Bright Soliton and Bright–Dark Soliton Pair in an Er-Doped Fiber Laser Mode-Locked Based on In2Se3 Saturable Absorber

The output power in ultrafast fiber lasers is usually limited due to the lack of a versatile saturable absorber with high damage threshold and large modulation depth. Here we proposed a more efficient strategy to improve the output energy of erbium-doped fiber laser based on indium selenide (In2Se3) prepared by using the physical vapor deposition (PVD) method. Finally, stable mode-locked bright pulses and triple-wavelength dark–bright pulse pair generation were obtained successfully by adjusting the polarization state. The average output power and pulse energy were 172.4 mW/101 nJ and 171.3 mW/100 nJ, which are significantly improved compared with the previous work. These data demonstrate that the PVD-In2Se3 can be a feasible nonlinear photonic material for high-power fiber lasers, which will pave a fresh avenue for the high-power fiber laser.

2 μm passively mode-locked thulium-doped fiber lasers with Ta2AlC-deposited tapered and side-polished fibers

In this work, mode-locked thulium-doped fiber lasers operating in the 2 µm wavelength region were demonstrated using tantalum aluminum carbide (Ta2AlC)-based saturable absorbers (SAs) utilizing the evanescent wave interaction. The Ta2AlC MAX Phase was prepared by dissolving the Ta2AlC powder in isopropyl alcohol and then deposited onto three different evanescent field-based devices, which were the tapered fiber, side-polished fiber, and arc-shaped fiber. Flame-brushing and wheel-polishing techniques were used to fabricate the tapered and arc-shaped fibers, respectively, while the side-polished fiber was purchased commercially. All three SA devices generated stable mode-locked pulses at center wavelengths of 1937, 1931, and 1929 nm for the tapered, side-polished, and arc-shaped fibers. The frequency of the mode-locked pulses was 10.73 MHz for the tapered fiber, 9.58 MHz for the side-polished fiber, and 10.16 MHz for the arc-shaped fiber. The measured pulse widths were 1.678, 1.734, and 1.817 ps for each of the three SA devices. The long-term stability of the mode-locked lasers was tested for each configuration over a 2-h duration. The lasers also showed little to no fluctuations in the center wavelengths and the peak optical intensities, demonstrating a reliable, ultrafast laser system.

Generation of stable mode-locked fiber laser based MWCNTs in 1.5-µm waveband

Pulses fiber laser had been successfully generated by using multi-wall carbon nanotubes thin film saturable absorber at room temperature. The saturable absorber is incorporated into a ring laser cavity. A stable Kelly sidebands mode-locked pulse spectrum with 1561.3 nm wavelength at the pump power of 86.8 mW. The repetition rate and pulse width of 12.3 MHz and 0.51 picosecond, respectively. A stable operation is observed for an hour at room temperature. These simple and reliable system features offer interesting research study especially in mode-locked pulse generation at 1.5 μm waveband.

The generation of nanosecond pulses at C-band region with titanium dioxide as a saturable absorber

A passive mode-locked in an erbium-doped fiber laser with titanium dioxide (TiO2) film as a saturable absorber (SA) has been successfully demonstrated. The film is fabricated using a liquid phase exfoliation, which offers a simple and low-cost method. The self-starting mode-locked was created by inserting a 200-meter-long single-mode fiber into the laser cavity to balance the nonlinearity and dispersion of the cavity. The pulses operate stably at a central wavelength of 1560 nm. The pulse repetition rate was almost fixed at 988 kHz at a tuneable pump power from 145.83 mW to 187.04 mW. The repetition rate shows excellent stability with a signal-to-noise ratio (SNR) of 69 dB whilst the pulse width was virtually constant at 230 ns. The maximum output power was measured at 2.17 mW, eliciting maximum pulse energy of 2.19 nJ. This experiment demonstrates that stable mode-locked pulsed can be generated using TiO2-SA.

Flow Behaviour Assessment of Smokey SAM Rocket Prototype

This paper presents an aerodynamic assessment on the "Smokey Sam Prototype (TRL-6) Start (X)". Initially, the rocket prototype was designed using OpenRocket open source software, where all of the user's design requirements and objectives are considered. The TRL-6 Smokey Sam Star (X) is expected to fly within 400 m with the operating Mach 0.2, as comparable to US GTR-18A. This research evaluates the aerodynamics performance of the design Smokey Sam prototype rocket using a computational fluid dynamics (CFD) approach. For instance, the CFD study assessed the flight performance and stability once launched, such as lift coefficient, drag coefficient and pitching moment. This research employs K-omega (k-ω) model to express the turbulent properties of the flow. The actual pressure distribution was compared with the conventional rocket material's exact pressure distribution to inspect the best rocket material to sustain the best strength to weight ratio at high-speed trajectory operation. Several observations were made into the modelling process, such as surrounding velocity and pressure. It is found that the flight is in stable mode since the obtained pitching moments are almost zero at all assessed speeds.

Analyzing mechanics of rock breaking under conditions of hydromechanical drilling

Purpose is to substantiate design factors and technological parameters of next-generation facilities of hydromechanical drilling basing upon the determined features of interaction between breaking pellets and rock mass. Methods. The studies of directionality features and bottomhole processes for rock mass breaking have been carried out using the current analytical methods and laboratory experiments. Among other things, certain mathematical and physical simulation techniques, methods of theoretical processing and interpretation of the research results under SolidWorks, Statgraphics, and Маthсаd environments, and a number of relevant instruments and materials have been applied. Following their technological sequence, the well bottomhole rock-breaking processes were simulated using a special laboratory stand equipped with a control-and-measuring unit (inclusive of a flowmeter, manometer, tachometer, and coordinate spacer among other things). Findings. Application perspectiveness of the combined techniques for rock breaking has been proved. Structural designs of the next-generation facilities for well drilling have been proposed. The pellet-impact drilling features have been analyzed from the viewpoint of its significant dynamic component during the rock mass breaking. Nature of the effect of breaking load rate on the results of bottomhole deformation processes has been identified. Efficiency of the proposed scheme to improve pellet-impact drilling based upon maximum use of a well bottomhole deformed by pellets has been proved. Measures to increase technical and technological indicators of pellet drilling have been considered. Requirements for the conditions stabilizing operation of a collar of the pellet-impact device have been outlined. Further research tendencies have been specified. Originality. It has been determined that compliance with specific geometrical and hydromechanical ratios, corresponding to the stable mode of a well sinking, is the factor required for reliable operation of hydromechanical drilling facilities. Practical implications. The results of stand-based tests as well as analytical studies may become the foundations to develop efficient engineering decision for hydromechanical well drilling with high technical and economic indicators. The data, concerning bottomhole rock breaking processes, are the basic ones to work out rational standard parameters of well sinking processes.

CENTRIFUGAL COMPRESSOR PERFORMANCE MAPS TREATMENT FOR INTERNAL COMBUSTION ENGINES OPERATING CYCLE SIMULATION

Simulation of the supercharged internal combustion engines operation cycle is impossible without correct estimation of the supercharger operating parameters. Standard approach is to use specially prepared performance maps of compressor and turbine of the turbocharger, which are based on the experimental (or manufacturer’s) raw data. Centrifugal compressor performance maps interpolation, extrapolation and treatment provides challenging requirements as it is important to get correct simulation under such special conditions as compressor choke, rotating stall and pumping surge. At the same time it’s important to obtain the fast and stable calculations of the engine’s operating cycle. Blitz-PRO – online internal combustion engines operating cycle simulation service – offers supercharger performance maps preprocessing and implementation. It provides three different modes of compressor surge consideration during calculations: 1) full-scale surge mode using Moore-Greitzer approach; 2) mild surge mode with flexible adjustment; 3) “stable” mode, when the surge is neglected and the compressor constant-speed lines are extended from the rotating stall point to the lower mass flow region with the hyperbolic equation. Using the MAN 8G70ME-E engine 12140 kW, 82 rpm operating point as an example, the calculation results are compared for three modes of compressor surge consideration. The “stable” mode provides the fastest and the most stable calculations, while the calculations under the full-scale surge mode could generate the numerical (nonphysical) instability of calculations, which are caused by the high sensitivity of the two-stroke engines to the gas exchange processes as it is shown. The mild surge mode provides fast and stable enough calculation with the surge consideration ability, which could be assumed as the best solution for the given example. The researcher should choose between provided three modes of the centrifugal compressor surge consideration according to the calculations tasks, preferring “stable” mode for initial model setup and mild surge mode for the surge probability check, while the accurate compressor surge simulation needs further development.

Convective instability of air flows in the exhaust shaft above a four-row finned beam

Herein, multidirectional quasiperiodic air flows in an exhaust shaft above a four-order horizontal bundle consisting of bimetallic finned tubes used to remove heat in heat exchangers are considered. Modeling of the air movement is carried out on the basis of equations for thermogravitational convection in the Boussinesq approximation. It takes into account the viscosity of the air and the dependence of the air density on the temperature. An interpretation of quasiperiodic airstreams is proposed on the basis of Rayleigh – Bénard convection, as a result of which regular structures, called Rayleigh – Bénard cells, are formed in a liquid or gas. Rayleigh – Bénard cells are an analytical solution to the problem of the stability of hydrodynamics flows in the linear approximation. The appearance of two-dimensional (convective rolls) and threedimensional (rectangular cells) is possible. To estimate the number of emerging structures, the critical Rayleigh numbers were calculated, which characterizes the transition from an unstable mode of the convective fluid flow to a stable mode. For two experiments, the experimental Rayleigh numbers are compared with their critical values. The differences between the experimental conditions and the ideal boundary conditions used in the calculations and the partial destruction of quasiperiodic structures as a result of this are also discussed.

2 μm Passively Mode-Locked Thulium-doped Fiber Lasers with Ta2AlC-deposited Tapered, Side- polished and D-shaped Fibers

In this work, mode-locked thulium-doped fiber lasers operating in the 2 µm wavelength region were demonstrated using tantalum aluminum carbide (Ta2AlC)-based saturable absorbers (SAs) utilizing the evanescent wave interaction. The Ta2AlC MAX Phase was prepared by dissolving the Ta2AlC powder in isopropyl alcohol (IPA) and then deposited onto three different evanescent field-based devices, which were the tapered fiber, side-polished fiber (SPF), and D-shaped fiber. Flame-brushing and wheel-polishing techniques were used to fabricate the tapered and D-shaped fibers, respectively, while the side-polished fiber was purchased commercially. All three SA devices generated stable mode-locked pulses at center wavelengths of 1937, 1931, and 1929 nm for the tapered, side-polished, and D-shaped fibers. The frequency of the mode-locked pulses was 10.73 MHz for the tapered fiber, 9.58 MHz for the side-polished fiber, and 10.16 MHz for the D-shaped fiber. The measured pulse widths were 1.678, 1.734, and 1.817 ps for each of the three SA devices. The long-term stability of the mode-locked lasers was tested for each configuration over a 2-hour duration. The lasers also showed little to no fluctuations in the center wavelengths and the peak optical intensities, demonstrating a reliable, ultrafast laser system.

Passively mode locked thulium and thulium/holmium doped fiber lasers using MXene Nb2C coated microfiber

As a result of the emergence of two-dimensional (2D) materials for various opto-electronics applications, a new class of materials named MXenes have been attracting interests due to their outstanding nonlinear properties. In this work, an MXene niobium carbide (Nb2C) was proposed and demonstrated as a saturable absorber to induce mode-locking in thulium- and thulium/holmium-doped fiber lasers. The Nb2C solution was first prepared using the liquid exfoliation technique, and then deposited onto a microfiber for integration into the laser cavity. Stable mode-locking operation was observed in both laser cavities, where the center wavelengths of the laser were recorded at 1944 nm for the TDFL and 1950 nm for the THDFL. The generated pulses in the TDFL and THDFL had repetition rates of 9.35 and 11.76 MHz respectively, while their corresponding pulse widths were 1.67 and 1.34 ps. Both of the lasers were highly stable, having SNR values of more than 52 dB and showed no major fluctuations when tested for their long-term stabilities. The results demonstrate an excellent performance of the Nb2C as a saturable absorber, offering opportunities to further explore MXenes for future photonics devices.