Laser produced plasma ions implantation has a great potential to change various characteristics of the polymer after irradiation, such as, surface, structural, optical and electrical properties. For this purpose, polymer CR- 39 is implanted by laser produced Ni plasma ions at various fluences ranging from 75 x 10(13) to 95 x 10(16) ions/cm(2). The ion energy estimated by Thomson parabola technique using CR-39 detectors was 540 KeV. Digital optical microscopic analysis illustrates the formation of granular morphology for all ion fluences. However, at the maximum fluence (95 x 10(16) ions/cm(2)), distinct and well organized grains with sub-granular morphology are observed. Confocal microscopic analysis shows the development of micro/nano sized caters, voids, ion tracks, clusters and bumps for various fluences of Ni ions ranging from 75 x 10(13) to 60 x 10(15) ions/cm(2). Whereas, at the maximum ion fluence (95 x 10(16) ions/cm(2)), hillock like features are observed. Raman spectroscopy analysis shows the formation of carbonaceous structures along with new bonds of Ni-C=O in implanted CR-39. Reduction in transmittance value from 92.2% to 60.8% is observed with increase in ion fluence from 75 x 10(13) to 95 x 10(16) ions/cm(2). The electrical conductivity of implanted CR-39 increases by increasing the ion fluence. Formation of conductive layer and carbonaceous structures are considered to be accountable for improvements in electrical conductivity of implanted target polymer. The observed stopping power or Linear Energy Transfer (LET) of 540 KeV Ni ions in CR-39 is 72.88 eV/angstrom ' and their corresponding depth is 686 nm.

Ion implantation of laser induced graphite plasma has been performed for modifications in surface, optical, electrical and structural properties of CR-39. KrF Excimer laser (248 nm, 18 ns, 120 mJ), at an irradiance of 2.5 x 10(8) W cm(-2) is utilized for the production of graphite plasma. The energy and fluence of graphite ions are estimated by Thomson parabola technique. The targets are implanted with energy of 710 KeV graphite ions for four fluences ranging from 26 x 10(12) to 92 x 10(15) ions/cm(2), in presence of magnetic field of strength 90 mT. The digital optical analysis reveals well-arranged dendritic and island like structure formation on irradiated polymer surface. Confocal microscopic investigation illustrates the growth of nano/micro sized craters and hillocks for various ion fluences. Dissociation of bonds along with formation of new bonds is confirmed from Raman analysis. UV-Vis spectral analysis reveals that the optical transmittance values for visible regions of CR-39 are drastically reduced from 90 % to 68 % for maximum laser fluence of 92 x 10(15) ions.cm(-2). Significant improvement in electrical conductivity is achieved from 10(-9) to 10(-7) Scm(-1) for lowest fluence value of graphite ions. SRIM software is utilized for the measurement of stopping power or Linear Energy Transfer (LTE) of 710 Kev graphite ions, is about, 55.53 eV/angstrom, in the CR-39 targets.

The present paper reports the investigation of surface morphology, elemental composition, phase changes and field emission properties of Si ion irradiated nickel (Ni) and titanium (Ti). The Ni and Ti targets have been irradiated with 500 keV Si ions generated by Pelletron accelerator at various fluences ranging from 6.9 × 1013 to 77.1 × 1013 ions/cm2. Stopping range of ions in matter analysis revealed higher values of electronic stopping and sputtering yield for Ni as compared with Ti. For both irradiated metals, electronic energy loss dominant over the nuclear stopping. The growth of induced surface structures have been analysed by using field emission scanning electron microscopy (FESEM) analysis. In case of Ni, as the ion fluence increases from 6.9 × 1013 to 65.8 × 1013 ions/cm2, the formation of spherical particulates, agglomers and sputtering is observed. Although in the case of Ti, with the increase of Si ion fluence from 11.6 × 1013 to 77.1 × 1013 ions/cm2, the formation of irregular‐shaped particulates along with crater and sputtered channels is observed. X‐ray diffraction (XRD) analysis shows that no new phase is identified. However, a significant increase in peak intensity is observed with increasing ion fluence. The variation in crystallite size and dislocation line density is also observed as a function of Si ion fluence. Fourier transform infrared spectroscopy analysis shows that no bands are formed after the Si ion irradiation. Field emission properties of ion‐structured Ni and Ti are well correlated with the growth of surface structures observed by SEM and dislocation line density evaluated by XRD analysis.

Laser-induced silicon (Si) plasma has been used as a source of ion irradiation for modifications in surface, structural and field emission properties of Stainless Steel (SS). Nd:YAG (532 nm, 10 ns) laser at irradiance of 15 GW/cm(2) was used to generate Si-plasma ions which were detected by solid-state nuclear track detector (CR-39) and Faraday Cup (FC). Both the energy and fluence of Si ions were measured by FCs. In response to a stepwise increase in the number of laser pulses from 3000 to 12000, the ion fluence varies from 4.6 x 10(14) to 18.3 x 10(14) ions/cm(2) with constant energy of 30 keV. Fourier Transformation Infrared (FTIR) spectroscopy analysis revealed that irradiated silicon makes the stretch band with oxygen Si-O-Si. X-Ray Diffraction (XRD) analysis confirmed the identification of new phase of Si (111) with an anomalous trend in crystallite size, dislocation line density and induced stresses in response to the irradiation with various Si ion fluences. Optical microscopy analysis showed the formation of pits, voids and tracks. Scanning electron microscope (SEM) analysis revealed the formation of nanoscale surface features including pores, craters, embedded particulates and protruded disk-like structures with multiple ablative layers at the fluence of 4.6 x 10(14) to 13.7 x 10(14) ions/cm(2). At the highest ion fluence of 18.3 x 10(14) ions/cm(2), the flake/flower-like morphology is observed. Field emission (FE) properties were studied under ultra-high vacuum condition in a parallel plate con?guration using planar virgin SS as an anode and structured SS as a cathode. The Fowler-Nordheim plots were obtained from I-V characteristics to evaluate the turn-on field, field enhancement factor beta and a maximum current density ranging 1.5-4.5 V/mu m, 5008-12807 and 96-454 nA/cm2, respectively. The variation in the FE properties is attributed to the different morphological features at varying silicon ion fluences.

This paper reports the effect of Ti:Sapphire laser (800 nm, 30 fs) fluence on the surface morphology, ablated area, ablation rate and hardness of a femtosecond laser irradiated Zn in air and ethanol. Targets were exposed to 1000 succeeding pulses at various fluences ranging from 1.3 to 5 J cm−2. To characterize the growth of structures on the surface of irradiated Zn, Field Emission Scanning Electron Microscopy (FESEM) has been performed. The ablation depth has been measured using a confocal microscope. Nonuniform surface morphology with an appearance of both micro and nanoscale droplets, particulates and rims has been observed in case of air-assisted ablation, whereas, in ethanol, nanoscale colloids, droplets, pores and bowl-shaped cavities have been formed. The ablation of Zn in air is responsible for deep craters with pronounced melt expulsions and ripples. Whereas, shallow and clean craters are formed in ethanol. The ablation threshold fluence is evaluated analytically and experimentally by employing three methods, i.e., squared diameter, depth ablation rate, and volume ablation rates. The hardness of irradiated targets is higher as compared to untreated Zn and shows an increasing trend with increasing fluence for both environments. However, in the case of ethanol, the hardness values are higher than air.

Development of materials with highly nonlinear optical activity represents an intensively studied discipline due to potentially unique applications of such materials in photonics and information technologies. In this work the creation of ordered nanostructured arrays of c-shaped metals (Ag, Au, Al, and Pd) and characterization of their nonlinear optical properties are described. Large scale ordered arrays were created by the excimer laser pattering of a polymer surface and subsequent coating with Ag, Au, Al, and Pd. The successful creation of required structures was confirmed by the conductive AFM and FIB-SEM techniques. Linear optical response of the structures was examined using the UV–Vis technique and strong excitation of surface plasmon polariton resulting in appearance of strong absorption band was confirmed. The Z-scan technique with femtosecond laser pulses was used to determine the nonlinear optical response of the prepared metal arrays. It was found that the strong two-photon absorption appears under the illumination at the wavelength corresponding to the surface plasmon excitation. Extensive comparison with available literature data shows that the present structures exhibit markedly higher two-photon absorption activity.

This paper reports on the effect of both the pulse duration and environments on the surface morphology, ablated area, ablation rate, and mechanical properties of a femtosecond laser irradiated zinc (Zn) in air and ethanol. The targets were exposed to 1000 succeeding pulses of Ti:sapphire laser (800 nm) at a fluence of 2.5Jcm−2 with various pulse durations ranging from 30 to 550 fs. The surface structures have been characterized by a field emission scanning electron microscope, whereas the ablation rate has been measured using confocal and optical microscopy. The mechanical behavior of irradiated targets has been explored by using a microhardness tester. It is observed that in the case of Zn ablation in air, a crater with nonuniform surface morphology along with formation of both micro- and nanoscale droplets rims, organized laser-induced periodic surfaces are observed, whereas in the case of ablation in ethanol, nano- and microscale scale droplets, pores, cones, agglomerates, and channels are formed. The growth and the shape of these structures are strongly dependent on the pulse durations and environments. The hardness of laser-treated samples is found to be higher as compared to untreated ones and is also found higher for liquid-assisted ablated Zn as compared to air-assisted ablated targets due to an increased chemical reactivity in an ethanol-confined environment. The decreasing trend of hardness with increasing pulse duration for both environments is observed, which is attributed to decreasing trend in both shock pressure and ablation pressure with increasing pulse duration.

We show spectacular and different effect of the sequential and simultaneous writing of two perpendicularly polarized ultrashort laser pulse trains on profile and magnitude of induced optical retardation inside fused silica glass. Clear birefringence was observed in the region exposed to linearly polarized pulse train radiation. It found out that the induced birefringence is erasable. It means that, when the sample is irradiated again with pulse train having perpendicular polarization, the induced birefringence is vanished and can be totally erased by optimizing the pulse energy. However, in a simultaneous writing approach, a contradictory result was observed. When the glass substrates were simultaneously (i.e. with an accuracy better than the pulse duration) exposed to two beams with perpendicular polarization the induced birefringence not only remained but also enhanced. Discussion and study on the results of interaction of polarized single ultrashort laser pulse and sequential laser beams (which spatially overlapped) having different polarizations and also change of energy ratio of simultaneously writing pulse trains helps us to analyze different results of the simultaneous interaction of two orthogonally polarized ultrashort laser pulse trains with transparent material. Our results provide pieces of evidence for further understanding the physical mechanism of creation of the birefringence using ultrashort laser pulses. Additionally, they provide the ability to manipulate the transient electron dynamics to control the profile and tailor of the induced birefringence.

Direct femtosecond laser ablation enables the maskless fabrication of nano- and micro-scale structures on variety of materials. A typical example is the formation of femtosecond Laser Induced Periodic Surface Structures (fs-LIPSSs), which can lead to strong modification in electrical, optical, wetting, and field emission properties of materials. Here, we study the field emission properties of fs-LIPSSs. We created fs-LIPSSs and fs-LIPSSs covered with nano- and micro-scale structures at different laser fluences on Tungsten (W) and showed that these structures offer significant enhancement in electron field emission properties. We provide a phenomenological model to explain the enhancement of electron emission parameters. The enhancement in the field emission properties of laser irradiated W is explained based on the convergence of electric field lines at the ridges of the fs-LIPSSs and fs-LIPSSs covered with nanoscale structures, which in turn, enhances the local field intensity and the electron emission parameters. The direct fabrication of 1D subwavelength structures is an important step towards the creation of low-cost cathodes for various potential applications.

TPA is known to be a highly sensitive process. Open aperture Z-scan technique has been employed to measure two photon absorption cross section (TPCS) of Rhodamine B and Rhodamine 6G solutions in MeOH. An in depth analysis is carried out to assess the influence of medium as well as laser parameters on TPCS and relative TPA trends. The explored laser parameters are laser energy and pulse width. The varying medium parameters are dye solution concentrations and sample length (cuvette size). True value of TPCS is found to be independent of change in laser energy and pulse width (laser intensity). However, relative TPA is enhanced by increasing pulse energy due to increased transition probability. Shorter pulse width resulted in reduced TPA due to saturation effects. Increase in solution concentration has decreased TPCS due to agglomeration effects. An increase in TPCS with increased sample length is observed owing to an overall increase in TPA absorbers.

We present an experimental technique to determine the degenerate two-photon absorption (2PA) spectra by performing a single Z-scan using a high-spectral-irradiance white light continuum (WLC) generated by a hollow core fiber. The hollow fiber was filled with Argon (Ar) gas at a pressure of 0.6 bar and was pumped with 500 mJ, 30 fs, and 800 nm pulses. The broadband WLC pulses with 350 nm bandwidth in the range of 600–950 nm were compressed to sub-8 fs pulses. To characterize and interpret the data obtained from this method, the spectral, temporal and spatial characteristics of the WLC were first analyzed. The WLC emerging from the compressor was dispersed using a prism pair and then focused into the sample by a cylindrical lens. Since different spectral components are spatially separated, any part of the sample in the beam cross section is irradiated with almost single wavelength pulses leading to only a degenerate 2PA process. The nonlinear transmittance was then measured by a charge-coupled-device (CCD) line camera as a function of the sample position while the sample was moved along the beam direction by a motorized translation stage. In this way the Z-scans at different wavelengths in the WLC spectral range can be measured and thus the wavelength-resolved degenerate 2PA spectra can be obtained by performing a single scan using dispersive WLC. This method was verified on a well-characterized dye Rhodamine B and yield a reasonable agreement with the data found in the literature. We used this method to determine the 2PA spectra of some two-photon initiators (2PIs) developed for two-photon polymerization (2PP) based 3D micro-structuring.

Aluminum (Al) samples were irradiated with femtosecond (fs) laser pulses for different laser fluences under two different environments of vacuum & Oxygen (O-2). Nano/Micro structures on the surface of irradiated Al were explored by using Scanning Electron Microscope (SEM). Self-organized patterns like ripples, cellular structures, cluster of particles and cavities are observed by SEM analysis. Single and multiple (100) shot, ablation threshold value and incubation coefficient were also calculated by means of SEM images, under both ambient conditions i.e. vacuum and O-2 environments. While the comparison for single and multiple (100) shots shows a decrease in the value of ablation threshold with increase of number of laser pulses due to presence of incubation effect. X-ray Diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDX) analysis were utilized for identification of phases and the chemical composition of ablated targets, respectively. A variation in Al content as well as in peak intensities of almost all phases is observed under vacuum treatment. In case of treatment in O-2 ambient, oxides of Al are achieved with significantly enhanced concentration of O-2. After ablation under vacuum condition reduction in atomic O content (already present on un-ablated target) is observed. The reduced ablation threshold of metals makes the laser material processing mechanisms like cutting, drilling, welding and surface modifications, more effective. The observed reduced ablation threshold of Al in O-2 as compared to vacuum, as well as oxidation of Al along with the growth of surface structures make this metal more useful for various industrial as well as scientific applications. Nano-hardness measurement shows an increase in nanohardness of irradiated targets as compared to un-irradiated ones with the increase of fluence under both ambient conditions. (C) 2018 Elsevier Ltd. All rights reserved.

In order to generate high-spectral-irradiance white light continuum (WLC) a hollow fiber with 250 μm inner diameter was used. The hollow fiber was mounted on a V-groove holder inside a chamber filled with Argon gas. The output beam of a Ti:sapphire laser producing 30 fs pulses was focused at the entrance of the hollow fiber using a plano-convex lens. The high intensity of the incident laser beam inside the hollow fiber causes self-phase modulation leading to broadening the spectral of the input light. The broadening strength depends on many parameters such as the energy of the incident pulses, duration of incident pulses, length of hollow fiber, gas pressure inside the hollow fiber and the ratio of the beam waist diameter to inner diameter of the hollow fiber. At optimal conditions of 175 cm length hollow fiber, 500 μJ pulse energy, 150 cm focal length lens and 0,6 bar gas pressure the white light exiting the fiber possesses a spectrum ranging from 600 nm950 nm which results in generation of sub-8 fs pulses via compressing by a compressor consisting of 8 chirp mirrors.

Synthetic polymer biomaterials incorporating cells are a promising technique for treatment of orthopedic injuries. To enhance the integration of biomaterials into the human body, additional functionalization of the scaffold surface should be carried out that would assist one in mimicking the natural cellular environment. In this study, we examined poly-ε-caprolactone (PCL) fiber matrices in view of optimizing the porous properties of the constructs. Altering the porosity of a PCL scaffold is expected to improve the material’s biocompatibility, thus influencing its osteoconductivity and osteointegration. We produced 3D poly-ε-caprolactone (PCL) matrices by a fused deposition modeling method for bone and cartilage tissue engineering and performed femtosecond (fs) laser modification experiments to improve the surface properties of the PCL construct. Femtosecond laser processing is one of the useful tools for creating a vast diversity of surface patterns with reproducibility and precision. The processed surface of the PCL matrix was examined to follow the effect of the laser parameters, namely the laser pulse energy and repetition rate and the number ( N ) of applied pulses. The modified zones were characterized by scanning electron microscopy (SEM), confocal microscopy, X-ray computed tomography and contact angle measurements. The results obtained demonstrated changes in the morphology of the processed surface. A decrease in the water contact angle was also seen after fs laser processing of fiber meshes. Our work demonstrated that a precise control of material surface properties could be achieved by applying a different number of laser pulses at various laser fluence values. We concluded that the structural features of the matrix remain unaffected and can be successfully modified through laser postmodification. The cells tests indicated that the micro-modifications created induced MG63 and MC3T3 osteoblast cellular orientation. The analysis of the MG63 and MC3T3 osteoblast attachment suggested regulation of cells volume migration.

We have succeeded in realizing a method to control the spatial distribution of optical retardation as a result of nanogratings in bulk-fused silica induced by ultrashort laser pulses. A colorimetry-based retardation measurement (CBRM) based on the Michel-Levy interference color chart using a polarization microscope is used to determine the profiles of the optical retardation. Effects of the spatial overlap of written regions as well as the energy and polarization of the writing pulses on the induced retardations are studied. It has been found that the spatial overlap of lines written by pulse trains with different energies and polarizations can result in an adjustment of the induced birefringence in the overlap region. This approach offers the possibility of designing polarization-sensitive components with a desired birefringence profile.

This study reports on the evaluation of laser processed natural polymer-chitosan, which is under consideration as a biointerface used for temporary applications as skin and cartilage substitutes. It is employed for tissue engineering purposes, since it possesses a significant degree of biocompatibility and biodegradability. Chitosan-based thin films were processed by femtosecond laser radiation to enhance the surface properties of the material. Various geometry patterns were produced on polymer surfaces and employed to examine cellular adhesion and orientation. The topography of the modified zones was observed using scanning electron microscopy and confocal microscopy. Test of the material cytotoxicity was performed by evaluating the life/dead cell correlation. The obtained results showed that texturing with femtosecond laser pulses is appropriate method to initiate a predefined cellular response. Formation of surface modifications in the form of foams with an expansion of the material was created under laser irradiation with a number of applied laser pulses from N = 1–5. It is shown that irradiation with N > 5 results in disturbance of microfoam. Material characterization reveals a decrease in water contact angle values after laser irradiation of chitosan films. Consequently, changes in surface roughness of chitosan thin-film surface result in its functionalization. Cultivation of MC3T3 and ATMSC cells show cell orientational migration concerning different surface patterning. The influence of various pulse durations (varying from τ = 30–500 fs) over biofilms surface was examined regarding the evolution of surface morphology. The goal of this study was to define the optimal laser conditions (laser energy, number of applied pulses, and pulse duration) to alter surface wettability properties and porosity to improve material performance. The acquired set of results indicate the way to tune the surface properties to optimize cell–interface interaction.

Fibrous 3D matrices were fabricated from poly-epsilon-caprolactone (PCL) by fused deposition modeling. Femtosecond laser irradiation was then used to demonstrate the possibility to affect the porosity of the 3D PCL fiber meshes. The surface characteristics were analyzed by scanning electron microscopy (SEM) and confocal microscopy. The interrelationship was examined between the laser processing parameters (number of pulses, pulse energy applied) and the response of the biomaterial. The formation was demonstrated of well-defined micropores, while the original fiber structure was retained. The study of cells cultivation on the laser-modified scaffolds showed good adhesion compared to a non-modified scaffold. The results obtained showed that femtosecond laser processing can be used as an alternative non-contact tool in enhancing the porosity of artificial constructs, thus influencing the cell adhesion into fibrous meshes.

Two-photon induced polymerization (2PP) based 3D printing is a powerful microfabrication tool. Specialized two-photon initiators (2PIs) are critical components of the employed photosensitive polymerizable formulations. This work investigates the cooperative enhancement of two-photon absorption cross sections (σ2PA) in a series of 1,3,5-triazine-derivatives bearing 1-3 aminostyryl-donor arms, creating dipolar, quadrupolar and octupolar push-pull systems. The multipolar 2PIs were successfully prepared and characterized, σ2PA were determined using z-scan at 800 nm as well as spectrally resolved two-photon excited fluorescence measurements, and the results were compared to high-level ab initio computations. Modern tunable femtosecond lasers allow 2PP-processing at optimum wavelengths tailored to the absorption behavior of the 2PI. 2PP structuring tests revealed that while performance at 800 nm is similar, at their respective σ2PA-maxima the octupolar triazine-derivative outperforms a well-established ketone-based quadrupolar reference 2PI, with significantly lower fabrication threshold at exceedingly high writing speeds up to 200 mm/s and a broader window for ideal processing parameters.

The formation of nanoscale structures, variation in structural and mechanical properties of zirconium has been investigated. For this purpose Ti: sapphire laser (800nm, 30fs, 1kHz) was employed for varying number of laser pulses ranging from 500 to 2000, at a fluence of 3.6J/cm2 in ambient environments of air and ethanol. The surface morphology of irradiated zirconium samples was investigated by using Scanning Electron Microscope (SEM). SEM analysis shows the formation of various features including nanoscale Laser Induced Periodic Surface Structures (LIPSS), conical structures, droplets, pores and cavities. Relatively fine LIPSS with significantly less periodicity are formed in liquid environment because of the confinement effects of liquid. EDS analysis exhibits variation in chemical composition along with enhanced diffusion of oxygen under both ambient conditions. The crystal structure and phase analysis of the exposed targets were explored by X-ray Diffraction (XRD) and Raman spectroscopy techniques, respectively. XRD analysis confirms presence of various phases of oxides of zirconium after ablation in both air and ethanol. Raman analysis supports the EDS and XRD results. It also reveals the presence of oxides after irradiation in both air and ethanol environments. Convective motion of bubbles and pressure gradient because of confinement effects of liquid accompanied with creation of oxides is attributable for the development of nanoscale structures. Nanohardness measurement shows an increase in nanohardness with increase in number of laser pulses after irradiation in air ambient whereas, in case of ethanol decrease in nanohardness is observed.

The surface, structural, and mechanical properties of zirconium after irradiation with Ti: sapphire laser（800 nm, 30 fs,1 k Hz） have been investigated. The zirconium targets were exposed for a varying number of laser pulses ranging from 500 to 2000 at a fixed fluence of 3.6 J/cm~2 corresponding to an intensity of 1.2×10 14 W/cm~2 in ambient environments of deionized water and propanol. A scanning electron microscope（SEM） was employed to investigate the surface morphology of the irradiated zirconium. The SEM analysis shows the formation of various kinds of features including nanoscale laser induced periodic surface structures（LIPSS）, sponge like surface structure, flakes, conical structures, droplets, pores, and cavities. The energy dispersive x-ray spectroscopy（EDS） analysis exhibits the variation in chemical composition along with an enhanced diffusion of oxygen under both ambient conditions. The crystal structure and phase analyses of the exposed targets were explored by x-ray diffraction（XRD） and Raman spectroscopy techniques, respectively. The XRD analysis confirms the presence of various phases of zirconium hydride and zirconia after ablation in both de-ionized water and propanol. However, excessive hydrides are formed in the case of propanol. The Raman analysis supports the EDS and XRD results. It also reveals the presence of oxides（zirconia） after irradiation in both de-ionized water and propanol environments.The chemical reactivity of zirconium was significantly improved in the presence of liquids which were accountable for the growth of novel phases and modification in the chemical composition of the irradiated Zr. A nanohardness tester was employed to measure the nanohardness of the laser treated targets. The initial increase and then decrease in nanohardness was observed with an increase in the number of laser pulses in the de-ionized water environment. In the case of propanol,a continuous decrease in hardness was observed.