Journal of Russian Laser Research最新文献

The energy distribution of particles in a gaseous system is well understood through the implementation of a statistical tool, namely, the Maxwell–Boltzmann distribution function in the velocity–space coordinate system. The Maxwell–Boltzmann distribution function is utilized to investigate the velocity distribution of plasma particles like electrons, assuming that their collision frequency does not depend on the velocity. However, there is a swift transition in converting the Maxwell–Boltzmann distribution function to the Druyvesteyn distribution function for the case where a collision frequency is directly proportional to the velocity. Our aim is to incorporate the frequency components to investigate the Maxwell–Boltzmann and Druyvesteyn distribution functions. Employing the equation of motion, we observe that the collisional electron velocity is equal to the equilibrium electron velocity ∼eE/m_eω multiplied by the collisional frequency over the external source frequency β = ν/ω corresponding to the externally applied electric field. We investigate the difference in the Druyvesteyn distribution function between sheath and pre-sheath regions, when a stream of electrons is traversing or effusing through the part of a pre-sheath region corresponding to the dimension of the order of mean free path. Velocity and corresponding energy distribution functions are compared for non-effusion and effusion cases in the collisional and non-collisional regimes. The Maxwell–Boltzmann and Druyvesteyn velocity and energy distributions are competitive when the collisional frequency is twice the frequency of the applied electric field.

In this paper, we present the results of an experimental study of the controlled contrast of optical properties of Germanium Telluride (GeTe) and Germanium Antimony Telluride (Ge₂Sb₂Te₅ or GST) 100 nm thin films, caused by laser-initiated reversible phase transitions from the amorphous-tocrystalline state, and vice versa. We demonstrate a high contrast in the transmissivity and reflectivity spectra in the wide wavelength range from 500 to 20,000 nm. We show that such a contrast of optical properties can be controlled in the set–reset mode, when samples of thin films are exposed to a nanosecond laser pulse at a wavelength of 532 nm, with a spatial distribution close to “top hat.” We confirm the laser-initiated changes in the thin film structures by X-ray diffraction analysis methods.

We focus our study on the quantum correlations of coupled photon pairs produced in an open atomic laser system, where quantum coherence is brought about by the superposition of a coherent atomic state and a coherent classical field. Quantum properties produced by photon–photon correlations are a long sought-after goal in quantum information science and technology, because photons combine at room temperature with high speed and long coherence times. The openness of the system under consideration allows quantum decoherence due to temperature and phase fluctuations to influence the quantum correlations generated. The competition between these quantum coherence and quantum decoherence leads to temporal quantum correlations, which we analyze using the time evolution of the density operator. Strong quantum correlations can be achieved by choosing an appropriate amplitude of the classical fields, treating temperature and phase fluctuations, and increasing the atomic injection rate over time. We also show that quantum entanglement is short-lived, quantum steering slowly decreases, but quantum discord increases with increasing heat bath temperature and atomic phase fluctuations. In this study, we explore the behavior of quantum correlations in an open atomic laser system and investigate the dynamics of entanglement, discord, and steering in this system and examine how they evolve over time.

To improve the output power of solar-pumped lasers, we propose a new configuration of solar disk laser. A rotating parabolic reflector acts as the primary concentrator with top and bottom radii of 1600 and 600 mm, respectively. The incident sunlight is reflected by the primary concentrator to the inlet of the heteromorphic compound parabolic concentrator (HCPC) and is absorbed by the gain medium after multiple reflection. The diameter, thickness, and doping concentration of the Nd :YAG disk are 20 mm, 1 mm, and 1.0 at.%, respectively. The two surfaces of the disk are cooled by heavy water. Owing to the increased surface area of the disk for receiving sunlight, solar absorption by the gain medium is greatly improved. Ray tracing shows that maximum absorbed solar power by the Nd :YAG disk can reach 446 W through optimizing the HCPC. Solving rate equations, we obtain the laser output power in the TEM₀₀ mode as high as ∼123 W, with a conversion efficiency of ∼27%. In addition, we analyze the temperature distribution of the solar-pumped Nd :YAG disk laser. The design of this solar concentrating system and the over-hundred-watts disk laser provides a new idea for further scaling the output power of solar-pumped solid-state lasers.

We examine and test in the laboratory our laser pulse remote sensing system, based on the number of cycles of a local oscillator. We calculate the range of an object, using a peak transmission power of 2 mW from a Mesa HP-pumped He–Ne laser with a pulse frequency of 3 kHz and a pulse width of 150 ns; also, we establish a correlation between the counted cycle and the laser wavelength. The results of outer range measurements with a range resolution of 45 m at a distance of 60 meters are presented. Here, photons are used for tracking and object identification, which being encoded using encoding technology, will be challenging to duplicate, and our optical radar will not be misplaced.

We present a theoretical study of the experimentally proved fact that, in perspective nonlinear materials with an absorption band in the tuning frequency range, two simultaneous three-wave processes are realized – optical parametric generation and generation of the second harmonic of an idler wave. The analysis is carried out, taking into account the depletion of the pump wave, the phase mismatch, and the losses of all interacting waves. These two three-wave processes can be phenomenologically described as an overall four-wave interaction of waves with a phase mismatch, which induces an effective third-order optical susceptibility in a nonlinear medium that exceeds the intrinsic third-order susceptibility of the medium. In the pump depletion regime, we give a more correct determination of the induced effective cubic susceptibility of a nonlinear medium and show that the effective cubic susceptibility depends on the intensities and coefficients of the nonlinear coupling of all interacting waves. Thus, by controlling the induced cubic susceptibility, it is possible to develop promising laser tunable sources through absorption bands in the UV and mid-IR spectral ranges.

We use a graphene/WS₂ heterojunction as a saturable absorber (SA) in a 2 μm wavelength Thulium-doped Yttrium Aluminum perovskite (Tm:YAP) crystal-based solid-state laser and realize effective modulation performance efficiency in passive Q-switching experiments. At a pump power of 18.80 W, the measured output power is 1.293 W, with a corresponding optical–optical conversion efficiency of 6.9%. Additionally, at a pump power of 11.50 W, we achieve a pulse time of 1.16 μs at a repetition frequency of 90.36 kHz. To the best of our knowledge, this is the first demonstration of the use of graphene/WS₂ heterojunctions as SA structures for 2 μm solid-state lasers based on Tm:YAP crystals.

We describe the experimental implementation of high-resolution soft X-ray spectrographs, which are stigmatic throughout their operating range. The optical configuration comprises a grazing-incidence plane VLS grating and a broadband normal-incidence focusing mirror with an aperiodic multilayer coating structure. The operating range is defined by the aperiodic multilayer mirror in use (Mo/Si: 12.5 – 25 nm; Mo/Be: 11 – 14 nm). The spectral resolution is determined by CCD detector resolution and is numerically equal to the product of the plate scale and the double pixel size. Vertically spaceresolved laser-produced plasma spectra of multiply charged ions are presented. The spatial resolution is equal to about 26 μm, the double pixel size. We discuss the prospect of extending high-resolution stigmatic spectral imaging below 11 nm and outline the data of numerical calculations of broadband normal-incidence mirrors based on aperiodic Ru/Sr and La/B₄C multilayer structures.

We develop an all-optical two-state Pauli X logic gate, using two-dimensional nano-photonic crystals (PhCs) based on photonic-crystal semiconductor optical amplifier switches (pc-SOA). An all-optical two-state Pauli X logic gate device is implemented by exploiting the cross-gain modulation property of pc-SOA (XGM) and the frequency encoding technique, which is constructed using a nano-structured photonic-crystal-based waveguide formed by a 2D square lattice of GaAsInP rods in the air background. The Pauli X gate is constructed within a two-input–two-output channel system. We confirm the operation of an all-optical two-state Pauli X logic gate by two sets of simulation experiments. For the simulation process, we use the finite-difference-time-domain (FDTD) and plane wave expansion (PWE) techniques. The frequency range of the band gap structure is determined in the transverse electric (TE) mode. The pc-SOA is used here for its highly-packed design, less consuming power, very high power transmission, and very good execution of the logic system. The simulation result at the output channels is also checked with the help of the cross-gain modulation (XGM) process. A two-state all-optical Pauli X gate device has a very fast response time (~1 ps), allowing for very fast optical information processing, which is helpful in the field of quantum computation. The speed of operation is on the order of 1 THz. The confinement of light is controlled and dominated by the nano-photonic crystal-based device (PhCs), and the frequency encoding technique can be exploited to improve the performance of the logic system.

The energy distribution characteristics of fast axial flow CO₂ lasers demonstrate that they are often used for cutting and welding metal materials, and it is generally believed that they are not suitable for material heat treatment. In order to expand the application range of these lasers, we prepare graphene (Gr) reinforced high entropy alloy (HEA) coatings, employing this type of laser under loworder mode conditions by adjusting processing parameters and cladding powder composition through orthogonal experiments. Then we study the effect of laser processing parameters on Gr/Al_xCoCrNiTi composite coatings. The research results indicate that the optimum process parameters are as follows: the laser power P = 3200 W, the scanning speed V = 14 mm/s, the cladding powder thickness d = 1.2 mm, and the spot diameter D = 4.0 mm. We find that, under the optimum process parameters, the Gr/Al_xCoCrNiTi laser cladding coatings exhibit typical dendrites and equiaxed grains. The microstructure refines with increase in the Al content. The Gr/AlxCoCrNiTi laser cladding coating mainly consists of the face centered cubic (FCC), body centered cubic (BCC), and M₂₃C₆. Increase in the Al content promotes the formation of the BCC structure. The microhardness of Gr/Al_xCoCrNiTi composite coatings range from 550 to 725 HV. The hardness is related to the solid solution strengthening caused by Gr and Al. With increase in the Al content, the microhardness of the coating shows a trend to increase, the wear resistance first increases and then decreases. The wear resistance is related to the BCC content and cracks in the coating. Orthogonal experiments and coating performance indicate that, by adjusting laser processing parameters and alloy composition, it is possible for fast axial flow CO₂ lasers to prepare Gr/Al_xCoCrNiTi composite coatings under low-order mode conditions, which can expand the applicability of these lasers.