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A Method for Expansion of Z-Directional Measurement Range in a Mode-Locked Femtosecond Laser Chromatic Confocal Probe
摘要： A method is proposed to expand the Z-directional measurement range of a fiber-based dual-detector chromatic confocal probe with a mode-locked femtosecond laser source. In the dual-detector chromatic confocal probe, the Z-directional displacement of a measurement target is derived from the peak wavelength in the normalized intensity ratio from the two light intensities obtained by the two identical fiber detectors. In this paper, a new method utilizing the main-lobe and side-lobes of axial responses acquired from both the normalized intensity ratio Ia and the invert normalized intensity ratio In, which is the inverse of Ia, is proposed to obtain the seamless relationship between the peak wavelength and the Z-directional displacement of a measurement target. Theoretical calculations and experimental investigation are carried out to demonstrate the feasibility of the proposed measurement range expansion method.
关键词： measurement range expansion,side-lobe,femtosecond laser,chromatic confocal probe
更新于2025-11-28 14:24:03
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[IEEE 2018 IEEE Sensors - New Delhi (2018.10.28-2018.10.31)] 2018 IEEE SENSORS - Highly Sensitive Refractometer Using a Fiber Bragg Grating Fabricated by Femtosecond Laser
摘要： A highly localized fiber Bragg grating is inscribed using point-by-point femtosecond laser direct writing technique. By monitoring the location of the cut off wavelength, we demonstrate that the FBG has a highly-linear sensitivity for refractive index (RI) measurement. By monitoring the “peak-to- dip” intensity change near the cut-off wavelength, an ultra-high refractive index sensitivity of 2924.3dB/RIU and a RI resolution of 3.4×10-7 are achieved. As different surrounding refractive index corresponds to different location of the cut off wavelength, this FBG based refractometer can measure RI with wide range measurement range together with high sensitivity.
关键词： Femtosecond laser,Fiber Bragg grating,Refractive index sensors
更新于2025-11-28 14:23:57
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In vitro bioactivity and biocompatibility of femtosecond laser-modified Ti6Al4V alloy
摘要： The present work investigates bioactivity and biocompatibility of femtosecond (fs) laser surface-modified Ti6Al4V alloy (Ti-alloy). Self-aligned conical surface features were generated on Ti-alloy when laser irradiated employing a Ti:sapphire pulsed fs laser of wavelength 800 nm. Modification of surface chemical composition resulting from fs-laser irradiation of Ti-alloy was examined using Grazing incidence X-ray diffraction (GIXRD) technique and micro-Raman spectroscopy. Sub-oxide phase of titanium was detected on Ti-alloy surface post-fs-laser irradiation leading to increased oxygen vacancies on sample surface. For in vitro bioactivity tests, untreated and fs-laser-treated samples were immersed in simulated body fluid for 2 weeks. Evidence of hydroxyapatite deposition on both untreated Ti-alloy, as well as, fs-laser-treated Ti-alloy surfaces after in vitro tests were provided by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), GIXRD, Fourier transform infrared spectroscopy (FTIR), and micro-Raman spectroscopy. Superior growth of HAP was observed on fs-laser-modified Ti-alloy surface in comparison with untreated surface. Biocompatibility of the laser-treated Ti-alloy was investigated by studying anchoring and growth of human osteosarcoma cell line (U2OS) on it. Using MTT assay technique in vitro cell viability and growth potential in the presence of untreated and laser-treated Ti-alloy samples were assessed. MTT test results demonstrated that, neither cell viability, nor growth were affected in the presence of either the untreated or laser-treated sample surfaces. In addition, in comparison with the untreated Ti-alloy surface, the fs-laser-treated Ti-alloy surface showed more efficient cellular attachment when examined under confocal microscope.
关键词： Biocompatibility,Hydroxyapatite,Surface modification,Ti6Al4V alloy,Femtosecond laser,Bioactivity
更新于2025-11-21 11:08:12
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Micropatterning MoS2/Polyamide Electrospun Nanofibrous Membranes Using Femtosecond Laser Pulses
摘要： The capability of modifying and patterning the surface of polymer and composite materials is of high significance for various biomedical and electronics applications. For example, the use of femtosecond (fs) laser ablation for micropatterning electrospun nanofiber scaffolds can be successfully employed to fabricate complex polymeric biomedical devices, including scaffolds. Here we investigated fs-laser ablation as a flexible and convenient method for micropatterning polyamide (PA6) electrospun nanofibers that were modified with molybdenum disulfide (MoS2). We studied the influence of the laser pulse energy and scanning speed on the topography of electrospun composite nanofibers, as well as the irradiated areas via scanning electron microscopy and spectroscopic techniques. The results showed that using the optimal fs-laser parameters, micropores were formed on the electrospun nanofibrous membranes with size scale control, while the nature of the nanofibers was preserved. MoS2-modified PA6 nanofibrous membranes showed good photoluminescence properties, even after fs-laser microstructuring. The results presented here demonstrated potential application in optoelectronic devices. In addition, the application of this technique has a great deal of potential in the biomedical field, such as in tissue engineering.
关键词： femtosecond laser,micromachining,composite nanofibers,electrospinning,MoS2
更新于2025-11-21 11:08:12
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Tailored focal beam shaping and its application in laser material processing
摘要： Besides the optimization of the laser and processing parameters, the adaptation of the focal intensity distribution offers great potential for a well-defined control of laser processing and for improving the processing results. In this paper, different tailored intensity distributions were discussed with respect to their suitability for femtosecond laser material processing on the micro- and nanoscale such as cutting, marking, and the generation of laser-induced periodic surface structures. It was shown by means of laser processing of stainless steel that the numerical simulations for the beam shaping unit are in good agreement with the experimental results. Also, the suitability of the beam shaping device to work with a scanner and an F-theta lens as commonly used for material processing was demonstrated. In this context, the improvement of the machining results was shown experimentally, and a significant reduction of the machining time was achieved.
关键词： laser-induced periodic surface structures,donut,femtosecond laser processing,top-hat,beam shaping
更新于2025-11-21 11:01:37
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Reconfigurable Near-field Enhancement with Hybrid Metal-Dielectric Oligomers
摘要： Tailoring of the near-field properties of the nanostructures is a significant task for the control of radiation of nanoscale light sources as well as for sensing applications. Generally, this task is solved in plasmonic oligomers on the fabrication step by the choice of geometry or by controlling the excitation light during the experiments. Here, the pronounced modification of the near-field pattern in hybrid gold-silicon oligomers by femtosecond laser reshaping by visualizing it with aperture-type near-field optical microscope is demonstrated. This effect correlates with a moderate red-shift of the broadband magnetic dipole resonance of the structure that occurs upon reshaping the gold component of the oligomers. The proposed all-optical near-field reconfiguration approach makes hybrid oligomers a promising platform for on-demand engineering of local field enhancement in metadevices for data recording and sensing.
关键词： near-field tuning,metal-dielectric oligomers,femtosecond laser reconfiguration
更新于2025-09-23 15:23:52
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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
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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
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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
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Live E. coli bacteria label-free sensing using a microcavity in-line Mach-Zehnder interferometer
摘要： The paper presents the first study to date on selective label-free biosensing with a microcavity in-line Mach-Zehnder interferometer induced in an optical fiber. The sensing structures were fabricated in a single-mode fiber by femtosecond laser micromachining. In contrast to other studies of this sensing scheme, where only the sensitivity to refractive index changes in the cavity was investigated, this research used chemical surface treatment of the sensor to ensure detection specificity. Immobilized MS2 bacteriophages were applied as recognition elements specifically targeting live E. coli C3000 bacteria. It is shown that the sensor allows for real-time monitoring of biological phenomena taking place on the surface of the microcavity. The developed biosensor exhibits ultrahigh refractive index sensitivity of 15,000 nm/RIU and is capable of detecting live E. coli bacteria concentrations as low as 100 colony forming units (CFU)/mL in liquid volume as low as picoliters.
关键词： label-free biosensing,E. coli C3000 bacteria,refractive index sensitivity,MS2 bacteriophages,femtosecond laser micromachining,microcavity in-line Mach-Zehnder interferometer,optical fiber
更新于2025-09-23 15:21:21