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Femtosecond Pulse Laser Near-Field Ablation of Ag Nanorods
摘要： Ag nanorods (Ag NRs) with a mean aspect ratio of 3.9 were prepared through a wet-chemical method, and the absorption spectra for various aspect ratios were obtained. The morphology transformation of Ag NRs irradiated with a femtosecond pulse laser was investigated through transmission electron microscopy (TEM). The near-field ablation was dependent on the laser polarization and wavelength. Laser-induced high electric field intensity was observed at the ends, middle, and junctions of the Ag NRs under various ablation conditions. Through simulation, the evolution mechanism was analyzed in detail. The effect of laser polarization angle on plasmonic junction welding was also investigated. By controlling the electronic field distribution, several nanostructures were obtained: bone-shaped NRs, T-shaped NRs, dimers, trimers, curved NRs, and nanodots. This study suggests a potentially useful approach for the reshaping, cutting, and welding of nanostructures.
关键词： femtosecond pulse laser,polarization,Ag nanorods,near-field ablation
更新于2025-11-14 17:04:02
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Intercellular Trafficking of Gold Nanostars in Uveal Melanoma Cells for Plasmonic Photothermal Therapy
摘要： Efficient plasmonic photothermal therapies (PPTTs) using non-harmful pulse laser irradiation at the near-infrared (NIR) are a highly sought goal in nanomedicine. These therapies rely on the use of plasmonic nanostructures to kill cancer cells while minimizing the applied laser power density. Cancer cells have an unsettled capacity to uptake, retain, release, and re-uptake gold nanoparticles, thus offering enormous versatility for research. In this work, we have studied such cell capabilities for nanoparticle trafficking and its impact on the effect of photothermal treatments. As our model system, we chose uveal (eye) melanoma cells, since laser-assisted eye surgery is routinely used to treat glaucoma and cataracts, or vision correction in refractive surgery. As nanostructure, we selected gold nanostars (Au NSs) due to their high photothermal efficiency at the near-infrared (NIR) region of the electromagnetic spectrum. We first investigated the photothermal effect on the basis of the dilution of Au NSs induced by cell division. Using this approach, we obtained high PPTT efficiency after several cell division cycles at an initial low Au NS concentration (pM regime). Subsequently, we evaluated the photothermal effect on account of cell division upon mixing Au NS-loaded and non-loaded cells. Upon such mixing, we observed trafficking of Au NSs between loaded and non-loaded cells, thus achieving effective PPTT after several division cycles under low irradiation conditions (below the maximum permissible exposure threshold of skin). Our study reveals the ability of uveal melanoma cells to release and re-uptake Au NSs that maintain their plasmonic photothermal properties throughout several cell division cycles and re-uptake. This approach may be readily extrapolated to real tissue and even to treat in situ the eye tumor itself. We believe that our method can potentially be used as co-therapy to disperse plasmonic gold nanostructures across affected tissues, thus increasing the effectiveness of classic PPTT.
关键词： nanoparticle endocytosis,femtosecond pulse laser,nanoparticle exocytosis,gold nanostars,plasmonic photothermal therapy
更新于2025-09-23 15:21:01
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Control of Multiple Filamentation of Femtosecond Laser Pulses in Air
摘要： The results are presented of experiments on controlling the characteristics of the multiple filamentation domain of femtosecond laser pulses along atmospheric paths via variations in the initial spatial focusing, beam radius, and pulse energy, as well as the optical field structure at the initial beam aperture.
关键词： filamentation,femtosecond pulse,bimorph deformable mirror,laser radiation,postfilamentation light channel,self-focusing
更新于2025-09-23 15:21:01
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Investigation of optical fiber-tip probes for common and ultrafast SERS
摘要： In this study, we performed a three-dimensional computational experiment on ultrashort pulse propagation in an optical fiber-tip probe that is decorated with gold nanoparticles (NPs) using a constant structure for the probe’s dielectric taper and different spatial configurations of the gold nanoparticles. Interestingly, a hot spot with the highest amplitude of the electric field was found not along the same chain of the NPs but between terminal NPs of neighboring chains of NPs at the probe’s tip (the amplitude of the electric field in the hot spots between the NPs along the same chain was of the order of 101, while that between terminal NPs of neighboring chains was of the order of 103). We eventually identified a configuration with only six terminal nanoparticles (Config4) which is characterized by the highest electric field amplitude enhancement and can provide the highest spatial resolution in the SERS interrogation of an object of interest. The ultrashort temporal responses of the hot spots for all configurations exhibited relatively high pulse elongation (relative elongation was greater than 4.3%). At the same time, due to the reflection of the incident pulse and consequent interference, the temporal responses of most hot spots contained several peaks for all configurations except for the optimum Config4. Nonetheless, the ultrashort temporal responses of all hot spots for Config4 were characterized by a single peak but with a relatively large pulse elongation (relative elongation was 234.1%). The results indicate that further examination of this new structure of a nanoparticles-coated optical fiber-tip probe with only six terminal NPs may provide attractive characteristics for its practical applications.
关键词： gold nanoparticles,femtosecond pulse,optical fiber-tip probe,ultrafast nanophotonics.,surface-enhanced Raman spectroscopy,temporal response
更新于2025-09-23 15:19:57
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Interference microscopy study of the preplasma formed on an iron target surface exposed to high-power femtosecond laser pulses
摘要： The characteristic scale of spread of the plasma formed on the surface of a bulk iron target irradiated by a femtosecond laser pulse with an intensity of 1016 W cm–2 is measured by time-resolved interference microscopy using femtosecond pulses emitted by a Cr : forsterite laser system with an intensity contrast of 107. The chosen technique is demonstrated to be efficient in such measurements. It is shown experimentally that, as a result of laser pulse impact, the displacement of a plasma layer with a density exceeding critical does not exceed 30 nm.
关键词： interference microscopy,femtosecond pulse,electron acceleration mechanisms,hot electrons
更新于2025-09-23 15:19:57
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[IEEE 2019 Joint Conference of the IEEE International Frequency Control Symposium anEuropean Frequency and Time Forum (EFTF/IFC) - Orlando, FL, USA (2019.4.14-2019.4.18)] 2019 Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum (EFTF/IFC) - All Polarization-Maintaining Fiber Laser for Femtosecond Pulse Generation at NTSC
摘要： We report on a robust mode-locked femtosecond fiber laser based on a nonlinear optical mirror with all polarization-maintaining fibers. Stable and self-starting operation is obtained by exploiting an integrated nonreciprocal device biases π/2 phase shift. In the single-pulse region, the laser directly generates output power of 3.15 mW at repetition rate of 87.7 MHz, corresponding to the pulse energy of 37 pJ. The center wavelength is 1585 nm with the spectral bandwidth of 25 nm at the maximum output power. We also evaluate the relative intensity noise of the mode-locking laser.
关键词： Femtosecond pulse,Optical frequency comb,Mode-locked fiber laser
更新于2025-09-16 10:30:52
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Generation of Low-Frequency Radiation Under the Laser Pulse Effect on a Plasma in a Magnetic Field
摘要： We reveal the possibility of a low-frequency radiation generation at a normal incidence of the laser pulse on a dense plasma in a constant magnetic ?eld. The generation occurs due to the motion of electrons under the magnetic ?eld e?ect and a ponderomotive force slowly varying with time localized in the skin layer where the laser radiation penetrates. The characteristic radiation frequencies are determined by the inverse duration of the laser pulse. We ?nd the ?eld strength of the radiation generated and its dependences on the Larmor frequency of electrons and the plasma and laser pulse parameters.
关键词： magnetic ?eld,terahertz radiation,ponderomotive force,femtosecond pulse,nonlinear current
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Numerical and Experimental Study on the IR Femtosecond Laser and Phase Mask-Based Grating Inscription in Photonic Crystal Fibers
摘要： Femtosecond pulse laser sources enable the fabrication of fiber Bragg gratings (FBGs) in non-photosensitive fibers, allow for through coating grating inscription when working at infrared (IR) wavelengths and can provide for high temperature stable gratings. Target applications for such gratings include, but are not limited to, optical communications, fiber lasers and fiber sensing. When dealing with such grating inscription method in photonic crystal fibers (PCF) however, the presence of air holes in the fiber cladding impedes the delivery of the femtosecond laser pulse energy to the fiber core, which in its turn significantly affects the index change through non-linear absorption processes in the fiber core [1]. Our research focuses on this issue in view of understanding how the grating writing laser pulses interact with the PCF’s holey structure and of enabling more efficient femtosecond laser-based inscription of FBGs in PCFs. Here we report on the inscription of FBGs in a hexagonal lattice PCF using a femtosecond pulse laser operating at 1030 nm with a phase mask and a short focal length cylindrical lens (f=10 mm) that focuses light to the fiber core [2]. We first looked into the influence of the alignment on laser beam focusing in the cross-section of the PCF by comparing the focusing characteristics to those in standard step-index single mode fiber. As a figure of merit, we used the transverse coupling efficiency (TCE), which is defined as the ratio of the integrated core field intensities simulated (using Lumerical FDTD Solutions?) in the presence and absence of holey cladding. Fig. 1b shows how the TCE changes as the fiber is translated along the X and Y axes in the cross-sectional plane. X=0 and Y=0 corresponds to focused to the center of the core, and negative Y indicates translation of the fiber away from the lens (see Fig. 1a). For a step-index fiber we observe a typically elongated region in which we find optimal coupling with TCE=1 (no air holes) for a beam waist of 2.34 μm and a depth of focus of 15.7 μm. Fig. 1c shows an alignment map for a hexagonal lattice PCF (with structure shown in the inset of Fig. 1d), when light is incident along the ΓK axis of the hexagon. We can identify three distinct regions with a TCE around 0.6. Those appear when the fiber is shifted by around 15 μm and 30 μm further from the lens. This offset indicates that optimal coupling of the grating writing beam to the PCF core requires focusing to the edge of the holey cladding or closer to the silica cladding region of the fiber, rather than to the core center. Fig. 1 a) Fiber translational axes and translation dependence of the transverse coupling efficiency (TCE) for b) step-index fiber and c) PCF. d) Spectra of the IR femtosecond pulse inscribed FBG in the PCF (SEM image in the inset). We then inscribed FBGs in the above mentioned hexagonal lattice PCF with a commercial Yb:KGW ultrafast regenerative amplifier system Pharos 6W (Light Conversion) at 1030 nm and 190 fs duration pulses at a repetition rate of 100 Hz. We used high accuracy alignment stages to find the best coupling position by monitoring the luminescence (around 420 nm) from the Ge-doped core. The reflection and transmission spectra of the inscribed FBG are shown in Fig. 1c. We achieved an almost 4 dB strong FBG in around 4 seconds using a laser power of 450 mW. To the best of our knowledge it is the first time that the difference between regular step-index fibers and PCFs in best focusing conditions for IR femtosecond laser-based FBG writing is studied and that such a FBG is realized in a PCF using a 1030 nm source and a phase mask technique with a short focal length cylindrical lens.
关键词： phase mask,photonic crystal fibers,Femtosecond pulse laser,fiber Bragg gratings,transverse coupling efficiency
更新于2025-09-12 10:27:22
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Resonance Enhancement in Laser-Produced Plasmas (Concepts and Applications) || Resonance Enhancement of Harmonics in Metal-Ablated Plasmas: Early Studies
摘要： In this subsection, the first observation of an exceptionally strong resonance enhancement of a single harmonic in a plateau region is described. This phenomenon was observed during investigations of harmonic generation from femtosecond pulse interacting with indium plasma. A very strong 13th harmonic generation (λ = 61.2 nm), almost 2 orders of magnitude, exceeding the intensities of neighboring harmonics in the plateau range was observed in those studies [1].
关键词： harmonics,femtosecond pulse,extreme ultraviolet,indium plasma,resonance enhancement
更新于2025-09-11 14:15:04