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The conclusion of the Expert Council presents the results of discussing the diagnosis and therapy of interstitial lung diseases in systemic scleroderma. The reason for this discussion was the emergence of new data on the use of nintedanib in this category of patients.

This article studies the generation of terahertz (THz) radiation in carbon dioxide ( ${\bf CO_2}$ ) at different levels of gas pressure. It was demonstrated that under low gas pressure, optical-terahertz conversion can be adequately described by a simplified photocurrent model. However, with the increase of gas pressure, the contribution of intra-atomic nonlinearities as a source of terahertz response irradiated by a two-color laser field is growing. Moreover, at high levels of gas pressure, the interference and dispersive effects should be taken into consideration as well. The proposed model allows for the optimization of experimental conditions aimed at flexible control of intensity and spectral properties of THz radiation.

We report numerically the role of the focusing on the generation of anti-Stokes wing and harmonics in fluorites (CaF 2 ) during the propagation of mid-IR femtosecond laser pulses. We show the increase of electron plasma density and intensity of the generated spectrum short-wavelength region under tighter focusing condition.

We present a novel approach for flexible adjustment of the media nonlinear response for efficient harmonics generation. Molecular resonances located in mid-IR have shown to change refractive index for pump radiation significantly and provide opportunity for effective phase matching. We use mixture containing 48 bar of xenon (Xe) and 1 bar of carbon dioxide (CO 2 ) to generate eleven harmonics with efficiency of 1% for third harmonic and 0.3% for higher ones (from 5th to 11th) in total. Theoretical calculations predict simultaneous phase matching of large number of harmonics in XUV region paving the way for seeding FELs and pump-probe XUV diagnostic.

A concept of an electrically tunable resonance detector of THz-frequency signals based on antiferromagnetic/heavy metal (AFM/HM) hetero-structure is proposed. The conversion of a THz-frequency input signal into DC voltage is done using the inverse spin Hall effect in an (AFM/HM) bilayer. An additional bias DC current in the HM layer can be used to vary the effective anisotropy of the AFM, and, therefore, to tune the AFMR frequency. The proposed AFM/HM hetero-structure works as a resonance-type quadratic detector which can be tuned by the bias current in the range of at least 10 percent of the AFMR frequency and our estimations show that the sensitivity of this detector could be comparable to that of modern detectors based on the Schottky, Gunn or graphene-based diodes.

We compare experimental and theoretical studies of the quasi-phase matching (QPM) of high-order harmonic generation (HHG) during propagation of two-color pulses through the indium multi-jet plasmas. Role of the sizes of plasma jets and distance between them on the HHG efficiency at QPM conditions is analyzed. The results of the QPM conditions’ studies provide the reliable interpretation of this phenomenon.

In this paper, we propose an approximate nonlinear theory of a spintronic terahertz-frequency oscillator based on antiferromagnet-heavy metal interfaces. We present a model of excitation of nonlinear oscillations of Neel vector in an antiferromagnet under the action of terahertz pulses of an electromagnetic field. We determine that, with increasing pumping pulse amplitude, the spin system response increases nonlinearly in the fundamental quasi-antiferromagnetic mode. Our results theoretically show that a spin-current flowing from a heavy metal due to the spin-Hall effect vary the frequencies of the output EM oscillations in a wide range, which could be detected by a standard pump-and-probe spectroscopy. Our study paves the way to laser-induced, electrically tunable, low-power, ultrafast AFM-based oscillator that operates without external magnetic fields at room temperature for telecommunication systems, bio-inspired networks and optical networks on chip. The nonlinear dynamics of the antiferromagnet-based emitters discussed here is of importance in terahertz-frequency spintronic technologies.

Novel methods of coherent short-wavelength sources generation require thorough analysis for their further amendments and practical implementations. In this work, we report on the quasi-phase matching (QPM) of high-order harmonics generation during the propagation of single- and two-color femtosecond pulses through multi-jet plasmas, which allows the enhancement of groups of harmonics in different ranges of extreme ultraviolet. The role of the number of coherent zones, sizes of plasma jets and the distance between them, plasma formation conditions, and the characteristics of the fundamental radiation on the harmonic efficiency at quasi-phase matching (QPM) conditions are analyzed. We demonstrate the ~40&times, enhancement factor of the maximally-enhanced harmonic with respect to the one generated at ordinary conditions in the imperforated plasma.

We report on the numerical investigation of spectral enrichment under mid-infrared (4.4 μm) laser filamentation in CaF2 and the influence of the external focusing on this nonlinear phenomenon. It is shown that the supercontinuum generation is related to the rapid free-electron increase and appears when nonlinear and diffraction lengths are practically the same. With further pulse propagation, the anti-Stokes wing (ASW) is formed which is caused by the pulse splitting. Looser focusing leads to pulse splitting be closer to the point of supercontinuum formation along the propagation axis. The ASW experiences a red-shift when external focusing is applied due to increased free-electron density.

We report an asymmetric Raman-initiated temporal splitting and spectrum transformation of intense 200 fs laser pulses with normal (1.24 μm) and anomalous (1.9 μm) group velocity dispersion in YAG crystal.

One of the promising methods of the terahertz (THz) radiation generation is the use of the two-color laser field (ω-2ω) focused in the gas medium [1]. Typically, the polarization of the low frequency THz field generated in gas is linear [2], but, in some conditions, it can be elliptical due to modulation of the laser pulse phase and its polarization in the gas plasma [3]. For some practical applications, it is useful to have the elliptically polarized THz radiation. Usually, methods based on the mixing of the elliptically polarized ω with a linear (or elliptically polarized) 2ω, producing low-frequency elliptically polarized THz emission (

A theory of the nonlinear optical response of an atom interacting with a superposition of arbitrarily polarized fields is developed. The theory is based on the analytical solution of the boundary-value problem for an electron moving in a spherically symmetric intraatomic field and in the field of an external electromagnetic field. By means of the example of an argon atom interacting with a bichromatic field formed by the first and second harmonics of a Ti:sapphire laser, it is shown that, when an atom interacts with the field of two polarized pulses the polarization directions of which are not collinear, the response spectrum significantly depends on the laser radiation parameters—the duration and intensity of pulses, the time of delay between them, and the angle between the directions of polarization vectors. Generation of THz radiation is shown to be possible in the ionization-free regime due to intraatomic nonlinearity.

We compare the results of experimental and theoretical studies of the quasi-phase matching (QPM) of high-order harmonic generation (HHG) during propagation of two-color femtosecond pulses through the indium multi-jet plasmas. The role of number of coherent zones and size of plasma jets on the HHG efficiency at QPM conditions is analysed. We demonstrate the enhancement of the HHG efficiency due to QPM during laser-plasma interaction.

We report on numerical study of the nonlinear pulse propagation under filamentation of femtosecond near-infrared radiation under normal dispersion regime in YAG crystal. Influence of the Raman and Kerr tandem action on a spatial and temporal dynamics of the laser pulse were discussed. We have shown that Raman nonlinearity provides an asymmetry of temporal pulse profile: the leading edge becomes more bright and propagates at larger distances in comparison with trailing edge. Keywords: filamentation, supercontinuum generation, Raman nonlinearity.

International audience; Recent advances in high-harmonic generation gave rise to soft X-ray pulses with higher intensity, shorter duration and higher photon energy. One of the remaining shortages of this source is its restriction to linear polarization, since the yield of generation of elliptically polarized high harmonics has been low so far. We here show how this limitation is overcome by using a cross-polarized two-colour laser field. With this simple technique, we reach high degrees of ellipticity (up to 75%) with efficiencies similar to classically generated linearly polarized harmonics. To demonstrate these features and to prove the capacity of our source for applications, we measure the X-ray magnetic circular dichroism (XMCD) effect of nickel at the M2,3 absorption edge around 67 eV. There results open up the way towards femtosecond time-resolved experiments using high harmonics exploiting the powerful element-sensitive XMCD effect and resolving the ultrafast magnetization dynamics of individual components in complex materials.

High harmonic generation in gases is developing rapidly as a soft X-ray femtosecond light-source for applications. This requires control over all the harmonics characteristics and in particular, spatial properties have to be kept very good. In previous literature, measurements have always included several harmonics contrary to applications, especially spectroscopic applications, which usually require a single harmonic. To fill this gap, we present here for the first time a detailed study of completely isolated harmonics. The contribution of the surrounding harmonics has been totally suppressed using interferential filtering which is available for low harmonic orders. In addition, this allows to clearly identify behaviors of standard odd orders from even orders obtained by frequency-mixing of a fundamental laser and of its second harmonic. Comparisons of the spatial intensity profiles, of the spatial coherence and of the wavefront aberration level of 5ω at 160 nm and 6ω at 135 nm have then been performed. We have established that the fundamental laser beam aberrations can cause the appearance of a non-homogenous donut-shape in the 6ω spatial intensity distribution. This undesirable effect can be easily controlled. We finally conclude that the spatial quality of an even harmonic can be as excellent as in standard generation.

We report both theoretical and experimental results on cut-off frequency saturation as function of laser pulse intensity for the high optical harmonics generated in silver plasma. The sequential quantum-mechanical theory is used for theoretical description

We present the results of the numerical study of the generation of the elliptical terahertz (THz) radiation by an extended argon gas media interacting with a two-color laser field. On the base of a single-atom response to the action of the two-color laser field with a linear polarization of each of the components of the laser field and different angles between them, two angles (90° and 45°) and radiation at two frequencies (56 and 29 THz) corresponding to them and having relatively high values of ellipticities have been chosen for the calculation of the extended gas response. The results obtained for different widths and lengths (up to 20 cm) of the gas demonstrate the cone structure of the generated radiation together with a non-monotonical distribution of the ellipticity. Methods of control of the value of the ellipticity are presented and discussed. The single-atom investigations have been carried out with the help of the non-perturbative theory for the ionization-free regime of interaction.

We present the results of theoretical study on the effective generation of both terahertz radiation and high-order harmonics in the process of a single atom interaction with a multicolor laser field. Numerical results are discussed.

The interaction between high intensity ultrashort laser pulses and the atomic gas in the ionization-free regime leads to the emission of coherent, short pulse radiation at terahertz frequency. In this work we discuss a model for this effect and its experimental realization.

The specific features of the terahertz (THz) emission from the extended media illuminated by the two-color laser fields is studied. It is shown that due to dispersion effects the amplitude of the response THz field varies periodically with the travelled distance. These spatial variations manifest themselves in the angular spectra of THz emission and, as a result, the integral efficiency of the THz emission depends significantly on the medium geometry. The origin of such behavior is in the variation of the relative phase of ω and 2ω components of the laser field. The THz intensity dependence on the relative phase between the fundamental and the second harmonics for two gases (Ne and Ar), two seed lasers (Ti:Sa and Cr:F) and two angles between the polarization of two-color laser field components (0 and π/2) is investigated quantum-mechanically, and it is confirmed that the optimal phase for the THz generation is π/2 for all described cases.