Journal of Russian Laser Research最新文献

We derive the analytical expressions of the average intensity of a partially coherent twisted Laguerre– Gaussian vortex (PCTLGV) beam passing through oceanic turbulence with the help of the extended Huygens–Fresnel principle. The findings show that the normalized initial profile with a dark hollow distribution of PCTLGV beam gradually converts into a flat-topped one, and finally degenerates into a Gaussian-like distribution as the propagation distance increases. The outcomes also reveal that the effect of oceanic turbulence on the propagation properties of PCTLGV beam can be effectively mitigated by regulating the twist factor and topological charge. We also find that PCTLGV beam exhibits stronger anti-turbulence ability, when the topological charge and twist factor have opposite signs as well as larger absolute values of twist factor. In addition, the PCTLGV beam will degenerate fast in stronger turbulence over the poor turbulence, which can be counteracted by increasing the initial coherence lengths. Our researches can contribute to underwater communication transmission, oceanic laser radar detection, and optical imaging.

To achieve precise removal of different coatings from carbon fiber-reinforced polymer (CFRP), we propose real-time monitoring for laser-layered paint removal. Current methods for laser paint removal on CFRP surfaces primarily focus on temperature control to safeguard the CFRP against potential damage, yet encounter challenges in providing real-time monitoring capabilities. In this study, we present laser-induced breakdown spectroscopy (LIBS) combined with partial least-squares discriminant analysis (PLS-DA) models as a promising approach. Initially, in this study, we analyze the elemental composition of carbon fiber substrates, primer, and topcoat to identify key characteristic elements for evaluating the laser-layered paint removal effectiveness. Subsequently, we explore changes in the intensities of characteristic spectral lines associated with the characteristic elements in different layers. Lastly, we develop PLS-DA models to effectively identify and classify the carbon fiber substrates, primer, and topcoat, enabling real-time monitoring of laser-layered paint removal. Based on the measured LIBS characteristic intensities and PLS-DA models, we accurately identified materials using Al I (396.164 nm) and Cr I (428.984 nm), or exclusively Cr I (428.984 nm), with 100% accuracy. The results demonstrate the feasibility of integrating LIBS with PLS-DA for monitoring laser-layered paint removal and show its potential in high-quality surface cleaning and automation.

In this study, we propose a wavelength-switchable Thulium-doped fiber laser (TDFL) based on an all-fiber Mach–Zehnder (MZ) filter. The MZ comb interferometer is designed and manufactured by welding two mismatched fiber cores. The proposed ring-cavity TDFL has a working threshold of 140 mW. Single-wavelength switchable laser emission is achieved in the range of 1841.5 to 1892.36 nm, with a minimum wavelength spacing of 3.66 nm and a side-mode suppression ratio (SMSR) of over 32.41 dB. In the experiment, four different dual-wavelength switchable and stable lasers are generated within a 44.56 nm range with 7.12 dB power shifts. Additionally, a triple-wavelength laser at 1864.77, 1888.1, and 1896.76 nm is obtained, with an SMSR of over 30.06 dB. The designed TDFL successfully achieves stable single, dual, and triple-wavelength laser emissions with power fluctuations smaller than 0.51, 1.22, and 1.32 dB, respectively.

The chemical vapor deposition (CVD) of diamond allows the controllable formation of the material with desirable structure and elemental composition. In this study, Ge-doped microcrystalline and nanocrystalline diamond (NCD) films are synthesized using microwave plasma-assisted CVD in CH₄-H₂-GeH₄-N₂ gas mixtures. We grow series of 2 μm thick NCD films with variations in gas composition [N₂] = 0 − 4% and [CH₄] = 10 − 15%. We investigate and compare the structure, phase composition, and luminescent characteristics of the grown films. The luminescent signals from Silicon vacancy (SiV, 738 nm) and Germanium vacancy (GeV, 602 nm) color centers in diamond are registered. The additional annealing of the as-grown films in air is used to remove the excessive sp² phase that hinders their luminescent properties. For both SiV and GeV centers, we find conditions for CVD growth of NCD films that are as bright or even brighter than Si-doped and Ge-doped high-quality microcrystalline diamond films (MCD) grown without N₂ additions. These results may be used for the fabrication of NCD films and plates with high concentrations of SiV and GeV centers, which may serve as source material for the fabrication of sub-micrometer-sized luminescent diamond particles for local optical thermometry.

In this paper, we report a multi-wavelength passively Q-switched fiber laser based on reconfigurable Lyot ring filter (RLRF) and Erbium-doped fiber (EDF) saturable absorber (SA). The gain saturable absorption characteristics of the EDF are analyzed in the experiments. When EDF is used as SA, EDF exhibits different nonlinear characteristics at different pump powers. Through the observation of the experimental data, we discuss the relationship between the multi-wavelength and passively Qswitching, in view of the position of the wavelength excitations and the presence or absence of the corresponding pulse sequence. The RLRF in the structure uses a 2 m long polarization maintaining fiber (PMF), and the wavelength interval between 1.5 and 3.0 nm can be effectively switched by adjusting the polarization controller (PC). The laser elaborated can flexibly switch from a single to seven wavelengths, with a corresponding pulse repetition rates of 24.11 – 59.38 kHz, a minimum Qswitched pulse width of 1.16 μs, a maximum average output power of 46.98 μW, and a maximum single pulse energy of 9.64 nJ.

There is a growing interest in the development of transportable optical ground station (TOGS) as an important component of laser communication network. The object of this paper is a TOGS designed for optical LEO satellite downlink as well as for long-distance aircraft downlink. A composite gravity compensation mount is proposed to simplify and efficiently suppress the low-order aberrations of an 800 mm aperture primary mirror with variable orientation of the optical antenna of a TOGS as it changes pointing. In this study, first we describe the composition of the TOGS and the utility of each part. Second, taking the minimization of the primary mirror deformation as the optimization objective, we employ the particle swarm optimization algorithm to find the optima of several key structural parameters by Isight software. Next, the annular Zernike polynomials are adopted to fit the wavefront error over the entire surface of the primary mirror for describing low-order aberrations, proving that the composite mount effectively suppresses the wavefront error to smaller than ⋋ /27, as the elevation angle changes from the horizontal to the vertical one. Finally, the ZYGO interferometer wavefront detections show that, after eliminating fabrication imperfections, the RMS of the wavefront error over the entire surface of the mirrors for horizontal and vertical axes, due to deformation, are 0.04⋋ and 0.035⋋, respectively. Compared to the results of the fitted wavefront error, the relative errors are 9.5% and 8.1%. The results show the validity and feasibility of the optimized composite mount and the wavefront fitting method, which can prove its reference significance for the budget and allocation of the systematic wavefront error in meter-scale optical antenna of the TOGS for satellite downlink.

It is crucial to enhance the efficiency of terahertz radiation in a single crystal for the application of intense field terahertz waves. We devise a trapezoidal lithium niobate prism that, upon side incidence of the terahertz wave, retroreflects the femtosecond laser onto the crystal’s symmetric plane. The conversion efficiency of pump power to THz pulse power for circular cavity increases by 36% compared to that of the conventional cavity. The findings demonstrate that the utilization of sample multiplexing pump can significantly enhance the efficiency of terahertz generation.

We experimentally demonstrate for the first time a tunable orthogonal polarized Pr³⁺: LiGdF₄ dual-wavelength laser. We calculate the conditions for balancing the gain and loss of the orthogonal polarization dual-wavelength with the rotation angles, the Lyot filter, and the incident angle on the uncoated glass. By adjusting the rotation angles, the Lyot filter, and the incident angle on the uncoated glass, the continuous-wave (CW) orthogonal polarized dual-wavelength lasers operating at 519.6 and 522.8 nm, 604.5 and 607.2 nm, and 719.2 and 721.5 nm are obtained.

Single-pixel imaging allows to obtain images without the use of photosensors with spatial resolution. In this method, an image is calculated by measuring the image conformity to a given set of light patterns by a single-pixel detector. However, when implementing single-pixel imaging in practice, one has to deal with various imperfections, which lead to the difference between the experiment and the idealized theoretical model. In this work, we analyze the effect of detector noise on the ability to compute an image using a compressed sampling algorithm. By conducting computer simulations of single-pixel imaging, we investigate methods for suppressing the effects of detector noise and find optimum parameters of the measurement process. As a result, we demonstrate the ability to obtain images with a realistic model of the detector noise.

We consider the 3D coefficient inverse problem for parabolic wave equation. It involves determining the spatial distribution of refractive and absorption indices by processing phase diffraction patterns obtained by irradiating an object with a set of Gaussian beams. Unlike tomography and ptychography, rotation or scanning of the sample is not required. The problem is solved by expanding the wave field and the complex dielectric constant (varepsilon left(overrightarrow{r}right)) over the full set of Gaussian beam functions. To determine (varepsilon left(overrightarrow{r}right),) we obtain a nonlinear matrix equation. The condition of its solvability allows the selection of sampling frequencies by coordinates in accordance with the practical task.