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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） ▾

  • Imaging multiple Rydberg wave packets from shaper-generated two-color femtosecond pump-probe sequences

    摘要： We combine a bichromatic white light polarization pulse shaping scheme with angle- and energy-resolved photoelectron spectroscopy to image the dynamics of atomic Rydberg wave packets. Background-free detection of the Rydberg dynamics is performed using shaper-generated bichromatic linearly and circularly polarized femtosecond pump-probe pulse sequences. Photoelectron momentum distributions from linearly polarized bichromatic fields feature pronounced time-, energy-, and angle-dependent dynamics, which result from the interference of s-, d-, and g-type photoelectron wave packets from the ionization of the Rydberg np and nf series. Detailed analysis of the highly differential data allows us to extract the dynamics of both Rydberg wave packets separately. The results are experimentally verified by additional pump-probe studies with bichromatic circularly polarized pulse sequences, which exclusively map the dynamics of the Rydberg nf series via g-type photoelectron wave packets.

    关键词： Rydberg wave packets,pump-probe spectroscopy,photoelectron imaging,femtosecond lasers,polarization pulse shaping

    更新于2025-09-23 15:23:52

  • Femtosecond pump-probe spectroscopy investigation of carrier dynamics in GaAlAs photocathods

    摘要： Based on the study of GaAs photocathode, the carrier dynamics of re?ection-mode GaAlAs photocathode has been investigated. In this paper, the re?ection-mode GaAlAs/GaAs photocathode is grown by metal organic chemical vapor deposition (MOCVD) epitaxial technology. The femtosecond pump-probe spectroscopy is performed to measure carrier dynamics in GaAlAs and GaAs photocathods. After laser excitation the surfaces of GaAlAs/GaAs photocathode, the re?ectivity of photocathode surface is changed. At the same time, the dynamic processes of the non-equilibrium carrier distribution in semiconductor material is obtained by the transient re?ectance spectrum. Compared with GaAs photocathode, the Al element in GaAlAs photocathode is unfavorable to photoemission under some conditions, while it solves the problem that the spectrum response range of binary compounds is not adjustable. The change trend of initial relaxation transient of GaAs photocathode in the 22 ps range is the same as GaAlAs, while the change of GaAs and GaAlAs relaxation state is signi?cantly di?erent with the change of delay time after 22 ps. The results show that the GaAlAs increases band gap due to a signi?cantly slower than GaAs photocathode in initial process. Meanwhile, this paper provides a reference for the preparation of the GaAlAs photocathode that only respond to blue and green light range.

    关键词： Re?ectivity,Dynamic processes,Femtosecond,Re?ection-mode,Photocathodes

    更新于2025-09-23 15:23:52

  • Improved femtosecond third-order nonlinear optical properties of thin layered Cu3Nb2O8

    摘要： Thin motif-layered triclinic Cu3Nb2O8 was prepared through solid-state reaction at 700 °C, 12 h and their nonlinear optical (NLO) properties with ultrafast [800 nm, 150 fs (fs) pulses, 80 MHz repetition rate] pulse laser excitation were studied. A peculiar shift from reverse saturable absorption (RSA) to saturable absorption (SA) at a peak intensity of 40 MW/cm2 was observed. The involvement of excited state absorption (ESA) is confirmed from the decrease in the nonlinear absorption coefficient with increase in peak intensity and the observed nonlinearity is ascribed to a sequential 2 PA process (1 PA+ESA). Formation of layered structure in Cu3Nb2O8 acted as a transport layers which yielded high nonlinear absorption coefficient (7.8 × 10^{-10} m/W), nonlinear refractive index (5.17 × 10^{-16} m^2/W) and nonlinear optical susceptibility (25.6 × 10^{-11} esu) when compared to other known copper niobates. The observation of low onset-limiting threshold (78.79–26.26 μJ/cm^2) renders Cu3Nb2O8 a prospective material for ultrashort pulse laser protecting device and biomedical microsurgery tools. A transition of mixed phase CuNb2O6-Cu3Nb2O8 into pure triclinic Cu3Nb2O8 along with change in morphology from pore to layered structure with increase in sintering time was confirmed from powder XRD, Raman, FESEM measurements and UV–Visible absorption studies.

    关键词： Femtosecond,Copper niobate,Optical limiting,Z-scan

    更新于2025-09-23 15:23:52

  • Pressure dependence of high order harmonic generation in nitrogen molecular gas and atmospheric air

    摘要： The effect of the variation of the gas pressure on the high harmonic generation (HHG) from nitrogen molecular gas (N2) and atmospheric air with ultrashort intense laser pulses is measured. The optimum pressure in the interaction region of a gas jet for maximizing the HHG yield is determined for both gases. Enhancement of the HHG output and its extension to higher harmonic orders are observed around the optimum pressure value of 0.33 bar. Theoretical calculations based on one-dimensional models explain this effect and provide reasonable agreement with experimental results.

    关键词： Femtosecond laser,Conversion efficiency,High-order harmonic generation (HHG),Phase matching,XUV radiation,Pressure optimization

    更新于2025-09-23 15:23:52

  • Electron transfer from photoexcited naphthalene-1,4:5,8-bis(dicarboximide) radical anion to Mn(bpy)(CO)3X and Re(bpy)(CO)3X CO2 reduction catalysts linked via a saturated methylene bridge

    摘要： Supramolecular systems that connect a naphthalene-1,4:5,8-bis(dicarboximide) (NDI) radical anion donor to Mn(bpy)(CO)3Br or Re(bpy)(CO)3Cl CO2 reduction catalysts via a methylene bridge have been synthesized and studied by femtosecond transient visible, near-infrared and mid-infrared spectroscopy. The use of the methylene bridge to link NDI to the complexes does not affect the reduction potentials of the metal complexes. Selective photoexcitation of NDI?? to 2*NDI?? results in ultrafast reduction of the bipyridine (bpy) ligands on both the Mn and Re complexes to form Mn(I)(bpy??)(CO)3X and Re(I)(bpy??)(CO)3X in near unity quantum yield, respectively. The initial formation of Mn(I)(bpy??)(CO)3X is unexpected based on previous electrochemical data that indicates the Mn(I) center is reduced at a more positive potential than the bpy ligand. Moreover, the rate of forward electron transfer in the Mn complex was found to be faster than in the Re complex, while the rate of the back electron transfer in the Re complex was faster than in the Mn complex.

    关键词： Electrochemistry,CO2 reduction,Electron transfer,Radical anions,Femtosecond spectroscopy,Solar energy

    更新于2025-09-23 15:23:52

  • Possibilities for serial femtosecond crystallography sample delivery at future light sourcesa)

    摘要： Serial femtosecond crystallography (SFX) uses X-ray pulses from free-electron laser (FEL) sources that can outrun radiation damage and thereby overcome long-standing limits in the structure determination of macromolecular crystals. Intense X-ray FEL pulses of sufficiently short duration allow the collection of damage-free data at room temperature and give the opportunity to study irreversible time-resolved events. SFX may open the way to determine the structure of biological molecules that fail to crystallize readily into large well-diffracting crystals. Taking advantage of FELs with high pulse repetition rates could lead to short measurement times of just minutes. Automated delivery of sample suspensions for SFX experiments could potentially give rise to a much higher rate of obtaining complete measurements than at today’s third generation synchrotron radiation facilities, as no crystal alignment or complex robotic motions are required. This capability will also open up extensive time-resolved structural studies. New challenges arise from the resulting high rate of data collection, and in providing reliable sample delivery. Various developments for fully automated high-throughput SFX experiments are being considered for evaluation, including new implementations for a reliable yet flexible sample environment setup. Here, we review the different methods developed so far that best achieve sample delivery for X-ray FEL experiments and present some considerations towards the goal of high-throughput structure determination with X-ray FELs.

    关键词： automation,serial femtosecond crystallography,X-ray free-electron laser,sample delivery,high-throughput

    更新于2025-09-23 15:22:29

  • Systematic λ/21 resolution achieved in nanofabrication by two-photon-absorption induced polymerization

    摘要： Photopolymerization, based on two-photon absorption in resins, has been recognized as one of the enabling technologies to fabricate three-dimensional micro/nanostructures with a sub-diffraction-limit resolution. This work focuses on improving the spatial resolution using femtosecond laser, λ=780 nm, with a systematic nanofabrication process which we developed. We discuss the factors influencing the spatial resolution, including the laser intensity, the exposure time, and the scanning speed by fabricating polymerized-voxels, nano-lines, and suspended nano-fibers in a photoresist based on a methyl-methacrylate monomer. We show that a resolution of ~36 nm, corresponding to ~λ/21, is achieved. Stable 3D microstructures can be fabricated by using our custom made set up.

    关键词： Voxel,Resolution,Two Photon Polymerization,Micro/Nanostructures,Femtosecond Laser,Suspended Polymerized Fibers

    更新于2025-09-23 15:22:29

  • Compression of femtosecond pulses in a wide wavelength range using a large-mode-area tapered fiber

    摘要： We report the design of a tapered fiber that can be used for the compression of pulses at different central wavelengths. The proposed fiber is a three-layer W-type large-mode-area fiber, which has been tapered to transform the mode area from 1700 μm2 to 900 μm2. We determine the exact length of the maximum pulse compression and numerically demonstrate the compression of a 250 fs, 100 kW peak power input pulse to 15 fs, 850 kW at 1.55 μm wavelength and compression of 250 fs, 120 kW peak power input pulses to 28 fs, 700 kW and to 46 fs, 500 kW at 1.8 μm and 2 μm wavelengths, respectively. Such a fiber can find wide ranging applications, including in communication, spectroscopy and medicine.

    关键词： ultrafast processes in fiber,large-mode-area fiber,high peak power femtosecond pulses,pulse shaping,tapered fiber,pulse compression

    更新于2025-09-23 15:22:29

  • Femtosecond Optical Annealing Induced Polymer Melting and Formation of Solid Droplets

    摘要： Interaction between femtosecond laser pulses with polymeric thin films induced transient optical annealing of the polymer molecules. Melting of the polymer films took place during the transient annealing process, so that a solid-liquid-solid phase transition process was observed. Ultrafast cooling of the melting polymer produced solidified droplets. Microscopic and spectroscopic characterization revealed that the polymer molecules were rearranged with preferable H-aggregation to reach the lowest formation energy during the melting process. Intermolecular coupling was enhanced due to the modified molecular arrangement. This observation of melting of polymeric semiconductors due to the interaction with femtosecond light pulses is potentially important for better understanding laser-matter interactions and for exploring organic optoelectronic devices through special material processing.

    关键词： transient optical annealing,melting polymer droplets,solid-liquid-solid phase transition,femtosecond laser-matter interaction,molecular rearrangement

    更新于2025-09-23 15:22:29

  • Bio-Molecular Applications of Recent Developments in Optical Tweezers

    摘要： In the past three decades, the ability to optically manipulate biomolecules has spurred a new era of medical and biophysical research. Optical tweezers (OT) have enabled experimenters to trap, sort, and probe cells, as well as discern the structural dynamics of proteins and nucleic acids at single molecule level. The steady improvement in OT’s resolving power has progressively pushed the envelope of their applications; there are, however, some inherent limitations that are prompting researchers to look for alternatives to the conventional techniques. To begin with, OT are restricted by their one-dimensional approach, which makes it difficult to conjure an exhaustive three-dimensional picture of biological systems. The high-intensity trapping laser can damage biological samples, a fact that restricts the feasibility of in vivo applications. Finally, direct manipulation of biological matter at nanometer scale remains a significant challenge for conventional OT. A significant amount of literature has been dedicated in the last 10 years to address the aforementioned shortcomings. Innovations in laser technology and advances in various other spheres of applied physics have been capitalized upon to evolve the next generation OT systems. In this review, we elucidate a few of these developments, with particular focus on their biological applications. The manipulation of nanoscopic objects has been achieved by means of plasmonic optical tweezers (POT), which utilize localized surface plasmons to generate optical traps with enhanced trapping potential, and photonic crystal optical tweezers (PhC OT), which attain the same goal by employing different photonic crystal geometries. Femtosecond optical tweezers (fs OT), constructed by replacing the continuous wave (cw) laser source with a femtosecond laser, promise to greatly reduce the damage to living samples. Finally, one way to transcend the one-dimensional nature of the data gained by OT is to couple them to the other large family of single molecule tools, i.e., fluorescence-based imaging techniques. We discuss the distinct advantages of the aforementioned techniques as well as the alternative experimental perspective they provide in comparison to conventional OT.

    关键词： plasmonic optical tweezers,femtosecond optical tweezers,photonic crystal optical tweezers,fluorescence,single molecule and cell studies

    更新于2025-09-23 15:22:29