Journal of Russian Laser Research最新文献

We successfully demonstrate the generation of nanosecond pulses in a passively Erbium-doped fiber laser (EDFL) by an Ag₂S-based saturable absorbeer (SA). A simple and low-cost liquid phase exfoliation (LPE) method is used to fabricate the SA. Through LPE, the SA element is coated onto a thin film of polyvinyl alcohol (PVA), which serves as the host material. The Ag₂S SA film exhibits good nonlinear absorption characteristics to give it strong potential as an ideal SA. It has a modulation depth of 25.3% and a saturation intensity of 1.11 MW/cm². The laser is able to generate a self-started mode-locked pulse at a threshold pump power of 145.83 mW with a fundamental repetition rate of 0.98 MHz and a pulse duration of 256 ns, respectively. At the maximum pump power, the laser delivers a pulse energy of 2.08 nJ and an output power of 2.11 mW. This demonstration suggests that Ag₂S SA has good capacity for generating nanosecond mode-locked lasers in the C-band region.

Optical domain–wall (DW) solitons have attracted considerable attention for their special applications in wavelength-division multiplexing and signal processing in optical communications. In this study, we construct a dispersion-managed fiber laser with a composite filtering effect composed of nonlinear polarization rotation (NPR) filtering and Lyot filtering for achieving dual-wavelength domain–wall dark–bright pulses. Our optical-domain dark–bright pulse is characterized by even, though it has two optical wavelength components, still has the same repetition frequency. The phenomenon of dual-wavelength dark and bright pulses occurs by adjusting the composite filtering, and the dark and bright pulses can be separated by continuing the filtering. Our work presents a novel approach to achieve dual-wavelength domain–wall dark–bright pulses.

In order to meet the visual characteristics of human eyes, in this paper, we propose a ghost imaging method based on binocular vision matching fusion. The imaging process of the left-eye camera and the right-eye camera in binocular vision system is realized, using ghost imaging algorithm, and its weak signal imaging characteristics can effectively compensate the parallax between the left-eye camera and the right-eye camera. The Speeded Up Robust Features algorithm is used to match the feature points of the two sub-images. Combined with the fusion algorithm of New Sum of Modified Laplacian, the two sub-images after registration are fused to obtain a clearer image. Whether from the visual perception (human vision) or objective analysis (CC, SSIM, IE, RMSE, PSNR, and BER), it can be proved that the proposed scheme has better image quality, better fidelity and robustness, and is closer to the ideal image, which provides a new method for binocular vision imaging technology.

We study the graphene (Gr)-strengthened CoCrFeNiMo_0.2 high-entropy alloys (HEAs) prepared by laser cladding. The corrosion properties of the alloys under simulated acid rain conditions are studied through rainfall experiments, electrochemical experiments, and immersion experiments. The experimental results show that the microstructure of the Gr-strengthened CoCrFeNiMo_0.2 HEAs mainly including three morphologies. Mo element occurs segregation. Gr concentrates on the alloy surface during melting. The alloy has a face centered cubic (FCC) single-phase structure. With increase in the rainfall and immersion period, the corrosion resistance of the Gr-strengthened HEAs decreases. With increase in the pH, the corrosion resistance of the alloys increase. The corrosion current densities of Gr-strengthened CoCrFeNiMo_0.2 HEAs are small, indicating that the alloys have excellent corrosion resistance. Electrochemical impedance spectroscopy (EIS) shows that as the pH increases, the capacitance arc radius, impedance modulus, and phase angle show increasing trend. The reason for excellent corrosion resistance are as follows: the Gr enriched on the surface plays a shielding role during alloy melting, Gr reacts with alloy elements to form a passive film on the alloy surface, the lattice distortion and grain refinement are caused by Gr, providing the single-phase structure of the alloy.

Many devices based on silicon and other photonic integrated circuit platforms exhibit significant polarization dependence. Polarization beam splitter (PBS) is a device that split optical signals into transverse electric (TE) and transverse magnetic (TM) modes. Among various PBSs, asymmetric directional couplers are widely used due to their fine performance, but their working bandwidth is limited due to wavelength changes that can lead to deviations in effective refractive index and coupling strength. We propose a PBS, which uses metamaterial anisotropy to replace structural asymmetry and break the bandwidth bottleneck. It achieves good performance in the wavelength range of 258 nm, where the extinction ratio of the TM polarization is greater than 24 dB and that of the TE polarization is greater than 26 dB. It covers the E, S, C, L, and U bands, and the coupling area is as small as 7.25×2.625 μm, with a total device footprint of 15.65×6.125 μm.

We present the results of our study of nonlinear optical response observed in plasmon–exciton nanostructures based on PbS quantum dots passivated with thioglycolic acid and gold nanorods under the influence of 10 ns second harmonic pulses (532 nm) of Nd³⁺:YAG laser. We show that the association of components of a hybrid nanostructure leads to increase in the reverse saturable absorption in PbS quantum dots against the background of nonlinear refraction. Coating quantum dots with a monolayer of SiO₂ reduces this effect due to blocking the process of phototransfer of charge from a quantum dot to a metal nanoparticle, which is confirmed by the quenching and reduction in the luminescence lifetime of PbS quantum dots in the presence of gold nanorods.

Rydberg atom has a very large polarizability proportional to n⁷ (n is the principal quantum number), the energy interval between adjacent energy levels is in the microwave frequency band, and the transition between adjacent energy levels has a huge dipole moment proportional to n⁴; as a result, the Rydberg atom is extremely sensitive to the external field, making it an important means of microwave detection. The interaction of Rydberg atoms with laser fields can be described within the framework of density matrix theory. In this paper, based on a four-level system with multiple laser fields, we study the relationship between the population distribution of different energy levels and the detuning of the coupling field, as well as the effect of the Rabi frequency of microwave field on the electromagnetically induced transparency (EIT) signal by solving the density matrix of the steady state system. Considering the characteristics of density matrix, we assume that the diagonal elements are real and the off-diagonal elements are complex. We find that the operation efficiency of this construction method is twice as high as that of the direct representation by complex numbers. At the same time, we obtain that the Rabi frequency of microwave electric field is proportional to the splitting of EIT signal within a certain range.

We asses impact of the temperature of ⁸⁷Rb atoms on the linewidths and amplitudes of the F = 1 → F′ = 0, 1, 2 and F = 2 → F′ = 1, 2, 3 hyperfine resonances of the ⁸⁷Rb D₂ line, using the circularly-polarized pumping beam and the probe laser beam. To achieve high-precision and accuracy, frequency-stabilized narrow-linewidth extended-cavity diode lasers, we employ a temperature-controlled Fabry–Pérot interferometer and a magnetically-shielded temperature-controlled Rb cell with dimensions in the centimeter range, containing enriched ⁸⁷Rb atoms. Consequently, the linewidth and amplitude measurements are conducted with inaccuracies of 1.5 MHz and 0.4 mV, respectively.

We investigate effects of a classical external field and the initial state of the field on the nonlinear interaction of a Λ-type three-level atom with the two-mode field through the Raman type interaction. Appropriate canonical transforms are performed for atomic states. The analytic solution to the model is obtained, using the Schrödinger differential equation. The wave function is obtained under specific initial conditions of the atom and field. The effect of a classical external field and the initial state of the field on the population occupations, the squeezing phenomenon, and the atomic emission spectrum are studied. The collapse–revival phenomena are affected by the presence of the classical field. Increasing the activation of the role of the initial state of the field improves the phenomena of collapses and revivals. The squeezing intervals decrease with increase in the classical field effect. The squeezing intervals increase with decrease of the parameter of the initial state of the field. The maximum values of the emission spectrum are improved after taking into account the classical field. In addition, the peaks significantly decrease after reducing the influence of both the bandwidth of the filter and the interaction time.

For CdZnTe crystals containing extended defects – coherent and incoherent twin boundaries, as well as lamellar systems of twins, we measure the propagation patterns of surface acoustic waves (SAW) in the gigahertz range excited by a sharply focused femtosecond laser pulse. Comparison of the calculated SAW radial velocities with experimental data allows us to determine the local crystallographic orientation of crystal regions with defects. We discover strong anisotropic scattering of SAW at twin boundaries and show that the structure of the twin boundary can be determined from the pattern of SAW scattering. Also, we demonstrate the non-reciprocal SAW propagation in lamellar twin systems, as well as quasi-waveguide SAW propagation along the lamellar twin layer.