Raman Lasing and Transverse Mode Selection in a Multimode Graded-Index Fiber with a Thin-Film Mirror on Its End Face.

Multimode fibers are attractive for high-power lasers if transverse modes are efficiently controlled. Here, a dielectric thin-film mirror (R~20%) is micro-fabricated on the central area of the end face of a 1 km multimode 100/140 µm graded-index fiber and tested as the output mirror of a Raman laser with highly multimode (M~34) 940 nm diode pumping. In the cavity with highly reflective input FBG, Raman lasing of the Stokes wave at 976 nm starts at the threshold pump power of ~80 W.

Reversal of crystallization in cryoprotected samples by laser editing.

Advances in cryobiology techniques commonly target either the cooling or the warming cycle, while little thought has been given to ≪repair≫ protocols applicable during cold storage. In particular, crystallization is the dominant threat to cryopreserved samples but proceeds from small nuclei that are innocuous if further growth is forestalled. To this end, we propose a laser editing technique that locally heats individual crystals above their melting point by a focused nanosecond pulse, followed by amorphization during rapid resolidification.

Standard operating procedure to reveal prostate cancer specific volatile organic molecules by infrared spectroscopy.

The growing number of prostate cancer cases is a real concern in modern society. Over 1.4 million new cases and about 400 thousand (>26%) deaths were registered worldwide in 2020 due to prostate cancer.

Self-pressurised rapid freezing at arbitrary cryoprotectant concentrations.

Self-pressurised rapid freezing (SPRF) has been proposed as a simple alternative to traditional high-pressure freezing (HPF) protocols for vitrification of biological samples in electron microscopy and cryopreservation applications. Both methods exploit the circumstance that the melting point of ice reaches a minimum when subjected to pressure of around 210 MPa, however, in SPRF its precise quantity depends on sample properties and hence, is generally unknown. In particular, cryoprotective agents (CPAs) are expected to be a factor; though eschewed by many SPRF experiments, vitrification of larger samples notably cannot be envisaged without them.

Towards Topology-Free Programming for Cyber-Physical Systems with Process-Oriented Paradigm.

The paper proposes a topology-free specification of distributed control systems by means of a process-oriented programming paradigm. The proposed approach was characterized, on the one hand, by a topologically independent specification of the control algorithm and, on the other hand, by the possibility of using existing formal verification methods by preserving the semantics of a centralized process-oriented program. The paper discusses the advantages of a topologically independent specification of distributed control systems, outlines the features of control software, argues why the use of a process-oriented approach to the development of the automation of cyber-physical systems is suitable for solving these problems, describes a general scheme for implementing a distributed control system according to a process-oriented specification, and proposes a formal heuristic algorithm for partitioning a sequential process-oriented program into independent clusters.

Metastable states in the J_{1}-J_{2} Ising model.

We study the J_{1}-J_{2} Ising model on the square lattice using the random local field approximation (RLFA) and Monte Carlo (MC) simulations for various values of the ratio p=J_{2}/|J_{1}| with antiferromagnetic coupling J_{2}, ensuring spin frustration. RLFA predicts metastable states with zero order parameter (polarization) at low temperature for p∈(0,1). This is supported by our MC simulations, in which the system relaxes into metastable states with not only zero, but also with arbitrary polarization, depending on its initial value, external field, and temperature.

2D Temperature Field Reconstruction Using Optical Frequency Domain Reflectometry and Machine-Learning Algorithms.

We present experimental results on the reconstruction of the 2D temperature field on the surface of a 250 × 250 mm sensor panel based on the distributed frequency shift measured by an optical backscatter reflectometer. A linear regression and a feed-forward neural network algorithm, trained by varying the temperature field and capturing thermal images of the panel, are used for the reconstruction. In this approach, we do not use any information about the exact trajectory of the fiber, material properties of the sensor panel, and a temperature sensitivity coefficient of the fiber.

Fundamentals of Fast Tsunami Wave Parameter Determination Technology for Hazard Mitigation.

This paper describes two basic elements of the smart technology, allowing us to bring to a new level the problem of early warning and mitigation of tsunami hazards for the so-called near zone events (when a destructive tsunami wave reaches the nearest coast in tens of minutes after the earthquake). The sensors system, installed in a reasonable way (to detect a wave as early as possible), is capable of transmitting the necessary raw data (measured wave profile) in a real time mode to a processing center. The smart (based on mathematical theory) algorithm can reconstruct an actual source shape within a few seconds using just a part of the measured wave record.

Thermalization of Orbital Angular Momentum Beams in Multimode Optical Fibers.

We report on the thermalization of light carrying orbital angular momentum in multimode optical fibers, induced by nonlinear intermodal interactions. A generalized Rayleigh-Jeans distribution of asymptotic mode composition is obtained, based on the conservation of the angular momentum. We confirm our predictions by numerical simulations and experiments based on holographic mode decomposition of multimode beams.

Single-particle and collective excitations of polar water molecules confined in nano-pores within a cordierite crystal lattice.

Recently, the low-temperature phase of water molecules confined within nanocages formed by the crystalline lattice of water-containing cordierite crystals has been reported to comprise domains with ferroelectrically ordered dipoles within the , -planes which are antiferroelectrically alternating along the -axis. In the present work, comprehensive broad-band dielectric spectroscopy is combined with specific heat studies and molecular dynamics and Monte Carlo simulations in order to investigate in more detail the collective modes and single-particle excitations of nanoconfined water molecules. From DFT-MD simulations we reconstruct the potential-energy landscape experienced by the HO molecules.

Solitonic model of the condensate.

We consider a spatially extended box-shaped wave field that consists of a plane wave (the condensate) in the middle and equals zero at the edges, in the framework of the focusing one-dimensional nonlinear Schrodinger equation. Within the inverse scattering transform theory, the scattering data for this wave field is presented by the continuous spectrum of the nonlinear radiation and the soliton eigenvalues together with their norming constants; the number of solitons N is proportional to the box width. We remove the continuous spectrum from the scattering data and find analytically the specific corrections to the soliton norming constants that arise due to the removal procedure.

Spatio-spectral beam control in multimode diode-pumped Raman fibre lasers via intracavity filtering and Kerr cleaning.

Multimode fibres provide a promising platform for boosting the capacity of fibre links and the output power of fibre lasers. The complex spatiotemporal dynamics of multimode beams may be controlled in spatial and temporal domains via the interplay of nonlinear, dispersive and dissipative effects. Raman nonlinearity induces beam cleanup in long graded-index fibres within a laser cavity, even for CW Stokes beams pumped by highly-multimode laser diodes (LDs).

Diffractive Sensor Elements for Registration of Long-Term Instability at Writing of Computer-Generated Holograms.

The research and development of methods using of the specialized diffractive microstructure sensors embedded in the pattern of computer-generated holograms (CGH) manufactured on circular and X-Y laser writing systems is discussed. These microstructures consist of two parts: one of which is written before the CGH in the field of future hologram and the second one is written during the long-term writing of the CGH. The shift between the first and second part of the microstructure is the trace of the writing errors and allows one to determine and calculate the error of CGH fabrication along both orthogonal coordinates.

Towards reliable diagnostics of prostate cancer via breath.

Early detection of cancer is a key ingredient for saving many lives. Unfortunately, cancers of the urogenital system are difficult to detect at early stage. The existing noninvasive diagnostics of prostate cancer (PCa) suffer from low accuracy (< 70%) even at advanced stages.

The role of gold nanoparticles' aspect ratio in plasmon-enhanced luminescence and the singlet oxygen generation rate of Mo clusters.

Here we present a study on the effect of the aspect ratio (AR) of gold nanoparticles on the emission intensity and singlet oxygen production rate of hexamolybdenum cluster-doped silica particles. It was shown that these parameters can be enhanced gradually up to 6.7- and 13-fold with the AR.

Monitoring the Reaction of the Body State to Antibiotic Treatment against via Infrared Spectroscopy: A Case Study.

The current understanding of deviations of human microbiota caused by antibiotic treatment is poor. In an attempt to improve it, a proof-of-principle spectroscopic study of the breath of one volunteer affected by a course of antibiotics for eradication was performed. Fourier transform spectroscopy enabled searching for the absorption spectral structures sensitive to the treatment in the entire mid-infrared region.

Solitons in a Box-Shaped Wave Field with Noise: Perturbation Theory and Statistics.

We investigate the fundamental problem of the nonlinear wave field scattering data corrections in response to a perturbation of initial condition using inverse scattering transform theory. We present a complete theoretical linear perturbation framework to evaluate first-order corrections of the full set of the scattering data within the integrable one-dimensional focusing nonlinear Schrödinger equation (NLSE). The general scattering data portrait reveals nonlinear coherent structures-solitons-playing the key role in the wave field evolution.

Dipole ordering of water molecules in cordierite: Monte Carlo simulations.

Electric dipoles of water molecules, enclosed singly in regularly spaced nanopores of a cordierite crystal, become ordered at low temperature due to their mutual interaction and show the frequency dependence of their dielectric susceptibility, typical for relaxor ferroelectrics, according to recent experimental data. The corresponding phase transition is accompanied by anomalies in thermodynamic quantities, such as heat capacity and dielectric susceptibility, which are calculated here using the Monte Carlo method, and their agreement with the experimental data is discussed. Despite the increase in the correlation length, the partially filled dipole lattice at low temperatures, according to the calculations, does not have long-range order and corresponds to a dipole glass.

Theory helps experiment to reveal VOCs in human breath.

Volatile organic compounds (VOCs) present in human breath not only provide information about the internal chemistry of the body but can also be specific to diseases. Therefore, detection and analysis of specific VOCs can be used for medical diagnostics. However, up until today in spite of several existing VOC-based detection techniques and significant efforts, breath analysis is not a diagnostic method available for clinicians.

Nonlinear Spectral Synthesis of Soliton Gas in Deep-Water Surface Gravity Waves.

Soliton gases represent large random soliton ensembles in physical systems that exhibit integrable dynamics at the leading order. Despite significant theoretical developments and observational evidence of ubiquity of soliton gases in fluids and optical media, their controlled experimental realization has been missing. We report a controlled synthesis of a dense soliton gas in deep-water surface gravity waves using the tools of nonlinear spectral theory [inverse scattering transform (IST)] for the one-dimensional focusing nonlinear Schrödinger equation.

Closed-Loop Temperature Control Based on Fiber Bragg Grating Sensors for Laser Ablation of Hepatic Tissue.

Laser ablation (LA) of cancer is a minimally invasive technique based on targeted heat release. Controlling tissue temperature during LA is crucial to achieve the desired therapeutic effect in the organs while preserving the healthy tissue around. Here, we report the design and implementation of a real-time monitoring system performing closed-loop temperature control, based on fiber Bragg grating (FBG) spatial measurements.

Synergetic Effect of Mo Clusters and Gold Nanoparticles on the Photophysical Properties of Both Components.

Photodynamic and photothermal therapies (PDT, and PTT, respectively) are promising candidates for multimodal anticancer therapies (i.e., combinations of therapies), since their action is based on mechanisms that generally cannot be resisted by cancer cells, that is, generation of highly oxidizing oxygen species and high temperature, respectively.

Dielectric ordering of water molecules arranged in a dipolar lattice.

Intermolecular hydrogen bonds impede long-range (anti-)ferroelectric order of water. We confine HO molecules in nanosized cages formed by ions of a dielectric crystal. Arranging them in channels at a distance of ~5 Å with an interchannel separation of ~10 Å prevents the formation of hydrogen networks while electric dipole-dipole interactions remain effective.

Anomalous errors of direct scattering transform.

Theory of direct scattering transform for nonlinear wave fields containing solitons is revisited to overcome fundamental difficulties hindering its stable numerical implementation. With the focusing one-dimensional nonlinear Schrödinger equation serving as a model, we study a crucial fundamental property of the scattering problem for multisoliton potentials demonstrating that in many cases phase and space position parameters of solitons cannot be identified with standard machine precision arithmetics making solitons in some sense "uncatchable." Using the dressing method we find the landscape of soliton scattering coefficients in the plane of the complex spectral parameter for multisoliton wave fields truncated within a finite domain, allowing us to capture the nature of such anomalous numerical errors.