Laser Fluence Research Articles

Colloidal Titanium Nitride Nanoparticles by Laser Ablation in Solvents for Plasmonic Applications.

Titanium nitride (TiN) is a candidate material for several plasmonic applications, and pulsed laser ablation in liquids (PLAL) represents a rapid, scalable, and environmentally friendly approach for the large-scale production of nanomaterials with customized properties. In this work, the nanosecond PLAL process is developed, and we provide a concise understanding of the process parameters, such as the solvent and the laser fluence and pulse wavelength, to the size and structure of the produced TiN nanoparticles (NPs). TiN films of a 0.6 μm thickness developed by direct-current (DC) magnetron sputtering were used as the ablation targets. All laser process parameters lead to the fabrication of spherical NPs, while the laser pulse fluence was used to control the NPs' size. High laser pulse fluence values result in larger TiN NPs (diameter around 42 nm for 5 mJ and 25 nm for 1 mJ), as measured from scanning electron microscopy (SEM). On the other hand, the wavelength of the laser pulse does not affect the mean size of the TiN NPs (24, 26, and 25 nm for 355, 532, and 1064 nm wavelengths, respectively). However, the wavelength plays a vital role in the quality of the produced TiN NPs. Shorter wavelengths result in NPs with fewer defects, as indicated by Raman spectra and XPS analysis. The solvent type also significantly affects the size of the NPs. In aqueous solutions, strong oxidation of the NPs is evident, while organic solvents such as acetone, carbides, and oxides cover the TiN NPs.

Fiber Laser Writing of Highly Sensitive Nickel Nanoparticle-Incorporated Graphene Strain Sensors.

Unlocking new dimensions in wearable sensor technology, this research highlights ultrasensitive stretchable strain sensors fabricated with the customized laser-induced graphene (LIG) decorated with uniformly distributed nickel nanoparticles with a fiber laser writing process. The nickel nanoparticle-incorporated LIG (Ni-NPs@LIG) strain sensors fabricated by a simple all-laser-based method utilize a commercial fiber laser. The Ni-NPs@LIG sensors showcase an impressive gauge factor, reaching up to 248 for strain values below 5%, demonstrating a sensitivity increase of up to 430% compared to the pure LIG sensors. Moreover, these sensors offer adjustable strain sensitivity based on laser fluence. The key advancement of this study lies in the direct laser writing of highly porous nickel-graphene nanostructures with adjustable properties, making them applicable across a broad range of applications. As an application demonstration, the strain sensors were employed to assess the small deformation of a pouch battery or track the large deformation of a balloon surface.

Nanosecond pulsed laser irradiation of titanium in acetone: The effects of coating film structures on the hydrogen absorption properties

Pulsed laser irradiation was performed on titanium in acetone and then the hydrogen storage properties were investigated under a hydrogen atmosphere. TiOxCy films were formed by the irradiation of Ti powders with a fluence of 0.36 J cm−2. The irradiation increased the hydrogen absorption temperatures. Thus, the TiOxCy films showed a specific kind of hydrogen barrier effect. Irradiation with a fluence of 0.36 J cm−2 was performed to coat the Ti plate. Although the TiOxCy films formed on the surface, the amount of hydrogen absorption increased compared with the non-irradiated plate because of the change in surface chemical bonding states and high porosity of the films due to the irradiation. The phases generated by irradiation were controlled by the laser fluence. With a low fluence of 0.17 J cm−2, TiO2 films were formed instead of TiOxCy films, and these dense films showed better hydrogen barrier effects than the non-irradiated plate.

High-strength and impermeable sapphire/aluminum joints fabricated by ultrafast laser microwelding: Microstructures and joining mechanism

In this work, robust joints of sapphire and aluminum were successfully achieved by direct ultrafast laser transmission microwelding. Effects of laser parameters on the microstructures and mechanical properties were comprehensively studied. The welding process highly depended on the laser ablated metal nanoparticles within the heterojunction, as well as the thermal accumulation under multiple laser pulses irradiation. It showed that lack of fusion at the sapphire/aluminum interface can occur due to the incomplete melting of ablated nanoparticles at low laser fluence (<0.48 J/cm2). While serious cavities and cracks inside the brittle sapphire were formed with the intensified stress concentration after melting-solidification process at excessive laser fluence (>0.64 J/cm2). A nearly defect-free joint was obtained with max. shear strength of 128.1 ± 8.2 MPa at room temperature, when the laser fluence was 0.56 J/cm2. The high shear strength can be attributed to the tortuous interface with wide elemental transition layer. Meanwhile, the welded sapphire/aluminum joints exhibited high reliability under extreme service temperatures, which the shear strength can reach 159.8 ± 8.96 MPa at −50 °C and 80.6 ± 11.1 MPa at 200 °C. The sealing tests also showed the excellent impermeability of laser welded sapphire/aluminum structure, confirming the micro-crack free joint formation. This work demonstrates the feasibility of using ultrafast laser to achieve high-quality sapphire/aluminum joint, which is promising in heat-dissipation substrate manufacturing in power semiconductor devices.

Modeling and simulation of laser-ignited Al-PTFE reactive material in vacuum

Despite extensive investigations elucidating the initial response behavior of aluminized polytetrafluoroethylene (Al-PTFE) under atmospheric pressure, research on their response in lean-oxygen environments pertinent to propulsion and explosion scenarios is still lacking. This paper theoretically analyzes the multi-physical processes of laser-ignited Al-PTFE, identifying the initial response, main chemical reaction paths, and gas-phase product flow mechanisms. A dynamic reaction model of Al-PTFE considering material moving front, chemical reactions, gas-phase product dynamics, and variations in thermophysical properties, was developed. The robust coupling scheme in the model addresses nonlinear equations and fluid-solid coupling boundary conditions. Validation was achieved by comparing the ablation depth and plume number density field calculated by the model with the experimental results in the literature. The model reveals a positive correlation between laser fluence and both temperature growth rate and ablation depth of Al-PTFE, with the effects mainly observed in the full width at half maximum (FWHM) of the pulsed laser due to the thermal decomposition of the PTFE matrix. Simulations of the equilibrium constants and molar fractions of 19 components in the Al-PTFE ablation plume within the temperature range of 2000 K to 30,000 K at 0.001 Pa indicate that the equilibrium constants for dissociative reactions exceed those for ionization reactions, primarily in the early plume formation stages. Analysis of kinetic parameters and ambient pressure effects shows that during laser ablation, the maximum temperature of the plume initially appears near the ablation surface, shifting to the front, where the maximum velocity is always located. An elliptical shock wave forms due to adiabatic expansion of the plume, creating a cavity inside the plume. Lower ambient pressure increases plume expansion velocity, temperature, and size.

Influence of the Glycidyl Azide Polymer on the Energy Release of Aluminum Sub-Micron Particles under Ultrafast Heating Rates Stimulated by Electric Explosion and Solid Laser

Glycidyl azide polymer (GAP)-coated sub-micron aluminum (sub-mAl@GAP) particles exhibit higher heat release than their uncoated counterparts under low heating rates. However, their application in explosives has been hindered due to a lack of understanding of their energy release characteristics under heating rates of detonation levels. To address this problem, the energy release performances of sub-mAl@GAP particles under ultrafast heating rates stimulated by an electric explosion of wire and high-energy laser were studied. The results showed that the reaction of sub-mAl@GAP particles was more violent than that of an uncoated counterpart under an electric explosion stimulus. Additionally, the reaction time of the former was 0.4 ms shorter than that of the latter. In addition, the propagations of shock waves of the sub-mAl@GAP and sub-mAl were analyzed. The propagation distances of shock waves of the sub-mAl@GAP were all longer than those of sub-mAl under laser fluences of 0.5 J/cm2, 1.2 J/cm2, and 2.4 J/cm2. The distance difference gradually increased with the decrease in the laser fluence. Under a laser fluence of 0.5 J/cm2, the velocity and distance differences of the sub-mAl@GAP and sub-mAl were both the largest due to the energy contribution from the GAP. In conclusion, the fast decomposition rate of the GAP and its energy contribution would benefit the energy release of sub-mAl under ultrafast heating rates.

A comparative study of laser fluence effect on surface modification and hardness profile of austempered ductile iron

The impact of laser transformation hardening (LSH) and Laser surface melting (LSM) on an austempered ductile iron (ADI) alloy was investigated. Various laser fluences (J mm−2) were irradiated on the ADI specimens, obtained by different beam powers and scanning speeds to reach the optimum parameters to attain a surface with a good combination of high hardness and deep hardened depth, together with obtaining minimal distortion and crack-free surface. ADI surfaces were treated by means of high-power Nd:YAG laser in continuous wave mode. A detailed investigation of the obtained microstructure was characterized via optical and scanning electron microscopy attached to an EDX analyzer as well as X-ray diffraction analysis. Such a wide laser fluence range has a considerable effect on the achieved microstructure. A process parameter map was established which indicated that three different laser treatments were induced under such values of laser fluences: a laser transformation hardening, a partial laser melting, and a complete laser melting. The results revealed that to produce a hardened microstructure, specimens have to be operated within a very small range of laser fluence from 9.6 up to 29 J mm−2, achieving surface hardness values around 900 HV0.1 and depths of approximately 184–700 μm, respectively. Meanwhile, partial melting of the treated layer took place at a medium energy density range from 37 to 112 J mm−2, by a further increase in laser fluence (120–360 J mm−2), complete melting occurred which resulted in a deeper treated layer that reached 3.5 mm with an increase in microhardness value to almost 1100 HV0.1 at 360 J mm−2. The obtained microstructure in case of low laser fluence consisted of an austenite dendritic structure with undissolved graphite nodules, however, at medium and high laser fluence, the microstructure contains large cementite plates, iron-silicon carbides, a small area of ledeburite structure, and some retained austenite. The quantitative amounts of such phases directly depend on the applied laser fluence. Such phases were identified by means of EDX analysis.

Computational modelling of scleral photocrosslinking: from rat to minipig to human.

Selective scleral crosslinking has been proposed as a novel treatment to increase scleral stiffness to counteract biomechanical changes associated with glaucoma and high myopia. Scleral stiffening has been shown by transpupillary peripapillary scleral photocrosslinking in rats, where the photosensitizer, methylene blue (MB), was injected retrobulbarly and red light initiated crosslinking reactions with collagen. Here, we adapted a computational model previously developed to model this treatment in rat eyes to additionally model MB photocrosslinking in minipigs and humans. Increased tissue length and subsequent diffusion and light penetration limitations were found to be barriers to achieving the same extent of crosslinking as in rats. Per cent inspired O2, injected MB concentration and laser fluence were simultaneously varied to overcome these limitations and used to determine optimal combinations of treatment parameters in rats, minipigs and humans. Increasing these three treatment parameters simultaneously resulted in maximum crosslinking, except in rats, where the highest MB concentrations decreased crosslinking. Additionally, the kinetics and diffusion of photocrosslinking reaction intermediates and unproductive side products were modelled across space and time. The model provides a mechanistic understanding of MB photocrosslinking in scleral tissue and a basis for adapting and screening treatment parameters in larger animal models and, eventually, human eyes.

Modification in electrical conductivity correlated with surface, structural & optical characteristics of graphite ions implanted CR-39

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 × 108 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 × 1012 to 92 × 1015 ions/cm2, 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 × 1015 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/Ǻ, in the CR-39 targets.

Defect-Rich CuZn Nanoparticles for Model Catalysis Produced by Femtosecond Laser Ablation.

Femtosecond laser ablation of Cu0.70Zn0.30 targets in ethanol led to the formation of periodic surface nanostructures and crystalline CuZn alloy nanoparticles with defects, low-coordinated surface sites, and, controlled by the applied laser fluence, different sizes and elemental composition. The Cu/Zn ratio of the nanoparticles was determined by energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and selected area electron diffraction. The CuZn nanoparticles were about 2-3 nm in size, and Cu-rich, varying between 70 and 95%. Increasing the laser fluence from 1.6 to 3.2 J cm-2 yielded larger particles, more stacking fault defects, and repeated nanotwinning, as evident from high-resolution transmission electron microscopy, aided by (inverse) fast Fourier transform analysis. This is due to the higher plasma temperature, leading to increased random collisions/diffusion of primary nanoparticles and their incomplete ordering due to immediate solidification typical of ultrashort pulses. The femtosecond laser-synthesized often nanotwinned CuZn nanoparticles were supported on highly oriented pyrolytic graphite and applied for ethylene hydrogenation, demonstrating their promising potential as model catalysts. Nanoparticles produced at 3.2 J cm-2 exhibited lower catalytic activity than those made at 2.7 J cm-2. Presumably, agglomeration/aggregation of especially 2-3 nm sized nanoparticles, as observed by postreaction analysis, resulted in a decrease in the surface area to volume ratio and thus in the number of low-coordinated active sites.

High-density nanodot structures on silicon solar cell surfaces irradiated by ultraviolet laser pulses below the melting threshold fluence

The surface morphology of silicon solar cells irradiated with KrF excimer laser pulses (λ = 248 nm, τ = 20 ns) was investigated below the experimentally observed melting threshold fluence (F th) of 0.47 J cm−2 (±20%). At laser fluences of 0.23–0.48 J cm−2 (equivalent to 0.49F th to 1.0F th), nanodot structures with a height and width of approximately 60–120 nm were periodically formed with an interdot spacing similar to the laser wavelength. The observed nanodot density (29 dots μm2) was higher than that previously obtained at longer wavelengths. Furthermore, crystallinity analysis by micro-Raman spectroscopy revealed a Raman shift of 519.56 cm−1 after irradiation (N= 1500 pulses), compared with 518.27 cm−1 prior to irradiation. A laser fluence of 0.41 J cm−2 ( = 0.87F th) was found to induce compressive stress on the silicon solar cell surface.

Annealing of bismuth telluride-based thick films by laser irradiation

Interest towards fabrication and post-processing of thermoelectric micro-sized devices has increased in recent years. The coupling of inexpensive deposition technologies and fast laser treatments on “as-deposited” films is an attractive solution for industrial scalability. In this work, we propose an approach never reported before in literature: the utilization of a ns-pulsed active fibre laser to directly densify p-type bismuth telluride-based thick films deposited on silicon. A feasibility study was conducted on the material to determine optimal laser parameters: the treated products were characterized, and it was concluded that a value of laser fluence as low as 4.5 mJ cm−2 is sufficient for densification. The material resulted cracked after the laser treatment, and it was demonstrated by SEM and profilometric analyses that shrinking occurs and sintering necks are formed; further, the arising of second phases after annealing was excluded by means of XRD analysis. Envisioning an industrial large area process with linear diode arrays source, a prediction of the laser power requirements to irradiate 1 mm2 films in selected conditions is presented. More extensive studies will be performed to determine a narrower parameters window and determine a relationship between the film thickness and laser parameters for future applications to as-deposited films.

Investigations on MoS2 plasma by infra-red pulsed laser irradiation in high vacuum

MoS2 targets were irradiated by infra-red (IR) pulsed laser in a high vacuum to determine hot plasma parameters, atomic, molecular and ion emission, and angular and charge state distributions. In this way, pulsed laser deposition (PLD) of thin films on graphene oxide substrates was also realized. An Nd:YAG laser, operating at the 1064 nm wavelength with a 5 ns pulse duration and up to a 1 J pulse energy, in a single pulse or at a 10 Hz repetition rate, was employed. Ablation yield was measured as a function of the laser fluence. Plasma was characterized using different analysis techniques, such as time-of-flight measurements, quadrupole mass spectrometry and fast CCD visible imaging. The so-produced films were characterized by composition, thickness, roughness, wetting ability, and morphology. When compared to the MoS2 targets, they show a slight decrease of S with respect to Mo, due to higher ablation yield, low fusion temperature and high sublimation in vacuum. The pulsed IR laser deposited MoS x (with 1 < x < 2) films are uniform, with a thickness of about 130 nm, a roughness of about 50 nm and a higher wettability than the MoS2 targets. Some potential applications of the pulsed IR laser-deposited MoS x films are also presented and discussed.

Simplifying tailored generation of complex structured femtosecond pulses with easily fabricated phase plates

This article presents a novel approach to targeted 4f pulse shaping using phase plates fabricated by single-point diamond turning (SPDT) machining. The manufacturing of the phase plates using SPDT is versatile, cost-effective, fast, robust, and applicable across a wide range of optical materials, spanning from visible to far-infrared spectra (e.g., PMMA, ZnSe). Manufactured profiles can be used for phase manipulation and pulse structuring, analogously to programable spatial light modulators (SLM). We demonstrate that the pulse waveforms can be reproduced with high fidelity by simple simulations based on calculating optical path differences induced by the phase plate for each wavelength and taking into account the finite focal spot. The simulated and reconstructed frequency-resolved optical gating spectrograms featured G errors between 1–2% and intensity errors between 0.02–0.06. Even for complex structured pulses with the rms value of the time-bandwidth product reaching 12, our method maintains high precision, in some cases even reaching lower G error compared to simpler waveforms. Finally, we also show that the phase plate can be used to attain a set of uncorrelated pulse waveforms by moving the plate relatively to the dispersed laser spectrum. Overall, this approach bypasses common limitations associated with pulse shaping using SLMs, such as pixelation, pixel cross-talk, and spectral or laser fluences constraints.

Versatile femtosecond laser interference patterning applied to high-precision nanostructuring of silicon

We present a high-precision nanostructuring technique based on beam interference from a commercial Ti:Sa femtosecond amplified laser (800 nm, 120 fs, 1 kHz, 1 mJ). Its potential and versatility is illustrated by applying the technique to the nanostructuring of silicon. Employing commercial and ad-hoc laser-fabricated diffractive optical elements together with standard optical components, periodic line gratings and spot arrays with tunable periods down to 650 nm can readily be fabricated. Moreover, fabrication of millimeter-size diffraction gratings via multipulse irradiation at processing speeds up to 0.5 mm/s is demonstrated. The variety of structures written in crystalline silicon feature amorphous fringes and dots with widths down to 300 nm. The corresponding complex topography profiles consist of surface elevations and depressions with sizes down to 120 nm that can be controlled by the laser fluence and fringe width, demonstrating the presence of several competing matter reorganization processes in the molten phase. The exceptional high-contrast ratio of the fringe intensity together with a near-Gaussian intensity envelope of the laser spot enable patterning with well-defined local fluences, paving the way for single-pulse fluence-dependent studies. The high-quality experimental data that can be obtained with this technique can prove critical for modelling attempts aimed at unravelling the underlying formation mechanisms of complex surface topographies in a wide range of materials. Furthermore, the technique presented here has outstanding potential for the rapid and versatile fabrication of high-precision metasurfaces.

Time-Resolved X-ray Emission Spectroscopy and Resonant Inelastic X-ray Scattering Spectroscopy of Laser Irradiated Carbon.

The existence of liquid carbon as an intermediate phase preceding the formation of novel carbon materials has been a point of contention for several decades. Experimental observation of such a liquid state requires nonthermal melting of solid carbon materials at various laser fluences and pulse properties. Reflectivity experiments performed in the mid-1980s reached opposing conclusions regarding the metallic or insulating properties of the purported liquid state. Time-resolved X-ray absorption studies showed shortening of C-C bonds and increasing diffraction densities, thought to evidence a liquid or glassy carbon state, respectively. Nevertheless, none of these experiments provided information on the electronic structure of the proposed liquid state. Herein, we report the results of time-resolved resonant inelastic X-ray scattering (RIXS) and time-resolved X-ray emission spectroscopy (XES) studies on amorphous carbon (a-C) and ultrananocrystalline diamond (UNCD) as a function of delay time between the irradiating pulse and X-ray probe. For both a-C and UNCD, we attribute decreases in RIXS or XES signals to transition blocking, relaxation, and finally, ablation. Increased signal at 20 ps following the irradiation of the UNCD is attributed to the probable formation of nanoscale structures in the ablation plume. Differences in the amount of signal observed between a-C and UNCD are explained by the difference in sample thickness and, specifically, incomplete melting of the UNCD film. Comparisons to spectral simulations based on MD trajectories at extreme conditions indicate that the carbon state in our experiments is crystalline. Normal mode analysis confirmed that symmetrical bending or stretching of the C-C bonds in the diamond lattice results in XES spectra with small intensity differences. Overall, we observed no evidence of melting to a liquid state, as determined by the lack of changes in the spectral properties for up to 100 ps delays following the melting pulses.

Enhancing photodetection performance through laser fluence control: SnO2 nanostructured deposited on porous silicon

In this study, we have covered a porous silicon (PS) layer with tin dioxide (SnO2) nanostructured via a pulsed laser deposition process to produce a broadband photoresponse device. The impact of laser fluence on the optical, electrical, and structural characteristics of the fabricated photodetector was identified. The optical features analysis indicated that the SnO2 films covered on porous silicon have a direct energy gap varying from 3.62 to 3.67 eV as a function of laser fluence. The X-ray diffraction investigation proved that the SnO2 nanostructure has a tetragonal rutile nature. The Field-emission scanning electron microscopy emphasised that produced SnO2 nanostructures have a mean size of 81.76–98.68 nm, and nanoparticle agglomeration was remarked. The photoluminescence emissions of SnO2 nanostructure placed on porous silicon displayed a variety of overlapping intensities in the near-ultraviolet/visible spectrum between 369 and 506 nm, while the intense red band decreased in intensity and shifted towards longer wavelengths. Fourier-transformed infrared spectroscopy investigation indicates the existence of the Sn-O-Si bond in the formed structure.The dependence of the optoelectronic characteristics of PS/n-Si and SnO2/PS/n-Si photodetector on laser fluence has been performed. Produced heterojunctions have remarkable rectification properties with ideality factors ranging from 2.27 to 2.91, relying on the laser fluence. The spectral responsivity analysis showed that SnO2/PS/n-Si photodetectors exhibit three response bands at ∼366 nm, ∼621 nm, and ∼806 nm, regarding the highest responsivity of 0.21 A/W, 0.33 A/W, and 0.43 A/W, respectively. The findings suggest that SnO2/PS/n-Si heterojunction photodetectors are suitable for developed ultraviolet–visible light detection enhanced photodiodes that are cost-effective and convenient for use in wearable and portable devices without expensive extra gadgets.

Seed-guided high-repetition-rate femtosecond laser oxidation for functional three-dimensional silicon structure fabrication

Laser oxidation provides a flexible maskless functional three-dimensional silicon structure fabrication strategy. Here, oxide layers are fabricated on silicon substrates by high-repetition-rate femtosecond laser irradiation. Formation mechanisms of the femtosecond laser oxidation are analyzed to tune the oxide layer morphology. When the laser fluence is high, the oxidation process is accompanied by laser ablation, so the oxide layer is always on top of laser ablated groove. To obtain the flat oxide layer, defect is firstly generated on silicon substrate by the laser irradiation at a high laser fluence of 126 mJ/cm2, function as a high optical absorption. It is called seed as it can assist to achieve lower fluence laser oxidation at 38 mJ/cm2 and result in a flat oxide layer. Full width at half-maximum of the oxide layer is also reduced. The laser fabricated oxide layers are used as etching masks. Three-dimensional silicon gratings are fabricated by deep reactive ion etching, which demonstrate desirable beam diffraction properties.

Impact of an Infrared Pulsed Laser on the Optical Properties of Polycarbonate/Polyethylene Oxide/Chromium Oxide Nanocomposite Films

Nanocomposite films (NC) of amorphous polycarbonate (PC), semicrystalline polyethylene oxide (PEO), and chromium oxide (Cr2O3) nanoparticles (NP) were synthesized. We believe that this study is novel in the area of the effect of laser radiation on such NC. The synthesized Cr2O3 had a nanonature of average particle size 29 nm, as indicated from the Rietveld refinement of the XRD scans. Samples of the PC-PEO/Cr2O3 NC films were irradiated with infrared energy fluences ranging from 5 to 95 Joule/cm2 (J/cm2) using an infrared pulsed laser. We used UV-vis spectroscopy and the International Commission on Illumination (CIE) color changes technique to investigate the resulting effects of the laser irradiation on the optical bandgap energy and color properties of the prepared films. As the laser fluence increased up to 95 J/cm2, the maximum fluence used, both the direct and indirect bandgaps decreased. The Urbach energy showed an opposite tendency; it increased from 0.32 to 0.56 eV. This can be attributed to the dominance of chain crosslinks that destroyed the ordered structure and thus increased the amorphous regions. Also, the optical dielectric loss (ε″) aided in detecting the nature of the microelectronic transitions. It was found that the PC/PEO/Cr2O3 NC films had direct allowed transitions. Additionally, the effect of laser irradiation on the absorbance, refractive index, real and imaginary dielectric parameters, and optical conductivity of the blend composite samples were studied. Moreover, the optical color changes between the pristine and the irradiated films were evaluated. The pristine blend film was uncolored. It showed significant color changes when irradiated with the laser at increasing fluences up to 95 J/cm2. The change in the optical properties of PC/PEO/Cr2O3 NC film suggested its usage as a promising candidate for future optoelectronics manufacturing.

Optical Effects of Focused Fractional Nanosecond 1064-nm Nd:YAG Laser: Techniques of Application on Human Skin.

Considering the pulse widths of picosecond and nanosecond lasers used in cutaneous laser surgery differ by approximately one order of magnitude, can nanosecond lasers produce the optical effect in human skin similar to laser-induced optical breakdown (LIOB) caused by picosecond lasers? Cutaneous changes induced by a focused fractional nanosecond 1064-nm Nd:YAG laser were evaluated by VISIA-CR imaging, histological examination, and harmonic generation microscopy (HGM). A focused fractional nanosecond 1064-nm Nd:YAG laser can generate epidermal vacuoles or dermal cavities similar to the phenomenon of LIOB produced by picosecond lasers. The location and extent of photodisruption can be controlled by the laser fluence and focus depth. Moreover, laser-induced shock wave propagation and thermal degeneration of papillary collagen can be observed by HGM imaging. Focused fractional nanosecond lasers can produce an optical effect on human skin similar to LIOB caused by picosecond lasers. With techniques of application, the treatment can induce epidermal and dermal repair mechanisms in a tunable fashion to improve skin texture, wrinkles, scars, and dyspigmentation, without disrupting the epidermal surface.