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Characterization and laser-induced degradation of a medical grade polylactide
摘要： In this study, we carried out the structural and thermal characterization of a medical-grade poly (lactide) (PLA) by SEC, TGA, DSC, NMR, ICP-MS and Py-GC/MS. Moreover, we investigated the laser-induced degradation occurring when ultrashort laser pulses (ULP) were employed to cut extremely thin polymer films prepared by solvent-casting. ULP polymer cutting technology is an interesting manufacturing process for its advantages in potential medical applications. In fact, heat transmission to the region surrounding the cuts is limited, so that the incisions are precise and the effects on the regions around them are small. In this way, the need for post-processing is reduced and ULP cutting becomes interesting for industrial applications. However, degradation induced by ULP may occur and compromise the properties of the polymer samples. To investigate this possibility, portions of PLA films, ultrashort laser cut (ULC) and uncut, were analysed by SEC, DSC, NMR and FTIR. Furthermore, PLA oligomers were studied by ESI-MS. Both SEC and NMR showed a decrease in the molecular weight. FTIR, ESI-MS and NMR spectra revealed the presence of olefin end groups originated from a b-H transfer mechanism, induced by heat and/or light (Norrish II mechanism). Additionally, the inspection of the ESI mass spectra highlighted the cleavage of ester bonds related to the Norrish I type mechanism, undetected by the other techniques.
关键词： Polymer degradation,Ultrafast laser sources,Norrish mechanisms,Biodegradable polymers,Polylactide,Micro-cutting
更新于2025-09-11 14:15:04
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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) - Diamond Functionalization by Ultrafast Laser Pulses
摘要： The extreme material properties of diamond make it an attractive candidate for many technological applications. However, these same material properties often prove disruptive to the machining of diamond into functional devices. Ultrashort laser pulses focused inside diamond offer a potential new route for the functionalisation of diamond, offering a range of fabrication modalities on a single platform. Focusing beneath the surface of diamond, there is sufficient intensity from ultrashort laser pulses for non-linear absorption of light, which can lead to modification of the diamond lattice. The non-linearity of the process confines the modification to the focal volume of the laser, without effecting the diamond surface or surrounding regions. At high pulse energies (above ~100nJ), the laser deposits sufficient energy to break down the diamond lattice and induce a graphitic phase. Tracing the diamond through the laser focus allows the creation of conductive graphitic wires embedded inside the diamond in 3D. The processing becomes deterministic and the wire conductivity increases when the fabrication is carried out at high numerical apertures (NA = 1.4) [1]. The large refractive index mismatch at the diamond surface generates a depth dependent spherical aberration which should be corrected using adaptive optics. The laser written electrical wires can be used to fabricate radiation sensors, as shown in Fig. 1(a), which benefit from the radiation hardness of diamond. The advances in laser fabrication allow the realisation of new detector geometries. The graphitic inclusions fabricated by ultrashort pulse lasers beneath the surface of diamond exert stress on the surrounding diamond, which in turn modifies the optical properties of the crystal. By designing stress fields, it is possible to fabricate optical waveguides [2] and waveguide Bragg gratings [3] inside the diamond. In a different fabrication regime, it is also possible functionalise the diamond using ultrashort pulses without causing breakdown of the diamond lattice. We have shown that with a single ultrashort pulse it is possible to generate an ensemble of vacancies at the laser focus inside the diamond. A thermal anneal process heals any damage to the lattice and is successful in forming highly coherent isolated single nitrogen vacancy (NV) colour centres [4, 5]. We have recently demonstrated improvements to the method using a laser based localised anneal with fluorescence feedback to write arrays of NV centres with near unity yield and in-plane positioning accuracy of 40nm [6].
关键词： functionalisation,diamond,graphitic wires,ultrafast laser pulses,NV centres,optical waveguides
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Miramar Beach, FL, USA (2019.8.19-2019.8.21)] 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Mid-IR Ultrafast Laser Inscribed Waveguides and Devices
摘要： Ultrafast laser inscription (ULI) is a highly versatile technique for creating index modifications in glasses and crystalline materials. The process of ULI relies on ultrashort laser pulses focused inside of a material. The high intensity of the pulsed beam induces nonlinear absorption processes, which transfers the pulse energy to the material lattice. With careful experimental control of the laser parameters, a permanent change in the refractive can be obtained in the bulk material. The permanent refractive index change obtained by ULI can be used to create waveguides and devices in active and passive materials. In this work, we present recent advances on creation of guided wave devices in Mid-IR compatable materials such as Fe:ZnSe, Cr:ZnSe, Ho:YAG, LiNbO3, and CdSiP2.
关键词： Ultrafast Laser Inscription,Solid-state lasers,Infrared Lasers
更新于2025-09-11 14:15:04
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Microwelding of glass to silicon by green ultrafast laser pulses
摘要： In the present work, a direct bond between glass and silicon with optical contact was formed by 515 nm picosecond laser controlled by the galvanometer scanning system. A crack-free welding effect without edge breakage and residues was obtained with breaking strength as high as 122 MPa. New crystalline phase (SiO2) was produced and silicon and oxygen have a spatial distribution gradient in the welding area analyzed by XRD and EDS, respectively, revealing that mixing and inter-diffusion of substances have occurred during laser irradiation. The transmission of near infrared light in the welding area is significantly increased compared with the non-welding area analyzed by inverted microscope. A confocal laser scanning microscope was used to observe the morphology and width of welds, which variation trend of axial focal positions is consistent with the teardrop structure produced by nonlinear absorption effect. Scanning speeds and laser repetition frequencies also affect the width and morphology of the weld.
关键词： Silicon,Glass,Microwelding,Ultrafast laser
更新于2025-09-11 14:15:04
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Optimization of ultrafast laser parameters for 3D micromachining of fused silica
摘要： We present an optimization study on laser parameters for 3D micromachining of fused silica to achieve critical goals for practical applications including high surface quality, high volume production, and complex surfaces by ultrafast laser direct writing assisted chemical etching. We conducted experiments on laser pulse width of 300 fs and 1 ps, pulse energy ranging from 0.1 μJ to 1.6 μJ, three different polarizations (circular, parallel and perpendicular) and number of overlapped pulses from 3 to 10,000 at 1030 nm with up to 2 MHz repetition rate to investigate their effect on nanogratings and one dimensional (1D) channel and two dimensional (2D) planar surface selective etching on 1 mm thick fused silica. In one configuration, we achieved 21.8 nm RMS surface roughness with 80 μm Gaussian filtering and in another configuration, we estimated the maximum writing speed to be 1.25 m/s for given 2 MHz repetition rate with less than 400 nm filtered root mean square (RMS) surface roughness at a 1 mm2 area which covers the thickness of the glass.
关键词： 3D microfabrication,Direct writing,Roughness,Chemical etching,Selectivity,Ultrafast laser
更新于2025-09-11 14:15:04
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Field emission microscopy pattern of a single-crystal diamond needle under ultrafast laser illumination
摘要： We report herein on the spatial beam properties of a ?eld emission electron source based on a single-crystal diamond needle illuminated by ultrashort light pulses. We show that the increasing of the laser intensity strongly modi?es the emission pattern, leading to the emergence of a new emission region at high peak power. This region is situated on the opposite side of the diamond needle to the one irradiated by the laser. By spatially-resolved energy spectrometry, we prove that the electrons emitted from this region are governed by a multi-photon absorption process. The occurrence of this emission pattern can be explained by accounting for the inhomogeneous distribution of the optical ?eld enhancement and the laser absorption induced by light diffraction within the nanometric needle. The numerical simulations performed on a real sub-wavelength tip con?rm this localization of the optical ?eld enhancement and reveal that the electrons trajectories match the spatial beam distribution evidenced experimentally. This work underlines the need to closely monitor the surface roughness of the ?eld emitter as well as the laser illumination conditions to ?nely control its emission pattern.
关键词： ?eld emission,diamond,ultrafast laser,electron spectroscopy,nanoemitters
更新于2025-09-11 14:15:04
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Light absorption by surface nanoholes and nanobumps
摘要： This paper deals with a numerical investigation of the energy deposition induced by ultrafast laser interaction with nanostructures. We calculate and analyze the intensity near-field reactive and radiative patterns resulted from the interference of the incident light with light scattered by individual subwavelength holes and bumps on the surface of metallic and dielectric materials. The role of light polarization, optical material properties, collective effects and nature of the imperfections in localized energy absorption is elucidated. The results open new perspectives in precise light manipulation by surface inhomogeneities and well-controlled surface nanostructuring by ultrashort laser.
关键词： light absorption,surface nanoholes,ultrafast laser,nanostructures,nanobumps
更新于2025-09-10 09:29:36
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Arbitrary amplitude femtosecond pulse shaping via a digital micromirror device
摘要： An ultrafast spectrum programmable femtosecond laser may enhance the performance of a wide variety of scientific applications, e.g., multi-photon imaging. In this paper, we report a digital micromirror device (DMD)-based ultrafast pulse shaper, i.e., DUPS, for femtosecond laser arbitrary amplitude shaping — the first time a programmable binary device reported to shape the amplitudes of ultrafast pulses spectrum at up to 32 kHz rate over a broad wavelength range. The DUPS is highly efficient, compact, and low cost based on the use of a DMD in combination with a transmission grating. Spatial and temporal dispersion introduced by the DUPS is compensated by a quasi-4-f setup and a grating pair, respectively. Femtosecond pulses with arbitrary spectrum shapes, including rectangular, sawtooth, triangular, double-pulse, and exponential profile, have been demonstrated in our experiments. A feedback operation process is implemented in the DUPS to ensure a robust and repeatable shaping process. The total efficiency of the DUPS for amplitude shaping is measured to be 27%.
关键词： digital micromirror device,Spectrum shaping,ultrafast laser
更新于2025-09-09 09:28:46
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Thermally-induced nonlinear spatial shaping of infrared femtosecond pulses in nematic liquid crystals
摘要： An optically-induced thermal non-linear effect in a nematic liquid-crystal (E7) cell is evidenced through weak light-absorption by the ITO coating of an infrared pulsed femtosecond laser (λ0 = 1.5 μm). Strong spatial self-phase modulation is generated, thus a multiple-ring pattern is observed in the far-field. The sign of the nonlinearity is changed depending on the laser polarization. The refractive index and thermal gradients are measured as a function of the laser intensity and we observe that the temperature can increase close to the nematic phase transition. The fidelity and stability of the process open new prospects for spatial shaping devices and delimits the operating wavelength range for ultrafast liquid-crystal based electro-optic application.
关键词： liquid crystal,spatial light modulators,ultrafast laser
更新于2025-09-09 09:28:46
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[Topics in Current Chemistry Collections] Multidimensional Time-Resolved Spectroscopy || Multidimensional Vibrational Coherence Spectroscopy
摘要： Multidimensional vibrational coherence spectroscopy has been part of laser spec-troscopy since the 1990s and its role in several areas of science has continuously been increasing. In this contribution, after introducing the principals of vibrational coherence spectroscopy (VCS), we review the three most widespread experimen-tal methods for multidimensional VCS (multi-VCS), namely femtosecond stimu-lated Raman spectroscopy, pump-impulsive vibrational spectroscopy, and pump-degenerate four wave-mixing. Focus is given to the generation and typical analysis of the respective signals in the time and spectral domains. Critical aspects of all multidimensional techniques are the challenges in the data interpretation due to the existence of several possible contributions to the observed signals or to opti-cal interferences and how to overcome the corresponding difficulties by exploiting experimental parameters including higher-order nonlinear effects. We overview how multidimensional vibrational coherence spectroscopy can assist a chemist in under-standing how molecular structural changes and eventually photochemical reactions take place. In order to illustrate the application of the techniques described in this chapter, two molecular systems are discussed in more detail in regard to the vibra-tional dynamics in the electronic excited states: (1) carotenoids as a non-reactive system and (2) stilbene derivatives as a reactive system.
关键词： Excited states,Photoisomerization,Multidimensional spectroscopy,Coherence spectroscopy,Vibronic coupling,Ultrafast laser spectroscopy,Raman,Vibrational spectroscopy
更新于2025-09-04 15:30:14