Femtosecond Pulsed Laser Ablation Research Articles

Notch effect on the linear elastic fracture mechanics values of a polysulfone thermoplastic polymer

Users of the most popular procedures for determining the linear elastic fracture mechanics parameters on polymers have noted that the repeatability and reproducibility of the results depend strongly on the quality of the notches generated. In an attempt to provide a better understanding, polysulfone specimens were pre-cracked using classical razor blade methods (tapping and sliding), and also by the femtosecond pulsed laser ablation technique. These specimens were analyzed, and the critical stress intensity factor was determined. The ablated specimens showed very good notch quality, the sharpest crack tip radii, displayed neither mechanical nor thermal damage in front of the crack tip, and were very consistent, providing both a lesser scatter and a statistically significant lower critical stress intensity factor than the razor blade pre-cracked specimens. Finally, some consideration and advice for suitable generation of notches are also given.

Mechanical modeling of metal thin films on elastomers for femtosecond laser patterned interconnects

In this work, we present the mechanical analysis of thin Au/Ti film deposited on elastomer substrate, e.g. Polydimethylsiloxane (PDMS) comparing to samples on Kapton®. After deposition, the metal was patterned by ultrashort (270 femtosecond) pulse laser ablation. Minimizing the thermal damage to the substrate, reducing Heat Affected Zone (HAZ) compared to previously demonstrated laser patterning with longer pulses. One of the major issues in the metallization of thick elastomers is the formation of wrinkles followed by brittle cracks in the metallic thin film during the process, deteriorating the metal lines performance and reliability. Such cracking has not been observed on polyimide. The crack formation was investigated using stress analysis of the metallic-elastomeric system, assuming that cracking appears when the stress in the metal film is exceeding a critical value. A general mechanical model and analysis of a multilayer and multi-material laminated system is presented and applied to the specific case of Au/Ti on PDMS. Using this model, the root cause for the stress development in the metallic film has been investigated.A series of samples had been prepared using various elastomer substrates made of Sylgard 184, Dow Corning PDMS. A series of samples was prepared using different monomer/cross-linker ratios in the range of 1:2 to 1:19 monomer to cross-linker weight percentage ratio. Using the thin film stress analysis, the inner stress between and inside the different layers was calculated. Based on the calculations, we could estimate the specific stress in the metallic film. Using this value, we could choose the right specific materials that would not surpass their critical failure stress. This hypothesis was tested and verified by the failure analysis conducted by optical microscope and scanning electrons microscopy (SEM) secondary electrons (SE) images. We report here on a good correlation between the mechanical analysis predictions and the various samples integrity. Therefore, using that model, we could define a “safe zone”, i.e. for what elastic modulus and Coefficient of Thermal Expansion (CTE) there are no “mud-crack” defects.

Compact Beam Homogenizer Module with Laser-Fabricated Lens-Arrays

We report on manufacturing of a compact beam homogenizer module including two lens arrays and an aperture. Lens arrays are fabricated by an all laser-based technology employing a precise femtosecond pulsed laser ablation and a CO2 laser polishing step. Each lens array is processed revealing a high contour accuracy and a roughness of 25 nm. The 8x8 lens arrays are designed to have a square footprint to generate a quadratic Top-Hat beam profile and focal length of 10 mm to realize compact packaging. Firstly, the lens arrays are tested in an experimental setup using commercial lens holders with their functionality being demonstrated by shaping a uniform 4.5 mm squared Top-Hat beam profile, as being calculated. Afterwards, a 3D printer is used to additively manufacture the housing for the beam homogenizer module having a length of only 16 mm. After assembling the laser-fabricated lens arrays and a laser-cutted aperture into the housing, the functionality of the miniaturized module is proven.

Femtosecond Pulse Ablation Assisted Mg-ZnO Nanoparticles for UV-Only Emission.

The need for improved UV emitting luminescent materials underscored by applications in optical communications, sterilization and medical technologies is often addressed by wide bandgap semiconducting oxides. Among these, the Mg-doped ZnO system is of particular interest as it offers the opportunity to tune the UV emission by engineering its bandgap via doping control. However, both the doped system and its pristine congener, ZnO, suffer from being highly prone to parasitic defect level emissions, compromising their efficiency as light emitters in the ultraviolet region. Here, employing the process of femtosecond pulsed laser ablation in a liquid (fs-PLAL), we demonstrate the systematic control of enhanced UV-only emission in Mg-doped ZnO nanoparticles using both photoluminescence and cathodoluminescence spectroscopies. The ratio of luminescence intensities corresponding to near band edge emission to defect level emission was found to be six-times higher in Mg-doped ZnO nanoparticles as compared to pristine ZnO. Insights from UV-visible absorption and Raman analysis also reaffirm this defect suppression. This work provides a simple and effective single-step methodology to achieve UV-emission and mitigation of defect emissions in the Mg-doped ZnO system. This is a significant step forward in its deployment for UV emitting optoelectronic devices.

PL Tunable GaN Nanoparticles Synthesis through Femtosecond Pulsed Laser Ablation in Different Environments.

The tunable photoluminescence (PL) property is very important for gallium nitride (GaN) nanoparticles in the application of ultraviolet and blue optoelectronic devices, while conventional methods are not so satisfactory that alternative methods for preparing GaN nanoparticles should be studied. In this paper, ultra-small and well dispersed GaN nanoparticles are fabricated through femtosecond pulse laser ablation in air, water and ethanol. For the PL spectra of GaN nanoparticles, there are no shifts in air, red shifts in water and blue shifts in ethanol compared with the intrinsic PL spectra of bulk GaN. The X-ray photoelectron spectroscopy (XPS) results demonstrate that the various PL spectra can be due to the different components inside the GaN nanoparticles, which not only have effect on the PL emissions, but also greatly influence the intensity of PL. This study validates that the ablation environment has a great adjustable effect on the properties of GaN nanoparticles.

Fabrication and characterization of GaAs nanoparticles achieved using femtosecond laser ablation

GaAs Nanoparticles (NPs) were produced using femtosecond pulsed laser (∼50 fs, 1 kHz repetition rate, 800 nm) ablation of bulk GaAs in distilled water. Effect of different laser energies such as 100 μJ, 200 μJ, and 500 μJ on the produced NPs was investigated. The produced NPs possessed size distribution in the range of 10–200 nm, most of the particles having an average particle size around 57 nm. In addition, nanoflake like structures having amorphous nature were also observed. With an increase in laser energy it was observed that there was a slight increase in the NPs size. For ablation performed at an energy of 500 μJ, a clear colour change (yellowish) of solution was observed due the increase in the efficiency of ablation, which could be due to a higher concentration of the NPs. Optical properties of these nanoparticles depict the absorption in the range of 264–274 nm and emission in the range of 410–440 nm. The longitudinal optical phonon-plasmon coupled (LOPC) and longitudinal optic (LO) modes observed near 266 cm−1 and 288 cm−1 in the Raman spectrum confirmed the presence of GaAs. The small shift observed in the Raman modes of GaAs NPs may be due the stress formed during the ablation. The X-ray diffraction studies revealed that the produced nanoparticles possessed cubic zinc blende structure of the GaAs.

Femtosecond laser pulse ablation characteristics of polymer-derived SiAlCN ceramics

Polymer-derived ceramics (PDCs) are promising high-performance materials for various applications, yet their brittleness represents major drawback in their machining. Femtosecond laser pulse ablation is non-contact rapid processing method used in precision machining of PDCs. Herein, two laser parameters (laser energy fluence and rotational speed) were investigated to achieve laser–material interactions and machining characteristics via machine single circular lines, blind holes, and through-holes in polymer-derived SiAlCN ceramics. With the decrease in rotational speed, the morphology of single circular lines gradually roughened and heat-affected zone was produced. Varying ablation rates were obtained at different energy fluences. For blind holes, three different ablation regions were observed. As the energy fluence increased, blind holes gradually transformed into through-holes. Through-holes with near-cylindrical profiles and minimal collateral damage were obtained. Ablation debris deposited around through-holes were indicative of N release, breaking of Si–N and C–C bonds, and formation of SiOx. Laser ablation of PDCs led to the formation of laser-induced surface structures, bubble pits, stripe structures, molten materials, and sphere-like particles.

Synthesis of multi-color luminescent ZnO nanoparticles by ultra-short pulsed laser ablation

Crystalline ZnO nanoparticles (NPs) are synthesized by ultra-short femtosecond (fs) pulsed laser ablation (PLA) of a zinc plate in deionized water, and are investigated by optical absorption and time resolved luminescence spectra in combination with the morphology and structure analysis. The comparison with previous experiments based on short nanosecond (ns) PLA highlights that pulse duration is a crucial parameter to determine the size and the optical properties of ZnO NPs. While short PLA generates NPs with average size S‾ of ~30 nm, ultrashort PLA allows to achieve much smaller NPs, S‾⩽10 nm, that evidence weak quantum confinement effects on both the absorption edge and the UV excitonic emission. Moreover, the defective nature of synthesized ZnO NPs gives rise to two visible photoluminescence bands: the first, centered around 2.3 eV and commonly associated with oxygen vacancies, unexpectedly blue-shifts on decreasing the NPs size; the second, peaked at 2.8 eV, shows a Lorentzian shape characteristic of a mobile exciton. Overall, these results demonstrate that PLA is a successful method to synthesize ZnO NPs with controlled luminescence properties, thus increasing their application in lighting technologies.

Femtosecond laser ablation-assisted synthesis of silver nanoparticles in organic and inorganic liquids medium and their antibacterial efficiency

Laser ablation from a solid target assists the synthesis of nanoparticles (NPs) as an alternative physical process. This work is attempt to investigate the morphological properties of silver nanoparticles (AgNPs) synthesized by femtosecond pulsed laser ablation in different liquid medium; Double Distilled Water (DDW), Deionized Water (DIW), Tetrahydrofuran (THF), and Dimethylformamide (DMF). XRD diffraction peaks that corresponds to (111), (200), (220) and (311) planes confirm the synthesized of AgNPs. The absorption spectra confirm the existence surface plasmon resonance (SPR) peak of AgNPs. The direct optical energy band gap (Eg) values have been calculated according to Tauc's equation and equal to 3.97, 3.82, 3.86, and 3.88 eV for synthesized AgNPs by Fs PLAL at different medium; DDW, DIW, THF, and DMF, respectively. Also, the influence of different liquid medium on the antibacterial efficiency was studied. In vitro Antibacterial activity of synthesized AgNPs was carried out against four types of bacteria employing agar plate technique. The experiments demonstrated that ablation efficiency, stability, and antibacterial efficiency of AgNPs in DIW medium are higher than those prepared in DDW, THF, and DMF medium.

Production of fluorescent nano-diamonds through femtosecond pulsed laser ablation

A one-step method for synthesizing nano-diamonds (NDs), femtosecond pulsed laser ablation, of bulk diamond in DI water is reported. The mean size of NDs is 3.0 nm observed by TEM. UV-Vis absorption spectrum reveals that there are two absorption peaks in NDs. For prepared NDs, it can be seen from emission spectrum that dual emission occurs under the excitation of either 260 nm or 280 nm, while the dual emission disappears after surface passivation. Moreover, the intensity of visible blue fluorescence emitted by NDs is significantly enhanced for passivated NDs. In addition, it is found that the ablation efficiency enhances with the increase of ablation power, which can be also verified by the intensity changing of UV-Vis absorption spectra. The maximum yield can reach to 8.2 mg·h−1 under 828 mW. These NDs emit stable blue emission and are synthesized by a rather simple green way, of which the NDs yield can meet the requirement of practical applications in terms of drug and gene delivery.

Femtosecond Laser Pulse Ablation of Sub-Cellular Drusen-Like Deposits

Age-related macular degeneration (AMD) is a condition affecting the retina and is the leading cause of vision loss. Dry AMD is caused by the accumulation of lipid deposits called drusen, which form under the retina. This work demonstrates, for the first time, the removal of drusen-like deposits underneath ARPE-19 cell layers using femtosecond laser pulses. A novel cell culture model was created in response to the limited access to primary cell lines and the absence of animal models that recapitulate all aspects of AMD. In the cell culture model, deposits were identified with fluorescent stains specific to known deposit constituents. Trains of sub-10 femtosecond laser pulses from a Ti:Sapphire laser were used to successfully ablate the deposits without causing damage to surrounding cells. This drusen removal method can be used as a potential treatment for dry-stage AMD.

A new nanocomposite based on LASiS-generated CuNPs as a preservation system for fruit salads

Abstract In this work, nanocomposites based on polyethylene oxide (PEO) and copper nanoparticles (CuNPs) for food packaging application were developed as new active packaging for fresh foodstuffs. Copper colloids were synthesized by femtosecond-pulsed laser ablation synthesis in solution (LASiS) using an organic environment, to ensure a good solubility of nanocolloids in polymeric solution. CuNPs were incorporated in a biodegradable polymer matrix for the preparation of composite films. Besides a deep morphological and spectroscopic characterization, bioactive ions release over time from composite thin films was studied by atomic absorption spectroscopy. Finally, in vivo tests on fresh-cut fruit were carried out to assess the effects of these nanocomposite systems on product quality. CuNPs-PEO composites were found effective to prevent quality decay of fruit salad. In particular, the active films allowed better preserving color and texture of fruit that remained acceptable for 3–4 days more than the control sample.

3D quantum theranosomes: a new direction for label-free theranostics.

Quantum-scale materials offer great potential in the field of cancer theranostics. At present, quantum materials are severely limited due to 0D & 1D materials lacking biocompatibility, resulting in coated materials with labelled tags for fluorescence excitation. In addition, the application of magnetic quantum materials has not been reported to date for cancer theranostics. In this current research study, we introduce the concept of applying nickel-based magnetic 3D quantum theranosomes for label-free broadband fluorescence enhancement and cancer therapy. To begin with, we present two (primary and secondary) distinct quantum theranosomes for cancer detection and differentiation (HeLa & MDAMB-231) from mammalian fibroblast cells. The primary theranosomes exhibit a metal enhanced fluorescence (MEF) property through localized surface plasmon resonance to act as cancer detectors, whereas the secondary theranosomes act as cancer differentiators through the fluorescence quenching of HeLa cancer cells. Apart from the above, the synthesized magnetic quantum theranosomes introduced therapeutic functionality wherein the theranosomes mimicked a tumor microenvironment by selectively accelerating the proliferation of mammalian fibroblasts cells while at the same time inducing cancer therapy. These quantum theranosomes were synthesized using femtosecond pulse laser ablation and self-assembled to form an interconnected 3D structure. The 3D architecture and the physicochemical properties of the laser synthesized quantum theranosomes closely resembled a tumor microenvironment. Furthermore, we anticipate that our current recorded findings can shed further light upon these unique magnetic quantum theranosomes as potential contenders towards opening an entirely new direction in the field of cancer theranostics.

Computer modelling of pulsed laser femtosecond ablation for metals

In this article a mathematical model for a femtosecond pulsed laser ablation for metals is proposed. This model is based on two-temperature model for electrons and ions with addition of hydrodynamic part and wide-range semi-empirical equation of state for metals. The results of the modelling for several metals are compared with experimental data at different laser fluence and duration of pulses for ablation depth. A good agreement with them and the experiment is received.

Computer simulation of femtosecond pulsed laser ablation of aluminium and copper

In this paper a mathematical model for laser ablation of metals by femtosecond laser pulses is developed, based on two-temperature model with hydrodynamic equations and wide-range equation of state for metals. The simulation results for aluminium and copper are compared with experimental data for ablation depth at different laser fluence and duration of pulses. A good agreement for both metals with the results of simulation and the experiment is received

Electron Microscopy and X-Ray Diffraction Analysis of Titanium Oxide Nanoparticles Synthesized by Pulsed Laser Ablation in Liquid

A femto-second pulsed laser ablation in liquid (PLAL) procedure for the generation of titanium oxide nanoparticles (NP) is reported with the purpose of understanding morphology and structure of the newly generated NPs. Ablation duration was varied for optimization of NP generation processes between 10 and 90 min. Surface morphology of NPs as well as their size and shape (distribution) were analysed by various complementary electron microscopy techniques, i.e. SEM, TSEM and TEM. The crystalline structure of titanium oxide particles was investigated by XRD and HR-TEM. Concentration of generated titanium oxide NPs in liquid was analysed by ICP-MS. A mix of crystalline (mainly anatase), partly crystalline and amorphous spherical titanium oxide NPs can be reported having a mean size between 10 and 20 nm, which is rather independent of the laser ablation (LA) duration. A second component consisting of irregularly shaped, but crystalline titanium oxide nanostructures is co-generated in the LA water, with more pronounced occurrence at longer LA times. The provenance of this component is assigned to those spherical particles generated in suspension and passing through the converging laser beam, being hence subject to secondary irradiation effects, e. g. fragmentation.

Ultra-short-pulse laser ablation and modification of fully sprayed single walled carbon nanotube networks

In this study, we report on femtosecond (470fs) laser pulse ablation and modification of solution processed single-walled carbon nanotube (SWCNT) networks sprayed on oxidized silicon and polyimide substrates. Taking advantage of the small heat affected zone of the femtosecond pulse regime we demonstrate precise and selective laser processes, that advance laser patterning beyond simple galvanic isolation. A thorough investigation regarding the laser pulse-SWCNT film interaction is performed, identifying critical interaction regimes in the single- and multi-pulse operation mode. For the first time we achieve a pronounced debundling of the network, by operating the laser below the ablation threshold, a process that was previously limited to pre-deposition. Furthermore, we investigate the effect of polarized laser pulses on the ablation properties. Making use of linear polarized laser pulses we are able to selectively ablate SWCNTs, which are oriented parallel to the incident laser polarization, resulting in aligned networks with anisotropic conductivity. This feature was previously tied to direct growth of SWCNTs, strongly limiting its implementation. The scaleability of the presented femtosecond laser processes is demonstrated, allowing for the use of low-cost solution processed SWCNT thin-films, while maintaining the advantages of on-chip SWCNT growth such as SWCNT separation and alignment.

Radiation characterisation and dosimetric measurements of a femtosecond pulsed laser ablation system

This work describes the radiation characterisation and dosimetric measurements performed on the low-energy micromachining station of the femtosecond STELA (Santiago TErawatt LAser) at the University of Santiago de Compostela (Spain). For this aim, ionisation chambers, solid state detectors, and radiochromic films were used. The results show the emission of pulsed x-ray produced by laser-accelerated electrons from the ablated material exhibiting both bremsstrahlung and characteristic radiation. Although this radiation was produced unintentionally, a high superficial dose rate can be achieved. This radiation can be successfully stopped using small shielding to protect personnel from its effects. Based on the results of this work, the yearly dose equivalent after installing the shielding was negligible.

Morphology and structure of TixOy nanoparticles generated by femtosecond laser ablation in water

In this work femto-second pulsed laser ablation in liquid (PLAL) procedure for the generation of titanium oxide nanoparticles (NP) is reported with the purpose of understanding morphology and structure of the newly generated NPs. Ablation duration was varied for optimization of NP generation processes between 10 and 90 min. Surface morphology of NPs as well as their size and shape (distribution) were analysed by various complementary electron microscopy techniques, i.e. SEM, TSEM and TEM. The crystalline structure of titanium oxide particles was investigated by XRD (two instruments operated in different geometries) and HR-TEM. Concentration of generated titanium oxide NPs in liquid was analysed by ICP-MS. A mix of crystalline (mainly anatase), partly crystalline and amorphous spherical titanium oxide NPs can be reported having a mean size between 10 and 20 nm, which is rather independent of the laser ablation (LA) duration. A second component consisting of irregularly shaped, but crystalline titanium oxide nanostructures is co-generated in the LA water, with more pronounced occurrence at longer LA times. The provenance of this component is assigned to those spherical particles generated in suspension and passing through the converging laser beam, being hence subject to secondary irradiation effects, e. g. fragmentation.

Notch effect on the fracture of a polymeric film

The fracture behavior of a bio-based thermoplastic copolyester film has been studied by combining the essential work of fracture, the J-integral, and the crack tip opening displacement characterization methods on double edge notched tension specimens, in an attempt to provide a better understanding of the details that play an important role in the repeatability and the reproducibility of the essential work of fracture test, with particular attention to the effect of the quality of the notches generated by two different notch sharpening techniques. Specifically, the femtosecond pulsed laser ablation and the classic razor blade sliding techniques have been applied. The equivalence, reported and discussed in the literature, between the specific essential work of fracture and the J value at crack initiation, as well as their relationship with the crack tip opening displacement, have been confirmed. It is also identified the parabolic shape of the stress-displacement curves, which modeled relates the specific non-essential work of fracture with the stress at initiation and the extension ratio during the crack growth.