Visible Laser Radiation Research Articles

A study of the possibility of conducting selective laser processing of thin composite electrochromic Ni(OH)2-PVA films

The surfaces of thin composite electrochromic Ni(OH)2-polyvinyl alcohol films, deposited by the cathodic template method on FTO glass substrates, were proposed to be processed using laser radiation. The processing of these films was carried out in a colored state with a laser beam of a semiconductor emitter with a wavelength of 650 nm (red) with a pulse duration of 3,000 μs, the beam diameter was about 40 μm. The energy at a single point was 37.5 J/cm2. The result was a film with microholes of about 80 μm. The transparent areas of the surface did not exhibit electrochromic properties, which indicated the absence of the original electrochromic coating. The study of the properties of the laser-processed film following a certain pattern showed that the characteristics of composite Ni(OH)2-polyvinyl alcohol coatings had changed significantly. On the one hand, the coloration depth of the films decreased by several percent, on the other hand, the specific electrochemical characteristics increased significantly. The study also showed that laser processing did not lead to significant changes in the main properties of the transparent electrically conductive layer – color and resistance. Before and after laser processing, the surface resistance of FTO glasses was 12.1±0.9 and 14.4±1.2 Ohm/sq., respectively. In addition, it was found that the processing of Ni(OH)2-polyvinyl alcohol films improved the adhesion of the latter to the surface of FTO glass. Based on the data obtained, a selective method was proposed for modifying thin colored films deposited on transparent conductive oxides (FTO, ITO, AZO) by visible laser radiation. This approach to changing the properties of films can be useful for areas related to the development of sensors, microelectronics, solar cells, small-sized current sources, electrodes with high efficiency, etc.

Microfabrication and Surface Functionalization of Soda Lime Glass through Direct Laser Interference Patterning.

All-purpose glasses are common in many established and emerging industries, such as microelectronics, photovoltaics, optical components, and biomedical devices due to their outstanding combination of mechanical, optical, thermal, and chemical properties. Surface functionalization through nano/micropatterning can further enhance glasses’ surface properties, expanding their applicability into new fields. Although laser structuring methods have been successfully employed on many absorbing materials, the processability of transparent materials with visible laser radiation has not been intensively studied, especially for producing structures smaller than 10 µm. Here, interference-based optical setups are used to directly pattern soda lime substrates through non-lineal absorption with ps-pulsed laser radiation in the visible spectrum. Line- and dot-like patterns are fabricated with spatial periods between 2.3 and 9.0 µm and aspect ratios up to 0.29. Furthermore, laser-induced periodic surface structures (LIPSS) with a feature size of approximately 300 nm are visible within these microstructures. The textured surfaces show significantly modified properties. Namely, the treated surfaces have an increased hydrophilic behavior, even reaching a super-hydrophilic state for some cases. In addition, the micropatterns act as relief diffraction gratings, which split incident light into diffraction modes. The process parameters were optimized to produce high-quality textures with super-hydrophilic properties and diffraction efficiencies above 30%.

Synthesis and deposition of Silver nanostructures on the silica microsphere by laser-assisted photochemical method for SERS applications

The homogeneous distribution of nano-metallic structures on the surface-enhanced Raman (SERS) substrates plays an important factor for high-sensitive Raman scattering measurement. In this paper, we present a low-cost laser-assisted photochemical method for making a SERS probe based on silver nanostructures, which are one-timely synthesized nano-silver structures, homogeneously deposited on silica microsphere surfaces. Achieved SERS-activity substrates with a homogeneous distribution of Ag-nanostructures are verified by a mapping technique on the surface of Ag-coated microsphere for the detection of low concentration of Rhodamine 6G in aqueous solutions in a range of 10-4-10-9M. The obtained results show that a SERS microsphere probe has a good repetition of SERS-activity in any space of sensing area, and large potential for application in a biochemical sensing technique. Full Text: PDF ReferencesY. Chen et al., "Interfacial reactions in lithium batteries", J. Phys. D: Appl. Phys. 50, 02510 (2017). CrossRef T.B. Pham, H. Bui, H.T. Le, V.H. Pham, "Characteristics of the Fiber Laser Sensor System Based on Etched-Bragg Grating Sensing Probe for Determination of the Low Nitrate Concentration in Water", Sensors 17, 0007 (2017). CrossRef X. Wang, O.S. Wolfbeis, "Fiber-Optic Chemical Sensors and Biosensors (2013–2015)", Anal. Chem. 88, 203 (2016). CrossRef R. Wang, K. Kim, N. Choi, X. Wang, J. Lee, J.H. Joen, G. Rhie, J. Choo, "Highly sensitive detection of high-risk bacterial pathogens using SERS-based lateral flow assay strips", Sens. Actuators B-Chem. 270, 72 (2018). CrossRef H. Zhang et al., "Determination of Pesticides by Surface-Enhanced Raman Spectroscopy on Gold-Nanoparticle-Modified Polymethacrylate", Anal. Let. 49, 2268 (2016). CrossRef L. Chen, H. Yan, X. Xue, D. Jiang, Y. Cai, D. Liang, Y.M. Jung, X.X. Han, B. Zhao, "Surface-Enhanced Raman Scattering (SERS) Active Gold Nanoparticles Decorated on a Porous Polymer Filter", Appl. Spectrosc. 71, 1543 (2017). CrossRef A. Matikainen, T. Nuutinen, P. Vahimaa, S. Honkanen, "A solution to the fabrication and tarnishing problems of surface-enhanced Raman spectroscopy (SERS) fiber probes", Sci. Rep. 5, 8320 (2015). CrossRef J. Zhang, S. Chen, T. Gong, X. Zhang, Y. Zhu, "Tapered Fiber Probe Modified by Ag Nanoparticles for SERS Detection", Plasm. 11, 743 (2016). CrossRef W. Xu et al., "A Dual-Butterfly Structure Gyroscope", Sensors 17, 467 (2017). CrossRef K. Setoura, S. Ito, M. Yamada, H. Yamauchi, H. Miyasaka, "Fabrication of silver nanoparticles from silver salt aqueous solution at water-glass interface by visible CW laser irradiation without reducing reagents", J. Photochem. Photobio. A: Chem. 344, 168 (2017). CrossRef K. Liu, Y. Bai, L. Zhang, Z. Yang, Q. Fan, H. Zheng, Y. Yin, C. Gao, "Porous Au–Ag Nanospheres with High-Density and Highly Accessible Hotspots for SERS Analysis", Nano Lett. 16, 3675 (2016). CrossRef Z. Huang, X. Lei, Y. Liu, Z. Wang, X. Wang, Z. Wang, Q. Mao, G. Meng, "Tapered Optical Fiber Probe Assembled with Plasmonic Nanostructures for Surface-Enhanced Raman Scattering Application", ACS Appl. Mater. Interfaces 7, 17247 (2015). CrossRef

Study of Local Fields of Dendrite Nanostructures in Hot Spots Formed on SERS-Active Substrates Produced via Template-Assisted Synthesis

A procedure is proposed for template-assisted synthesis on track membranes using iodide electrolyte to produce substrates with dendritic nanostructures formed on the tips of silver nanowires. The distribution of the electromagnetic field near a silver nanorhombus irradiated with visible laser radiation is modeled because the dendrite branches are rhombus-shaped nanoparticles. Calculations indicate considerable enhancement of the local electric fields near the sharp tops of the nanorhombus.

Absorption of Powerful Light by Free Electrons in Crystals: Intraband Electron–Phonon Rabi Oscillations

The absorption of high-power visible or near-IR laser radiation by free electrons is calculated using the modified resonance approximation. The probabilities Wexc of intraband transitions at which the electron energy changes by ℏ(ω ± ωl), where ω is the frequency of light and ωl is the frequency of longitudinal optical phonons involved in the process, are determined. It is shown that specific electron–phonon Rabi oscillations at a frequency of ΩR may take place, and that the light is absorbed only up to the moment of time at which the first maximum τ1 on the dependence Wexc(t) is reached, where t is the time elapsed from the beginning of the laser pulse. It is shown that, in the case of prebreakdown light intensities, processes of high orders in the field of the light wave affect substantially Wexc, τ1, and ΩR.

Synthesis of TiO2 nanoparticles decorated with gold nanoclusters using pulsed laser ablation in liquid

Amorphous spherical titanium dioxide (TiO2) nanoparticles, decorated gold nanoparticles, are shown to be formed under irradiation of commercial TiO2 nanopowders dispersed in aqueous solution of hydrogen tetrachloroaurate (HAuCl4) by second-harmonic nanosecond pulses of an Nd : YAG laser. It is found that these hybrid nanostructures are formed during laser-induced remelting of the initial nanoparticles, stimulated by gold nanoclusters (providing more efficient absorption of visible laser radiation by titanium dioxide) recovered on their surface. The morphology and chemical composition of the newly formed hybrid nanomaterials are investigated in detail by electron microscopy, Raman spectroscopy, and energy-dispersive analysis. It is shown that the average size and number of gold nanoparticles recovered on the TiO2 surface can be controlled by varying the concentration ratio of the initial nanomaterial and HAuCl4. A spectroscopic analysis of light scattering by single hybrid nanoparticles and the results of numerical calculation of the structure of electromagnetic fields near their surface indicate good prospects of these hybrid nanomaterials for various applications in modern optics, optoelectronics, and nanophotonics; for example, for designing chemo- and biosensor platforms and new-generation solar cells.

Heat Transfer in a Water Drop Containing a Dye and Nanoparticles under Double Laser Irradiation

Heat transfer in a water drop containing eosine and ablation silver nanoparticles induced by stationary visible laser irradiation, λ = 532 nm, and pulsed IR laser irradiation, λ = 10.6 μm (VIS–IR double laser irradiation), has been studied in the temperature interval of 0.2–50°C. It has been found that the vibratory system of triplet states in a dye molecule heats up after VIS–IR laser irradiation, causing thermoluminescence. The thermoluminescence decay kinetics indicates a new distribution of electron vibration modes in the fluorescence spectrum of dye molecules. If the drop with nanoparticles is small (d < 1 mm), pulsed IR irradiation (τ = 50 ms) gives rise to a thermal front causing thermoluminescence, which travels in the drop with a velocity of 0.85 cm/s. Heat transfer in the drop during the formation of a thermal wave has been simulated.

New fabrication method for producing reduced graphene oxide flexible electrodes by using a low-power visible laser diode engraving system

The fabrication of bendable electronic devices is a scientific-technological area of very rapid advance in which new materials and fabrication techniques are being continuously developed. In these kinds of devices, the fabrication of flexible conductive electrodes adherent to the substrate is a key factor. Further, eco-friendliness, low cost and fast production are essential requirements for the successful progress of new technologies. In this work, a novel method for obtaining graphene-based flexible electrodes is presented. Conductive films were obtained by means of the visible laser irradiation of graphene oxide layers deposited on polyethylene terephthalate substrates and self-standing membranes sandwiched between glass slides. Despite the low power of the laser system, the numerical simulations indicate the development of temperatures over 1000 K throughout the irradiated material. The laser-induced spatially confined heating leads to the reduction of the graphene oxide material, whereas the glass-based sandwich assembly avoids reoxidation from the surrounding air. By scanning and pixelated modes, reduced graphene oxide electrodes, up to 100 μm in thickness, and with a resistivity as low as 6 × 10−4 Ωm, were obtained in an easy and versatile way. Proof-of-concept microsupercapacitors and electrochemical sensors were fabricated with this technique, showing promising performance.

Поглощение мощного света свободными электронами в кристаллах: внутризонные электрон-фононные осцилляции Раби

Absorption of high-intensity visible or near-IR pulsed laser radiation at free electrons in crystals is calculated in the modified resonance approximation. The probabilities $W_{exc}$ of intraband transitions with a change in the electron energy by $\hbar(\omega\pm\omega_l)$, where $\omega$ is the radiation frequency and $/omega_l$ the frequency of longitudinal optical phonons involved in the process, are derived. It is shown that specific electron–phonon Rabi oscillations with the frequency $\Omega_R$ can occur and radiation is absorbed only until the point in time $\tau_1$, at which the first maximum in the dependence $W_{exc} (t)$, where t is the time elapsed from the beginning of the laser pulse, is reached. It is shown that, in the case of prebreakdown radiation intensities, the processes of high orders in field of the radiation wave substantially influence $W_{exc}$, $\tau_1$, and $\Omega_R$.

Skin and subcutaneous fat morphology alterations under the LED or laser treatment in rats in vivo.

The main objective of this work is to quantify the impact of photodynamic/photothermal treatment by using visible LED and NIR laser irradiation through the skin of subcutaneous fat in vivo followed up by tissue sampling and histology. The optical method may provide reduction of regional or site-specific accumulations of abdominal or subcutaneous adipose tissue precisely and least-invasively by inducing cell apoptosis and controlled necrosis of fat tissue. As photodynamic/photothermal adipose tissue sensitizers Brilliant Green (BG) or Indocyanine Green (ICG) dyes were injected subcutaneously in rats. The CW LED device (625 nm) or CW diode laser (808 nm) were used as light sources, respectively. Biopsies of skin together with subcutaneous tissues were taken for histology. The combined action BG-staining and LED-irradiation (BG + LED) or ICG-staining and NIR-laser irradiation (ICG + NIR) causes pronounced signs of damage of adipose tissue characterized by a strong stretching, thinning, folding and undulating of cell membranes and appearance of necrotic areas. As a posttreatment after 14 days only connective tissue was observed at the site of necrotic areas. The data obtained are important for safe light treatment of site-specific fat accumulations, including cellulite. This work provides a basis for the development of fat lipolysis technologies and to move them to clinical applications. Schematics of animal experiment.

Scientific-Methodical Approaches to Measurements of Characteristics of Physical and Chemical Processes in Condensed Media Exposed to Laser Radiation and Their Experimental Realization

Scientific-methodical approaches to a study of nonlinear physicochemical processes are considered and an experimental setup intended for investigation of nonlinear physical and chemical processes accompanying irradiation of solids of various classes (including energetic materials) by UV, visible, and IR laser radiation is described. The possibility of synchronous multi-parameter measurements of the amplitude, spectral, kinetic, and spatial characteristics of the near-surface and bulk luminous laser plasma, solid-phase luminescence, acoustic pulses formed in the bulk of the samples, and morphology of residual damages has been demonstrated with a nanosecond time resolution. The energy density on the irradiated target surfaces varied from fractions of mJ/cm2 to 104 J/cm2 depending on the problem to be solved. The spectral range recorded for one irradiation pulse was 200–1100 nm, the spectral resolution was ~1.5 nm, and the spatial resolution was ~10 μm. A pressure pulse formed in the sample volume was recorded by an acoustic sensor with sensitivity of 0.15 V/bar and temporal resolution of ~5 ns.

Regarding the Nature of Charge Carriers Formed by UV or Visible Light Excitation of Carbon-Modified Titanium Dioxide

Although titanium dioxide gathers many of the required properties for its application in photocatalytic processes, its lack of activity in the visible range is a major hurdle yet to be overcome. Among different strategies, the post-synthesis modification of TiO2 powders with organic compounds has already led to commercially available materials, such as KRONOClean 7000. In this work, we apply diffuse reflectance transient absorption spectroscopy on this visible-light active photocatalyst and study the dynamics of the charge carriers alternatively induced by UV or visible light laser irradiation, under inert or reactive atmospheres. Our results can be interpreted by considering the material as TiO2 sensitized by an organic-based layer, in agreement with previous studies on it, and show that the oxidative power of the material is considerably diminished under visible light irradiation. By complementarily performing continuous visible light irradiation photocatalysis experiments in aerated aqueous suspensions, we show that, although the oxidation of methanol proceeds at a very slow rate, the oxidation of chlorpromazine occurs much faster thanks to its better suited redox potential.

Photoelectrochemical Reaction in an Electric Cell with a Porous Carbon Anode

A photoelectrochemical cell utilizing porous carbon derived from Binchotan charcoal as the anode is demonstrated. Visible pulse laser irradiation of the Binchotan charcoal anode induces the ablation of carbon cations into NaNO3 aqueous solution. Electrons remaining in the anode reduce the potential of the anode with respect to a platinum cathode. As the electrodes are short-circuited, photogenerated electrons are transported from the anode to the cathode as a diffusion current. The photoinduced charge density at the anode exhibits superlinear and linear excitation laser power density dependences at low and high laser power densities, respectively. This difference in excitation power dependence is caused by the valences of the carbon cations generated by absorbing two-photon energy. The revealed reaction mechanism for electron generation at the Binchotan charcoal anode in the photoelectrochemical cell suggests that the sacrificial reagent for the anode can be not only Binchotan charcoal but also any materi...

Symmetric nanostructuring and plasmonic excitation of gold nanostructures by femtosecond Laguerre – Gaussian laser beams

Femtosecond low-energy Laguerre – Gaussian pulses of tightly focused visible laser radiation were employed for single-pulse ablative nanostructuring of a 50-nm thick gold film. Similar pulses of lower energy were employed for the efficient plasmonic photoluminescence excitation of a rhodamine 6G dye monolayer in the fabricated nanostructures. The consistency between the shape and polarisation symmetries of the low-energy laser beam, on the one hand, and the gold nanostructures produced by the same beam at a high radiation energy, on the other hand, opens the way to consistent nanostructuring and surface-enhanced analytical spectroscopy with the use of nanostructures.

SERS, XPS and DFT Study of Xanthine Adsorbed on Citrate-Stabilized Gold Nanoparticles.

We have studied the adsorption of xanthine, a nucleobase present in human tissue and fluids that is involved in important metabolic processes, on citrate-reduced gold colloidal nanoparticles by means of surface-enhanced Raman scattering (SERS), absorption, and X-ray photoelectron spectroscopy (XPS) measurements, along with density functional theory (DFT) calculations. The citrate anions stabilize the colloidal suspensions by strongly binding the gold nanoparticles. However, these anions do not impair the adsorption of xanthine on positively-charged active sites present on the metal surface. We have obtained the Fourier transform (FT)-SERS spectra of adsorbed xanthine by laser excitation in the near infrared spectral region, where interference due to fluorescence emission does not usually occur. In fact, the addition of chloride ions to the Au/xanthine colloid induces the aggregation of the gold nanoparticles, whose plasmonic band is shifted to the near infrared region where there is the exciting laser line of the FT–Raman instrument. Hence, this analytical approach is potentially suitable for spectroscopic determination of xanthine directly in body fluids, avoiding fluorescence phenomena induced by visible laser irradiation.

Application of Plasmon-Induced Lithography for Creation of a Residual-Free Pattern and Simple Surface Modifications.

Here, we propose a plasmon-induced redistribution of a thin polymer layer as a unique way for a residual layer-free lithographic approach. In particular, we demonstrate an ultrafast area-selective fabrication method using a low-intensity visible laser irradiation to direct the polymer mass flow, under the plasmon-active substrates. Plasmon-supported substrates were created by thermal annealing of Ag thin films and covered by thin polystyrene layers. Then, laser beam writing (LBW) was applied to introduce a surface tension gradient through the local plasmon heating. As a result, polystyrene was completely removed from the irradiated place, without any residual layer. The proposed approach does not require any additional development steps, such as solvent or plasma treatment. To demonstrate the advantages of the proposed technique, we implemented the LBW-patterned structures for further spatially selective surface functionalization, including the metal deposition, spontaneous thiol grafting, and electrochemical deposition of ordered polypyrrole array.

Photoprintable nanowire–polymer blends synthesized by dynamic emulsion polycondensation

ABSTRACTIn this article, we report a photoprintable nanocomposite synthesized at room temperature in less than 10 s by aggressive mixing of two monomer solutions. Polycondensation occurs in the dispersed phase of the dynamic emulsion, microdroplets, in which the nanofillers are suspended. Hence, the synthesized composite microparticles have a high dispersion and high loading of nanofillers. Specifically, silver nanowire (AgNW)–nylon 66 blends with various Ag weight fractions are synthesized and studied. The poly(vinyl pyrrolidone) (PVP)‐functionalized AgNWs (by polyol synthesis) are singly dispersed and tethered to the nylon matrix by PVP with a slight depression of the glass‐transition temperature. The Ag–nylon powder melts under low‐intensity visible continuous wave laser radiation; this allows convenient photoprinting of the nanocomposite structures. Photoprinting is demonstrated at a radiation intensity of 0.3 kW/cm2 (405 nm laser) and a scan rate of 5 mm/s for a 1.49 wt % Ag content. This enhanced photothermal characteristic of the nanocomposite, which allows printing at low radiation intensities, is attributed to the efficient coupling of light to the AgNW plasmon modes and the high dispersion of nanowires in the polymer. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47670.

Laboratory Photochemistry of Covalently Bonded Fluorene Clusters: Observation of an Interesting PAH Bowl-forming Mechanism

Abstract The fullerene C60, one of the largest molecules identified in the interstellar medium (ISM), has been proposed to form top-down through the photochemical processing of large (more than 60 C atoms) polycyclic aromatic hydrocarbon (PAH) molecules. In this article, we focus on the opposite process, investigating the possibility that fullerenes form from small PAHs, in which bowl-forming plays a central role. We combine laboratory experiments and quantum chemical calculations to study the formation of larger PAHs from charged fluorene clusters. The experiments show that with visible laser irradiation, the fluorene dimer cation—[C13H9−C13H9]+—and the fluorene trimer cation—[C13H9−C13H8−C13H9]+—undergo photodehydrogenation and photoisomerization, resulting in bowl-structured aromatic cluster ions, C26H12 + and C39H20 +, respectively. To study the details of this chemical process, we employ quantum chemistry that allows us to determine the structures of the newly formed cluster ions, to calculate the dissociation energies for hydrogen loss, and to derive the underlying reaction pathways. These results demonstrate that smaller PAH clusters (with less than 60 C atoms) can convert to larger bowled geometries that might act as building blocks for fullerenes, because the bowl-forming mechanism greatly facilitates the conversion from dehydrogenated PAHs to cages. Moreover, the bowl-forming induces a permanent dipole moment that—in principle—allows one to search for such species using radio astronomy.

Laser Induced Plasmonic Heating with Au Decorated TiO2 Nanoparticles

In this study, we explore the feasibility of laser as source of photons for plasmonic heating of metal nanoparticles. Au decorated TiO2 nanoparticles with different Au wt.% loading were prepared using deposition-precipitation method and their physical and optical properties were characterized by X-Ray diffraction (XRD), Diffuse reflectance spectra (DRS) and Raman spectroscopy. The enhancement of the optical properties of Au plasmonic nanoparticles arises from localized surface plasmon resonance (LSPR) effect achieved under 532 nm laser irradiation. Additionally, the photothermal performance of Au/TiO2 nanofluid was tested compared with other nanofluids under visible laser irradiation. The results revealed that the temperature of Au/TiO2 nanofluid was significantly higher compared to that of bare TiO2 and pure milli-Q water, attributing to the plasmonic excitation of Au nanoparticles under laser irradiation.

Real-time investigations of structural and optical changes in photochromic Ag/TiO2 nanocomposite thin films under laser irradiation

Photochromic reaction dynamics in silver nanoparticles embedded in mesoporous titanium dioxide thin films is investigated by combining real-time grazing incidence small-angle x-ray scattering (GISAXS) and optical transmission measurements during UV–visible laser exposure cycles. While GISAXS probes changes in the particle size distribution, transmittance measurements are sensitive to spectral changes induced by photo-activated processes. Our results reveal a repeatable photochromic behavior with a good correlation in terms of kinetics between the morphological and optical fluctuations. Visible laser irradiation at 532 nm induces a preferential photo-dissolution of small silver particles, which in turn causes an increase in transmittance near the excitation wavelength. Furthermore, the photo-dissolution process can be significantly accelerated and amplified by associating visible laser with x-ray irradiation. Under UV laser irradiation at 360 nm, the bleaching process can be reverted by photocatalytic reduction with the mesopores in the TiO2 film acting as molds, which have the ability to confine the nanoparticle growth. However, in the irradiation conditions used in the present study, it appears that the photocatalytic growth of silver nanoparticles is slower than the photo-dissolution process, whereas its efficiency gradually degrades throughout the exposures to UV light.