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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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[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