Journal of Russian Laser Research最新文献

In this paper, for the first time, we propose an LD-end-pumped thermal compensation Q-switched step concentration Tm : YAG laser. A novel step concentration Tm : YAG crystal is used as the laser medium to mitigate the severe thermal effects typically encountered in single-doped Thulium crystals. To compensate the thermal lens effect generated by the crystal, we insert a negative lens into the cavity. At a repetition frequency of 100 Hz, an output energy of 7.82 mJ with a pulse width of 152.4 ns is achieved. The center wavelength is 2013.41 nm, and the beam quality is characterize by (mathrm{M}_{x}^{2}=1.34) and (mathrm{M}_{y}^{2}=1.39).

We study low-temperature photoluminescence of CdTe:Fe single crystals in the near-IR range at Helium temperatures. We establish that doping with 4 · 10¹⁸ cm⁻³ iron concentration leads to a decrease of the band gap by 8 ± 1 meV compared to non-doped CdTe. We show that, in the spectral range of 1.2–1.6 eV, the luminescence of crystals is mainly defined by Hydrogen-like donors and two types of acceptors with binding energies of 149 ± 5 meV and 45 ± 2 meV. In addition, we detect the luminescence bands with maxima of 1.1 eV and 0.95 eV in the longer wavelength region. The characteristic decay time for each of the bands is 0.386 ms at 7 K. The observed bands are ascribed to intracenter luminescence corresponding to the ³T₁(³H) → ⁵E(⁵D) and ⁵T₂(⁵D) → ⁵E(⁵D) transitions between Fe²⁺-ion inner shells. Detection and identification of these bands allows the use of the near-IR range for the study of optically active iron ions in promising laser media based on CdTe:Fe.

We report a Q-switched Er³⁺:ZBLAN fiber laser based on Vanadium Aluminum carbide (V₄AlC₃) as a saturable absorber (SA). Our SA is fabricated by depositing V₄AlC₃ nanoparticles on a gold mirror to form an SA film. The proposed laser operates at the 2784.32 nm central wavelength with a 1.68 nm 3 dB bandwidth. The maximum pulse energy and output power are 3.51 µJ and 490 mW at a maximum pump power of 6.6 W. To the best of our knowledge, this is the first time that V₄AlC₃ provides Q-switching in the 3 µm region. The proposed SA is promising for mid-infrared pulsed lasers.

We derive analytical formulas for average intensity of a partially coherent elliptical vortex (PCEV) beam propagating in a turbulent atmosphere along an uplink path and a downlink path with the help of the extended Huygens–Fresnel principle. Our outcomes reveal that the normalized initial profile with the elliptical annular dark pattern splits and rotates counterclockwise around the major axis of elliptical hollow pattern with increasing the propagation distance in free space and atmospheric turbulence. We also find that the splitting light spots heal into a Gaussian-like spot due to the turbulence effect, smaller ellipticity, larger topological charge, slower healing process. It can be also found that PCEV beam propagates along a downlink path is less affected by atmospheric turbulence in comparison with uplink path. In order to confirm our numerical results, we combine the complex screen method and multi-phase screen method to simulate the propagation of the PCEV beam in atmospheric turbulence. It is indicated that the simulation results are in good agreement with theoretical results. Our findings may be of great significance for the development of the free-space optical communications.

In this work, we demonstrate stable multi-bit (discrete) modulations of the optical properties of thin-film GST₂₂₅ (Ge₂Sb₂Te₅ or GST) samples as a result of phase transitions induced by femtosecond (≈ 50 fs) laser pulses. An ultra-high crystallization rate of the SET material is shown, ~13 m/s. One- and many-step modulations of optical properties are obtained during crystallization of the sample material. Reamorphization or RESET of the samples occurs at a rate of 5–6 m/s; it is realized in several impacting pulses. This fact indicates the thermal nature of the phase transitions.

In this paper, we report on a high-power Tm : YAP cavity-dumped laser capable of simultaneously achieving high repetition rates and short nanosecond pulses. The laser employs a Pockels cell (PC) composed of a La₃Ga₅SiO₁₄ (LGS) crystals as an electro-optical Q-switch, which overcomes the limitations of piezoelectric ringing effects on the highest operating repetition rates and thermally-induced depolarization on the maximum operating power. A stabilized pulsed laser output at 1942 nm, with a pulse repetition rate of 20 kHz, a pulse duration of 6.0 ns, and an average output power of 15.0 W, is obtained at a pump power of 150 W. The beam quality factor M² is 1.36 in the vertical direction and 1.18 in the horizontal direction.

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.