe interaction between short laser pulses propagating in a resonant optically dense coherent medium is considered. A special attention is paid to the case, where the density of two-level particles is high enough that a considerable part of the energy of relatively weak external laser-fields can be coherently absorbed and reemitted by the medium. Thus, the field of medium reaction plays a key role in the interaction processes, which leads to the collective behavior of an atomic ensemble in the strongly coupled light-matter system. Such behavior results in the fast excitation interchanges between the field and a medium in the form of the optical ringing, which is analogous to polariton beating in the solid-state optics. This collective oscillating response, which can be treated as successive beats between light wave-packets of different group velocities, is shown to significantly affect propagation and amplification of the probe field under its nonlinear interaction with a nearly copropagating pump pulse. Depending on the probe-pump time delay, the probe transmission spectra show the appearance of either specific doublet or coherent dip. The widths of these features are determined by the density-dependent field-matter coupling coefficient and increase during the propagation. Besides that, the widths of the coherent features, which appear close to the resonance in the broadband probe-spectrum, exceed the absorption-line width, since, under the strong-coupling regime, the frequency of the optical ringing exceeds the rate of incoherent relaxation. Contrary to the stationary strong-field effects, the density- and coordinate-dependent transmission spectra of the probe manifest the importance of the collective oscillations and cannot be obtained in the framework of the single-atom model.Comment: 10 pages, 8 figures, to be published in Phys. Rev.

Resonant nonstationary amplification of polychromatic laser pulses and conical emission in an optically dense ensemble of neon metastable atoms

Experimental and numerical investigation of single-beam and pump-probe interaction with a resonantly absorbing dense extended medium under strong and weak field-matter coupling is presented. Significant probe beam amplification and conical emission were observed. Under relatively weak pumping and high medium density, when the condition of strong coupling between field and resonant matter is fulfilled, the probe amplification spectrum has a form of spectral doublet. Stronger pumping leads to the appearance of a single peak of the probe beam amplification at the transition frequency. The greater probe intensity results in an asymmetrical transmission spectrum with amplification at the blue wing of the absorption line and attenuation at the red one. Under high medium density, a broad band of amplification appears. Theoretical model is based on the solution of the Maxwell-Bloch equations for a two-level system. Different types of probe transmission spectra obtained are attributed to complex dynamics of a coherent medium response to broadband polychromatic radiation of a multimode dye laser.Comment: 9 pages, 13 figures, corrected, Fig.8 was changed, to be published in Phys. Rev.

РАЗРАБОТКА И ЭКСПЕРИМЕНТАЛЬНЫЕ ИССЛЕДОВАНИЯ НЕЙРОПОРТА ДЛЯ ТЕРАПИИ ГЛИОМЫ ГОЛОВНОГО МОЗГА

Current paper presents the results of the system development for intracranial implantation aimed on therapy and prevention of brain gliomas relapse. The main property of the system, in prospective,  will be to direct the growth of glioma cells localized in the region  adjacent to the site of the removed tumor along the fi bers towards  the proximal part of the fiber-optic scaffold (neuroport). Such  approach will allow carrying out cells diagnostics by the  photoluminescence signal and provide subsequent destruction of  malignant cells by photodynamic action. Besides, this system could  be used for monitoring the processes occurring in the probed area in order to control the possible relapses. The localization of cells along  the fi ber structures covered with gelatin compound, which is the  source of amino acids during cultivation, was shown during the glioma cells growth dynamics study. Moreover, four different designs of intracranial scaffold models, serving as ports for diagnostic and therapeutic laser radiation delivery, were developed and  successfully tested in the framework of the research. The results  obtained on the rats brain with induced tumors (glioma C6) after  neuroport implantation demonstrate sufficiently intense fluorescence in the tumor bed after intravenous injection of the  nonmetallic sulfonated phthalocyanine based photosensitizer, and a  pronounced photodynamic effect leading to total destruction of the  tumor. In this way, the results of this study open the prospects of creating the neuroport with an internal fi ber structure that focuses the glioma cells growth.В работе представлены результаты разработки системы для внутричерепной имплантации с целью терапии и предотвращения рецидивирования глиом головного. Основное свойство  системы в перспективе будет состоять в том, чтобы направить рост клеток глиомы,  локализованных в области, прилегающей к месту удаленной опухоли, вдоль волокон по  направлению к проксимальной части волоконно-оптического имплантата (нейропорт) с  целью их регистрации по сигналу фотолюминесценции и последующей их деструкции в  результате фотодинамического воздействия. Такое устройство должно обеспечить  мониторинг процессов, происходящих в зондируемой области с целью контроля процессов  рецидивирования. В ходе данного исследования динамики роста клеток глиомы показана  локализация клеток вдоль волоконных структур, покрытых желатином, который является  источником аминокислот при культивировании. Также в ходе работы были разработаны и  успешно апробированы четыре различных конструкции макетов внутричерепных  имплантатов, выполняющие роль портов для доставки диагностического и терапевтического лазерного излучения. Получены на головном мозге крыс с индуцированными опухолями  (глиома С6) после имплантации нейропорта, демонстрирующие достаточно интенсивную  флуоресценцию в ложе опухоли при внутривенном введении фотосенсибилизатора на  основе безметального сульфированного фталоцианина и выраженный фотодинамический  эффект, приведший к тотальному разрушению опухоли. Полученные результаты открывают  перспективы создания нейропорта с внутренней волоконной структурой, фокусирующей рост клеток глиомы

Hall-plot of the phase diagram for Ba(Fe₁₋ₓCoₓ)₂As₂

The Hall effect is a powerful tool for investigating carrier type and density. For single-band materials, the Hall coefficient is traditionally expressed simply by , where e is the charge of the carrier, and n is the concentration. However, it is well known that in the critical region near a quantum phase transition, as it was demonstrated for cuprates and heavy fermions, the Hall coefficient exhibits strong temperature and doping dependencies, which can not be described by such a simple expression, and the interpretation of the Hall coefficient for Fe-based superconductors is also problematic. Here, we investigate thin films of Ba(Fe₁₋ₓCoₓ)₂As₂ with compressive and tensile in-plane strain in a wide range of Co doping. Such in-plane strain changes the band structure of the compounds, resulting in various shifts of the whole phase diagram as a function of Co doping. We show that the resultant phase diagrams for different strain states can be mapped onto a single phase diagram with the Hall number. This universal plot is attributed to the critical fluctuations in multiband systems near the antiferromagnetic transition, which may suggest a direct link between magnetic and superconducting properties in the BaFe₂As₂ system

Multiscale modelling for fusion and fission materials: the M4F project

The M4F project brings together the fusion and fission materials communities working on the prediction of radiation damage production and evolution and its effects on the mechanical behaviour of irradiated ferritic/martensitic (F/M) steels. It is a multidisciplinary project in which several different experimental and computational materials science tools are integrated to understand and model the complex phenomena associated with the formation and evolution of irradiation induced defects and their effects on the macroscopic behaviour of the target materials. In particular the project focuses on two specific aspects: (1) To develop physical understanding and predictive models of the origin and consequences of localised deformation under irradiation in F/M steels; (2) To develop good practices and possibly advance towards the definition of protocols for the use of ion irradiation as a tool to evaluate radiation effects on materials. Nineteen modelling codes across different scales are being used and developed and an experimental validation programme based on the examination of materials irradiated with neutrons and ions is being carried out. The project enters now its 4th year and is close to delivering high-quality results. This paper overviews the work performed so far within the project, highlighting its impact for fission and fusion materials science.This work has received funding from the Euratom research and training programme 2014-2018 under grant agreement No. 755039 (M4F project)