Yb,Er:glass Microlaser at 1.5 μm for optical fibre sensing: Development, characterization and noise reduction

A fiber-pumped single-frequency microchip erbium laser was developed and characterized with the aim of using it in coherent Optical Time Domain Reflectometry (OTDR) measurements and sensing. The laser is pumped by a fiber-coupled 976 nm laser diode and provides 8 mW TEM00 single-frequency output power at 1.54 μm wavelength, suitable for efficient coupling to optical fibers. The amplitude and phase noise of this 200 THz oscillator were experimentally investigated and a Relative Intensity Noise (RIN) control loop was developed providing 27 dB RIN peak reduction at the relaxation oscillation frequency of 800 kHz

CONSTITUTIONAL AND INSTITUTIONAL STRUCTURAL DETERMINANTS OF POLICY RESPONSIVENESS TO PROTECT CITIZENS FROM EXISTENTIAL THREATS: COVID-19 AND BEYOND

A multitude of government forms and institutional variations have the same aims of serving their countries and citizens but vary in outcomes. What it means to best serve the citizens is, however, a matter of broad interpretation and so the disagreements persist. The ongoing COVID-19 pandemic creates new metrics for comparing government performance – the metrics of human deaths, or, alternatively and as we pursue it here, the metrics of the speed of government response in preventing human deaths through policy adoption. We argue in this essay that institutional and government systems with more authority redundancies are more likely to rapidly generate policy in response to crisis and find better policy solutions compared to centralized systems with minimal authority redundancies. This is due to a multiplicity of access points to policy making, which increase the chances of a policymaker crafting the “correct” response to crisis, which can be replicated elsewhere. Furthermore, citizens in centralized and unitary governments must rely on national policymakers to get the correct response as subnational policymakers are highly constrained compared to their counterparts in decentralized systems. As policy authority is institutionally defined, these policy authority redundancies correspond to specific institutional and constitutional forms. In this paper, we provide a mathematical/formal model where we specifically analyze the contrast in the speed of policy response between more centralized and autocratic states versus democratic federations

Optical diagnostics of selective laser melting and monitoring of single-track formation

The article presents the optical diagnostics results of the selective laser melting process of single-track production. The track defects detection (such as balling effect, powder free zone formation, sparking) was shown, as well as the visualization of the independent particles consolidation in a solid track. The metal evaporation and the formation of the melt pool specific gas dynamic conditions were considered as important physical phenomena. The velocities of the particle emission from the melt pool, the rate of their involvement, and the velocity of the gas flow were estimated. The results make it possible to evaluate the kinetics of mass transfer under selective laser melting process. The surface thermal field of the laser-irradiated zone strongly influences the material qualitative characteristics after selective laser melting. The results becomes the basis for the development of optical monitoring and diagnostic systems for laser additive manufacturing processes based on the melt pool temperature online controlling

Simulating the fuel cycle of a lead-cooled fast reactor

The development of nuclear power with fast reactors is associated with the implementation of a closed nuclear fuel cycle (CNFC). In this regard, one actual task is to simulate the stages of the fuel cycle with study of the neutron-physical characteristics of the core. The design of a reactor for operation in the closed nuclear fuel cycle mode is impossible without the using of verified and certified software packages for calculating fast reactors, capable of simulating all stages of the operation of the reactor facility and the fuel cycle. For the calculations, the FACT-BR software package was used, which has all the necessary capabilities to simulate the operation of the reactor in the closed nuclear fuel cycle mode, taking into account the stages of fuel storage and refabrication. The article presents a technique for modeling the fuel cycle, implemented for the operation of fast reactors with a lead coolant. To demonstrate methodology, a closed nuclear fuel cycle was simulated for the BREST-OD-300 and BR-1200 reactors for the design life. The article describes the scenarios in which the calculation of the burnup of reactor was carried out. In the considered scenarios, it is assumed that the unloading of fuel at the end of the micro campaign is conducted according to the maximum burnup. During the computational modeling the ranges of changes in fuel density and enrichment, reactivity margin, breeding ratio and isotopic composition of plutonium were determined

Laser beam profiling: experimental study of its influence on single-track formation by selective laser melting

In the article the experimental study of influences of laser beam profiling on the microstructure of the material obtained by selective laser melting is presented. Microstructure was researched by the example of single-track formation. For these needs the optical and video-monitoring stand was constructed. The defects of single-track formation were obtained by microscopy and video monitoring. The technological gaps for each laser beam profile give the possibility to use higher power for laser systems in the future with the purpose to improve productivity of SLM processing

Runways ground monitoring system by phase-sensitive optical-fiber OTDR

Runways monitoring in civil airports is typically performed by enhanced radar surveillance systems operating in the so-called Precision Runway Monitor (PRM) system that provides position of airplanes and information on their trajectories. In this paper, we propose an additional measurement system that can be used jointly with the conventional PRM approach to monitor aircrafts position on land without using the radar approach or requiring visual inspection of the lanes. We propose a system made of ground-based distributed optical fiber sensors (OFSs), to be placed below the concrete floor of the take-off and landing lanes as well as along the different roads and intersections within the airport. OFSs will be read by a phase-sensitive OTDR (Φ-OTDR) driven by low-noise narrow-linewidth 1.55 mm laser. The laser field is used to inject the optical fiber with a pulsed signal and to read the phase shifts arising from vibrations and pressure waves produced by aircrafts moving, or even still with engines turned on, along the lanes. An absolute localization of different planes, with a few meters resolution and accuracy across the whole airport, would be possible after installing OFSs and adjustment of the detection system. The proposed ground monitoring system, in addition to the ones currently available, offers information redundancy at a promising low-cost and a backup aircraft-positioning tool in case of failure or malfunctioning of the existing video-or radio-based systems. Furthermore, the proposed system is inherently immune to e.m. interference and also to intentional disturbance or intrusion. Design of the laser source and of the Φ-OTDR measurement system is underway with the aim of precise and continuous monitoring of the on-land position and movement of different aircrafts or vehicles within the airport

Fiber-Pumped Yb Er:glass Microchip Laser for Coherent OTDR Sensing

A single-frequency 1.5 um microchip erbium laser, diode-pumped through optical fiber, was developed and characterized with the aim of using it in coherent OTDR sensing applications. The laser is pumped by a fiber-coupled 976 nm laser diode and provides some 10 mW single-frequency output power at 1533.5 nm wavelength, suitable for sensing and measurements with optical fibers. Amplitude and phase noise of the 200 THz oscillator are under study for its use in specially designed OTDR measurements for remote sensing

Non-Invasive Acoustic Monitoring of Gas Turbine Units by Fiber Optic Sensors

In this article, we study the possibility of gas turbine unit (GTU) monitoring using interferometric fiber optic sensors. We used the Mach–Zehnder interferometer (MZI) scheme, which can be easily implemented and simply installed on the turbine, and also allows us to solve the problem of phase unwrapping conveniently. In this research, the following main steps were carried out: an experimental scheme based on the MZI was assembled, and its sensitive arm was fixed on the GTU under study; data on various operation modes of the GTU was collected; the data were subjected to frequency FFT analysis, based on which the main rotational speeds of the turbine were identified. With FFT analysis, we also demonstrated multiples harmonics, which appear in the case of GTU after operating time, caused by the number of blades. The possibility of GTU monitoring and analysis using a non-invasive compact fiber-optic sensor is demonstrated: spectral analysis is used to detect the rotor speed, as well as the presence or absence of high-order multiple frequencies indicating blade and bearing defects, which are determined by the number of GTU’s blades and rolling bearing used as turbines rotor supports