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In this article, we studied high-energy single frequency transform-limited Er-doped amplifiers core pumped by a specially developed Yb-doped fiber laser at 980 nm and a Raman laser at 1480 nm. It was demonstrated that pumping at 1480 nm allows achieving slightly higher maximum pulse energy for long pulses in the absence of nonlinear effects. At the same time, amplifiers with a pump at 980 nm have a higher threshold of stimulated Brillouin scattering (SBS), and higher peak power of shorter pulses can be achieved in such a scheme. Lasers with more than 730 μJ pulse energy and with higher than 3.5 kW peak power were demonstrated.

Silica-based optical fibers with an ultra-high Yb concentration were systematically studied. Three the most commonly used in industry glass matrixes for active fiber core were investigated: aluminosilicate, phosphosilicate and aluminophosphosilicate. For all the glass hosts optical fibers doped with a record high concentration of Yb in a glass core were fabricated utilizing an all-gas-phase deposition based on MCVD technology. The factors limiting increase of Yb content in glasses and fibers were revealed. For the first time it was shown that highly Yb-doped fibers could nearly completely lose their active properties and the most probable reason for that is concentration quenching of luminescence.

VT transition from the high-spin CoIIto low-spin CoIIIstate was observed for complex (N-cyclo-hexyl-2-iminopyridine)(3,6-di-tert-butyl-o-benzosemiquinonato)(3,6-di-tert-butyl-catecholato)cobalt in both solid and liquid form. For the first time we demonstrate a low-temperature nanosecond pump-probe XANES experiment revealing the valence tautomeric transition in a solution of Co complex. Reversible transition was induced both under the temperature and laser radiation stimuli.We assembled a flow-through cooling system and measured pump-probe nanosecond K-edge X-ray absorption near-edge structure to observe excited-state relaxation dynamics of valence tautomeric complex (N-cyclo-hexyl-2-iminopyridine)(3,6-di-tert-butyl-o-benzosemiquinonato)(3,6-di-tert-butyl-catecholato)cobalt. Obtained results showed that for this complex reversible transition can be induced both under the influence of temperatures and laser radiation.

Abstract: A representative of the family Apiacea, Sosnowsky’s hogweed (Heracleum sosnowskyiManden.), previously cultivated as a fodder plant and now occupying vast territories along roads and railways, in and near settlements, uncultivated agricultural lands, on farms and in many other areas poses a serious threat to human health. On these lands, an active eradication campaign has been going on for over 15 years. This invasive species also spreads actively on the lands of the forest fund including plantations, felling sites, young stands of natural origin, clearings and hayfields, forest stands of different ages with a small basal area, and in the most productive forest conditions. As a result, in forest plantations growth of woody plants (primarily of coniferous species) is inhibited, their death is observed, and environmental, aesthetic and industrial damage increases due to the growth and dominance of Sosnowsky’s hogweed. As a result of field experiments in the Leningrad region, a high effectiveness of a number of modern herbicides (Roundup, Anchor-85, and Magnum) for control of Sosnowsky’s hogweed and other unwanted herbaceous vegetation, as well as their selectivity in relation to pine and spruce, has been demonstrated.

Misfires and fuel shutdown have similar features and affect similarly on overheating the three-way catalyst (TWC). In practice, this similarity is an obstacle to determining whether the misfires or fuel shutdown cause failure of the TWC. Meanwhile, it is of great importance to distinguish fuel shutdown as an original reason from others because its consequences may be tremendous for both the environment and safety. The destruction mechanism of the TWC resulting from the shutdown of fuel supply is described in detail. The mechanism is confirmed by the experimental data obtained on a four-cylinder in-line engine tested on motor bench. The burning process is transferred from the cylinders into the TWC during the fuel shutdown event. The entire process is divided into several stages. Initially, the air-fuel mixture in the cylinders changes so that the air/fuel ratio increases, reaching the lean misfire limit and going beyond this limit, which makes the air-fuel mixture non-combustible. The remains of fuel and oxygen unreacted in the cylinders enter the TWC where combustion occurs in a combination of the catalytic mode, flame combustion in the porous medium and free flame. The destruction mechanism of the TWC due to the fuel shutdown is a sequence of rapid changes in combustion modes in the engine and in the TWC. It may seem strange, since the expected consequence should be a decrease in temperature, as the amount of fuel supplied is reduced. Contrary to the expectations, the fuel shutdown leads to an abrupt heating of the TWC and its complete destruction in an extreme case.

We investigate (both theoretically and experimentally) a method for fundamental mode spectral filtering in single-mode optical fibers using the resonant mode coupling effect. We demonstrate the possibility of controlling the spectral bandwidth of the fundamental mode suppression band through appropriate choice of fiber parameters and fiber bending. The developed technique can be very useful for the design of fiber-based spectral filters (i.e., active fibers with suppression of laser emission at undesirable wavelengths, suppression of stimulated Raman scattering).

To raise the stimulated Brillouin scattering (SBS) threshold, we have fabricated an optical fibre having a core heavily doped with germanium oxide and displaced from the fibre axis. A method has been proposed for broadening the SBS gain spectrum of the fibre by winding it onto a small-diameter spool, and a broadening of the spectrum by 5.4 dB has been demonstrated, which indicates an increase in SBS threshold by 4.1 dB.

The feasibility of making a wavelength-selective fibre filter using fibre with absorbing rods in its silica cladding has been demonstrated theoretically for the first time. The technique described in this paper is of great practical interest for designing fibre lasers and amplifiers emitting at wavelengths where lasing is impeded by the presence of more energetically favourable radiative transitions in the active medium. In addition, the approach proposed here can be used for stimulated Raman scattering suppression. The unique feature of the fundamental core mode suppression mechanism examined is that there is a (bending) controlled spectral width of a region where excess losses are produced.

In this paper, we present a novel single-mode Yb-doped fiber with 14 µm core and 45 µm cladding diameter. A 976 nm all-fiber high-power amplifier was manufactured based on this fiber. 10-mm-long fiber taper was used to launch the pump light, and guidance of the high NA pump was provided by a glass–air interface. 13 W output power limited only by the available pump power was achieved with 31% slope efficiency.

Especially grown crystals (elongated plates) of the complex (1,10-phen)Co(3,6-DBSQ)2(1) reversibly elastically bend under laser excitation (532 or 808 nm) and/or heating in the temperature interval ∼242–265 K (1,10-phen = 1,10-phenanthroline, 3,6-DBSQ = anion-radical and 3,6-DBCat = dianion of 3,6-di-tert-butyl-o-benzoquinone). The abrupt interconversion of valence tautomers is observed in this temperature range: (phen)Co(3,6-DBCat)(3,6-DBSQ) ⇌ (phen)Co(3,6-DBSQ)2. Solving the problem of design of photo- (thermo-) actuators with preset parameters, the series of solid solutions of general formula (phen)x(bpy)1–xCo(3,6-DBSQ)2was obtained and crystallized as thin elongated plates. Crystals of each solid solution demonstrate the maximal photomechanical response (bending) at a temperature close to its own valence tautomeric (VT) transition temperature. On the other hand, the VT transition temperature depends on the composition of the solid solution. So, by setting the composition of the solid solution, one can set the temperature of the photomechanical response. It is the first example of temperature-manageable photomechanical properties.

In this Letter, we propose and realize a novel concept for a high-peak-power highly efficient fiber amplifier in the 1.55 µm spectral range. The amplifier is based on the simultaneous utilization of Er-doped, Yb-free, and Er-Yb codoped large-mode-area fibers spliced together. Using this approach, we demonstrate the amplification of single-frequency 160 ns pulses at 1554 nm to a peak power of 3.7 kW with a pump-to-signal conversion efficiency of 23.6% relative to the launched multimode pump power at 976 nm.

Abstract: The photoexcitation energy transfer in donor–acceptor (DA) systems formed from a mixture of semiconductor polymer poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with fullerene C60and endohedral metallofullerene Ho@C82have been investigated. It is established that the migration of excitons between polymer segments significantly affect the quenching of MEH-PPV luminescence. The Forster radii of nonradiative energy transfer are estimated for the DA systems under study. It is shown that the DA system formed using endohedral metallofullerenes is most efficient. Model photovoltaic cells with different C60and Ho@C82doping levels are formed based on MEH-PPV. The spectral sensitivity of photovoltage and kinetics of rise in the photovoltage signal under pulsed irradiation are measured for the formed cells. The charge carrier mobility in the polymer composites under study is estimated. It is established that a change in the endohedral metallofullerene concentration within 1–2% makes it possible to change the effective free-carrier mobility of the polymer heterojunction.

We consider a fibre laser system generating [?]10-uJ, [?]500-fs pulses with a peak power of [?]10 MW at a repetition rate of 100 kHz and emission wavelength of 1.56 um. The system is based on a master oscillator - power amplifier configuration. The amplifier ensures chirped-pulse amplification. The pulses are then compressed by a dispersive grating compressor. The output amplifier stage is based on a specially designed tapered large mode area erbium-doped fibre for suppressing nonlinear effects. The experimental data agree with numerical simulation results for the stretcher, amplifier and compressor. The stretcher and amplifier have been simulated using a generalised nonlinear Schrodinger equation. In addition, numerical simulation results suggest that optimising the stretcher and compressor will potentially allow the peak power of the system to be scaled up to [?]30 MW.

The purpose of this study is to understand the political, social, economic and military factors that shaped the evolution of Spanish shipbuilding for the Acapulco-Manila trade route under the Habsburg and Bourbon dynasties (1571–1815). It focuses on the main variables that affected the size of the trans-Pacific galleons, on the objectives of the Spanish crown’s shipbuilding legislation, and on the methods used by Spanish colonial administrators to mobilize human and material resources in the Philippines. It discusses the role of the religious orders in the functioning of this industry, particularly in opposing the negative social consequences of shipbuilding. It also details the administrative reforms that shaped the development of this industry during the eighteenth century, which sought to limit the exploitation of the local workforce by transferring executive powers from local government officials and encomenderosto the friars. Finally, it also discusses the measures implemented by the Bourbon regime to increase its control over the functioning of the shipyards, particularly during the late eighteenth century. Although this article focuses on the construction of the largest ships launched from the Philippine shipyards, its conclusions can be extended to other types of vessels built by the Spanish administration in the archipelago during this period.

Abstract—The changes in the microstructure during thermomechanical treatment under different regimes of a new granulated heat-resistant alloy based on VZh178P nickel obtained by the method of hot isostatic pressing and subsequent hot deformation (HIP + deformation) are studied. The change in the grain size of the γ matrix after the main operations of the technological conversion is shown; the dynamics of their growth in hardening below and above the temperature of total dissolution of the γ' phase and the microstructure after the total thermal treatment are shown.

New opportunities due to the advancements in the techniques and methods of broadband resonator spectroscopy in the millimeter and submillimeter range (also known as the terahertz region) are considered in this paper. An upgraded variant of the spectrometer produced at the Institute of Applied Physics, Russian Academy of Sciences (Nizhny Novgorod, Russia) possessing a sensitivity to the absorption coefficient of approximately 4 × 10−9 cm−1 is presented. The spectrometer allows the continuous recording of gas spectra in the 45–500 GHz frequency range (six waveguide subbands) at pressures of 10–1000 torr. A fully automated spectrum recording within the waveguide subband reduces the overall time required for the experiment by almost an order of magnitude. Examples of recording the spectra of oxygen and water vapor resonance lines, as well as of continuum absorption, including the rotationally resolved water dimer spectrum, are presented. It is demonstrated that the uncertainty of measuring the broadening parameter of diagnostic atmospheric lines may be reduced to 0.1%, which meets the stringent present-day requirements of remote sensing of the atmosphere. The physically attainable ultimate sensitivity of broadband microwave resonator spectrometers of various types is discussed. Prospects for further development of the spectrometer and its application for solving fundamental and applied problems of spectroscopy are analyzed.

We have studied absorption spectra of optical fibres doped with rare-earth ions (Sm3+, Tm3+, Tb3+, Pr3+ and Ho3+) and demonstrated that they are potentially attractive for ensuring wavelength-selective absorption in fibre lasers. Such fibres can be used for pump diode protection against back-reflected light at the operating wavelength of neodymium, erbium, erbium - ytterbium or thulium lasers. A proper choice of a rare-earth element makes it possible to ensure a strong absorption (10-20 dB) at the operating laser wavelength in combination with high transmission (loss under a few tenths of a decibel) at pump wavelengths. To demonstrate the potential of the proposed approach, we have fabricated and investigated Tm3+-doped fibre compatible with the output fibre pigtails of standard semiconductor diodes used for pumping (core diameter, 105 um; numerical aperture, 0.22). We have demonstrated the possibility of effectively suppressing light in the 1550-nm range by more than 20 dB even in the case of a high-power (up to 10 W) undesirable signal. Under such conditions, the total pump loss does not exceed 0.5 dB and can be further reduced by optimising the core composition and fibre design.

Iminopyridine modified by TEMPO nitroxide was utilized for the synthesis of an octahedral bis(o-semiquinonato)cobalt complex. Variable-temperature magnetic susceptibility measurements detect a valence tautomeric transformation in the temperature range 200–300 K. A reproducible hysteresis loop of about 40 K width is observed on the magnetic moment temperature dependence in the transition region. Differential scanning calorimetry measurements confirm different temperatures of phase transitions accompanying a valence–tautomeric transformation upon heating and cooling. Attempts to study the structural changes associated with the valence–tautomeric transformation by single-crystal X-ray diffraction failed because of the crystal destruction taking place upon cooling from 220 K. The powder X-ray diffraction pattern indicated an essential change of the unit cell upon cooling from 240 K.

An improved MCVD process has been proposed which allows one to fabricate ytterbium-doped fibre preforms with a fluorine-doped aluminosilicate glass-based core. Using this process, we have demonstrated the possibility of codoping the glass with high Yb3+ concentration (about 2 wt %), high fluorine concentration (2 wt %) and aluminium oxide concentration above 1.5 mol % (to ensure high ytterbium solubility), resulting in a record low refractive index of the glass (Dn [?] 0.000 - 0.003). A series of fibre with a SiO2 - Al2O3 - GeO2 - Yb2O3 - F core have been fabricated and their optical characteristics have been investigated. In particular, we have demonstrated the possibility of reaching the highest possible lasing efficiency (82.7 % with respect to absorbed pump power). We have studied the photodarkening level in the fibres as a function of ytterbium concentration and demonstrated the feasibility of making ytterbium-doped fibre amplifiers based on the described fibres, with an extremely low output power degradation rate (less than 20 % after 10 000 h of continuous operation).