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oe1(光电查) - 科学论文

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出版时间
  • 2020
研究主题
  • fast processes in solids
  • femtosecond interferometry
  • femtosecond laser radiation
应用领域
  • Optoelectronic Information Science and Engineering
机构单位
  • Prokhorov General Physics Institute, Russian Academy of Sciences; National Research Nuclear University MEPhI
441 条数据
?? 中文（中国） ▾

  • Second harmonic generation at 544a??nm of a femtosecond laser

    摘要： We study second harmonic generation (SHG) at 544 nm of the 0-type (e + e - e) quasi-phase-matching based on a femtosecond laser at 1088 nm. The green pulse with the spectrum width of 0.6 nm and the peak power of 17.7 kW is obtained at the pump power density of 2.81 GW/cm2 and the conversion e?ciency is 21 %. As the propagation distance along the PPMgLN crystal increases, the spectrum at 544 nm becomes narrower and narrower and the pulse duration broadens very seriously.

    关键词： Group velocity match,544 nm laser,Second harmonic generation,PPMgLN,Ultrafast optics,Femtosecond pulses

    更新于2025-09-23 15:21:01

  • Fabrication of large-scale freestanding THz wire grid polarizers by femtosecond laser micromachining

    摘要： High-performance THz polarizers, as a quasi-optical device to manipulate THz waves, are highly demanded for THz spectroscopy and imaging applications. In this work, we have employed the femtosecond laser micro-machining technique to fabricate freestanding THz wire grid polarizers with two kinds of reinforced line structures which weaken the e?ects of gravity sagging and entanglement of long free wires, thus enabling large-scale processing. The e?ect of the reinforced lines on the polarizers were simulated by the Finite-Di?erence Time-Domain (FDTD) method, and the performances of the polarizer were characterized by THz time-domain spectroscopy and compared with that of a commercial wire gird polarizer. The calculated transmittance is in good agreement with the FDTD results. The degree of polarization and the extinction ratio of the polarizer with discontinuous reinforced lines are better than those of a commercial wire grid polarizer.

    关键词： Time-domain THz spectroscopy,THz,Femtosecond laser micro-machining,Wire grid polarizer

    更新于2025-09-23 15:21:01

  • Correlation between laser spectroscopic studies and mechanical characterization of zirconia-based multiwall carbon nanotube ceramic composites

    摘要： The hardness of zirconium oxide-based ceramic nanocomposites was correlated with the laser spectroscopic studies by analyzing the samples through nanosecond and femtosecond laser to see the viability of this technique as a fast and in situ for assessment of mechanical properties in nuclear industry. Zirconia incorporated with different vol% of multiwall carbon nanotubes were processed by the high frequency induction heated sintering. The composites were characterized by the nanosecond laser-induced breakdown spectroscopy (LIBS) with optimized delay time of 1, 2, and 3 μs and 200 and 300 mJ energies generated by laser Nd:YAG (λ = 1064 nm). The plasma temperature resulted by the ablation of different samples was estimated through intensity of selected zirconium lines using the Boltzmann plot method. The samples were mechanically characterized by the Vickers hardness test. The estimated plasma temperature and the ratio of Zr(II) with different intensities of Zr(I) emission lines show rather weak dependency and increase with surface hardness. The samples were scrutinized by the femtosecond laser micromachining through variation in depth and surface morphology of machined areas. It is found that deeper circular groove and enhanced erosion of disk shape by femtosecond laser machining are achieved for less hard materials and are in agreement with the LIBS analysis.

    关键词： LIBS,Ceramics,Machining,Femtosecond,Nanocomposites

    更新于2025-09-23 15:21:01

  • Engineering of high quality factor THz metasurfaces by femtosecond laser ablation

    摘要： We report on the realization of high Q metasurfaces operating in the THz frequency range by femtosecond laser ablation applied to a nanometric metallic layer over a silicon substrate. Two different fabrication methods are used to develop periodic patterns whose basic elements are in form of an array of through-holes or metallic islands. The response of the resulting structures is characterized using a time-domain spectrometer in the frequency range 0.3–1.5 THz. The experimental findings are compared with the predictions of full wave electromagnetic simulations. The fairly good agreement between simulation predictions and experimental findings evidences that the proposed approach can offer a facile way to the elaboration of THz metasurfaces.

    关键词： Femtosecond laser ablation,THz,High quality factor,Metasurfaces

    更新于2025-09-23 15:21:01

  • Simultaneous Nano-Texturing onto a CVD-Diamond Coated Piercing Punch with Femtosecond Laser Trimming

    摘要： In this study, a CVD (Chemical Vapor Deposition)-diamond coated tungsten carbide cobalt (WC (Co)) punch was trimmed to adjust its surface roughness and to significantly reduce its edge curvature for fine piercing by femtosecond laser processing. Through this laser trimming, the surface quality of the diamond coating and the punch edge profile were improved to less than 0.5 μm at the maximum roughness and 2 μm in the edge width, respectively. In parallel with this improvement of surface quality, the side surface of the diamond coating was modified to include nano-textures via the LIPSS (Laser Induced Periodic Surface Structuring) process. Through the fine piercing process, this nanotexture was transcribed onto the pierced hole surface together with fine shearing of the hole by piercing. WLI (White-Light Interferometry) and SEM (Scanning Electron Microscopy) were utilized to describe this transcription of nanotextures during the piercing process. These semi-regular nanotextures with an LIPSS period of 300 nm on the pierced hole surface induced a blue colored surface plasmon.

    关键词： diamond-coated WC (Co) punch,concurrent transcription of nanotextures,surface plasmon,simultaneous nanotexturing,femtosecond laser trimming,fine piercing

    更新于2025-09-23 15:21:01

  • Investigation and Prediction on Regulation of Hydrophobicity of Polymethyl Methacrylate (PMMA) Surface by Femtosecond Laser Irradiation

    摘要： This study presents the contact angle prediction model of a trapezoidal groove structure based on the laser irradiation on polymethyl methacrylate (PMMA). The trapezoidal groove structure was designed and proposed according to the characteristics of a femtosecond laser. First, the complete wetting model and incomplete wetting model which were compatible with the characteristics of the laser mechanism were constructed based on the Gibbs free energy and the structural parameters of the trapezoidal groove structure. Then, based on the contact angle prediction models constructed, the samples were divided into two groups according to the designed structural parameters, and the experimental investigations were carried out. The result demonstrated that the incomplete wetting prediction model was more in line with the actual situation. The convex width and the top edge length of spacing of the trapezoidal groove structure both affected the contact angle prediction results. From both the experimental contact angles and the contact angles predicted by the incomplete wetting model, it could be known that the contact angle reached 138.09° when the ratio of the convex width to the top edge length of spacing was 0.25, indicating that the smaller the ratio of the convex width to the top edge length of spacing, the better the hydrophobicity of PMMA.

    关键词： femtosecond laser,trapezoidal groove structure,polymethyl methacrylate,hydrophobicity

    更新于2025-09-23 15:21:01

  • Spiky Nickel Electrodes for Electrochemical Oxygen Evolution Catalysis by Femtosecond Laser Structuring

    摘要： Micro- and nanostructured Ni/NiO surfaces were generated by femtosecond laser structuring for oxygen evolution reaction in alkaline water electrolysis cells. For two different angles between the laser beam and the nickel surface, two different types of laser-structured electrodes were prepared, characterized, and compared with a plane tempered nickel electrode. Their electrochemical activities for the oxygen evolution reaction were tested by using cyclic and linear sweep voltammetry. The chemical surface composition was investigated by X-ray photoelectron spectroscopy. Laser structuring increased the overall electrochemical performance by more than one order of magnitude. The overpotential of the laser-structured electrodes for the oxygen evolution reaction was decreased by more than 100 mV due to high defect densities of the structures created by the laser ablation process.

    关键词： nickel electrodes,femtosecond laser structuring,alkaline water electrolysis,electrochemical catalysis,oxygen evolution reaction

    更新于2025-09-23 15:21:01

  • Five kHz thermometry in turbulent spray flames using chirped-probe-pulse femtosecond CARS, part II: Structure of reaction zones

    摘要： Temperature was measured in turbulent spray flames of ethanol and acetone stabilized on the piloted Sydney Needle Spray Burner (SYNSBURN TM) using single-laser-shot, chirped-probe-pulse femtosecond coherent anti-Stokes Raman spectroscopy (CPP-fs-CARS) with a repetition rate of 5 kHz. The burner features air-blast atomization of liquid injected from a needle that can be translated by a length Lr within a co-flowing air stream so that piloted spray flames ranging from dilute to dense can be studied. Part I of these investigations has reported on the CPP-fs-CARS technique and extensive details of data processing methodology. Part II is concerned with the structure of the reaction zones at different spray loadings and for different departures from blow-off. While not performed simultaneously, measurements of the size distribution of liquid fragments are also reported and discussed in conjunction with the measured temperature. Measured probability density functions of temperature show that for flames with the same liquid loading but different recess lengths, Lr, the near-field spray structure that forms upstream of x/D = 10 affects flame structure and stability further downstream. As the spray exiting the burner becomes denser, with a higher proportion of ligaments and 'irregular' shaped objects, the entrainment of hot pilot gases into the spray envelope is affected, hence changing the rates of vaporization and subsequent combustion. The reported results will also form a useful platform for validating sub-models of atomization and combustion in turbulent, dilute to dense spray flames.

    关键词： Femtosecond-CARS,Temperature measurements,Turbulent spray flames

    更新于2025-09-23 15:21:01

  • Ytterbium-doped fibre femtosecond laser offers robust operation with deep and precise microsurgery of C. elegans neurons

    摘要： Laser microsurgery is a powerful tool for neurobiology, used to ablate cells and sever neurites in-vivo. We compare a relatively new laser source to two well-established designs. Rare-earth-doped mode-locked fibre lasers that produce high power pulses recently gained popularity for industrial uses. Such systems are manufactured to high standards of robustness and low maintenance requirements typical of solid-state lasers. We demonstrate that an Ytterbium-doped fibre femtosecond laser is comparable in precision to a Ti:Sapphire femtosecond laser (1–2 micrometres), but with added operational reliability. Due to the lower pulse energy required to ablate, it is more precise than a solid-state nanosecond laser. Due to reduced scattering of near infrared light, it can lesion deeper (more than 100 micrometres) in tissue. These advantages are not specific to the model system ablated for our demonstration, namely neurites in the nematode C. elegans, but are applicable to other systems and transparent tissue where a precise micron-resolution dissection is required.

    关键词： Ytterbium-doped fibre femtosecond laser,Laser microsurgery,neuronal regeneration,Ti:Sapphire femtosecond laser,solid-state nanosecond laser,C. elegans

    更新于2025-09-23 15:19:57

  • Simulation of femtosecond interferometry when studying the effect of intense laser irradiation of a transparent medium

    摘要： A method for comparing experimental and simulation results obtained when transmitting a femtosecond laser pulse through a material is proposed. This method is based on computer reproduction of photographs recorded using femtosecond interferometry. A numerical analysis of the spatial and temporal evolution of an intense (~1013 W cm–2) pulse propagating in the bulk of yttrium aluminium garnet is presented.

    关键词： fast processes in solids,femtosecond interferometry,femtosecond laser radiation

    更新于2025-09-23 15:19:57