Laser Irradiation Time Research Articles

Self-functionalized ultrastable water suspension of luminescent carbon quantum dots

Abstract Crystalline graphite microparticles are good source for fabricating carbon based nanodots. In spite of their tremendous applications in biomedical research, the stability and non-toxicity of the product material has not been addressed. In this paper, we show that by nanosecond laser irradiation of graphitic microparticles in water, a highly stable water suspension of luminescent carbon quantum dots of high purity is generated. The sizes of the quantum dots are tuned in the range from 5 nm to 15 nm by varying the laser irradiation time. Quantum confinement is strongly evident from the optical absorption and photoluminescence spectra. Interestingly, we observed the quantum dots are self-functionalized during the fragmentation process. FTIR spectrum shows the presence of unsaturated CO bond at the surface of the quantum dots resulting in the development of similar charges. Due to the repulsive Coulombic force, these quantum dots remain stable for a very long period of time avoiding the use of any unwanted surface ligands or surfactants.

Feasibility Study of Cylindrically Diffusing 532 nm Wavelength for Treatment of Pancreatic Cancer

Laser ablation may provide a minimally invasive palliative treatment for pancreatic cancer. The aim of the current study was to assess the feasibility of a 532-nm laser equipped with a cylindrical light diffuser for the treatment of pancreatic cancer. Monolayers of BxPC-3 human pancreatic cancer cell were exposed to 532 nm laser light. Power levels of 5 - 7 W were used to uniformly target the entire cell colonies for 60 and 120 seconds. The cells were incubated for 24 hours after treatment and viabilities were determined by using a MTT assay. Laser ablation was performed by using the cylindrical light diffuser on six pancreatic tumor tissues obtained from pancreatic cancer xenograft mouse models, which were exposed to the 532 nm light at 5W or 7W for 10 to 30 seconds. In the in vitro study, the survival rates of the pancreatic cancer cells were reduced by 6.6% to 98.9% after the treatment, and the survival rates were reduced by increasing laser power and/or irradiation time. In the pancreatic tumor tissues, a homogenous circular ablation zone was observed in all tumors and the ablation distance induced by the laser irradiation showed to be constant from the diffuser to all directions (standard deviation, 0.3 - 1.3 mm). Ablation distance and area increased with increasing laser power and/or irradiation time. The 532 nm laser effectively killed pancreatic cancer cells, and the cylindrical light diffuser was found to be suitable for laser ablation as it provided uniform ablation in pancreatic cancer.

Effect of biocompatible nucleants in rapid crystallization of natural amino acids using a CW Nd:YAG laser

Laser-induced crystallization is emerging as an alternative technique to crystallize biomolecules. However, its applications are limited to specific small molecules and some simple proteins, possibly because of the need to use high-intensity, pulsed lasers and relatively long laser irradiation time. Both these factors tend to denature biological molecules. If the laser-intensity and time required to crystallize biomolecules were to be reduced, laser-induced crystallization may well become of widespread utility. We report here the crystallization of nineteen natural amino acids by a laser-induced method in combination with one of three nucleants: aluminum, coconut coir, and peacock feather barbule. We have utilized a low-power, continuous wave (CW) Nd:YAG laser (λ = 1064 nm). The advantages of our method are (i) the use of very small laser powers (60 mW), and (ii) the ability to obtain diffraction quality crystals within a mere few seconds. For most amino acids our method yields several orders of magnitude reduction in crystallization time. The use of biocompatible nucleants like coir fibres and peacock feather barbules are novel; their non-toxic nature may find broad applicability in rapid crystallization of diverse biological molecules.

Investigation on rock breaking for sandstone with high power density laser beam

High power density laser was applied during rock breaking for sandstone with different laser parameters. The fracture morphologies and quantitative characterization as well as the parameters on specific energy and rate of perforation were analyzed. It was found that a complex crack net structure was formed and the cracks area and length on the surface of sandstone specimen almost increased linearly with the number of laser perforation. Furthermore, the diameter and depth of laser perforation, the maximum width of cracks, the maximum depth and total circumferential length of side cracks increased with laser power and laser irradiation time. The experimental results demonstrated that the SE values gradually decreased with laser power while the ROP values increased. However, the SE values of sandstone by laser perforation presented a trend of first increase and then decrease, while the ROP values decreased gradually with laser irradiation time. A smooth glaze layer was formed on the inner wall of the laser perforation, where there also was plenty of shrinkage hole. Obvious cracks were generated and propagated along the inner wall. Typical brittle fracture occurred with the mix fracture mechanisms of intergranular fracture and transgranular fracture.

Tailoring of Magnetic Properties of NiO/Ni Composite Particles Fabricated by Pulsed Laser Irradiation.

We present NiO/Ni composite particles with face-centered cubic (fcc) structure prepared by a pulsed laser irradiation of NiO nanoparticles dispersed in liquid. The sizes of particles and the Ni content in NiO/Ni composites were controlled by tuning the laser parameters, such as laser fluence and irradiation time. We found that the weight fraction of Ni has a significant impact on magnetic properties of composite particles. Large exchange bias (HEB) and coercivity field (HC) were observed at 5 K due to the creation of heterojunctions at interfaces of ferromagnetic Ni and antiferromagnetic NiO. For the NiO/Ni composites with 80% of NiO we have observed the largest values of exchange bias (175 Oe) and coercive field (950 Oe), but the increase of Ni weight fraction resulted in the decrease of both HC and HEB values.

Microcrack Analysis of Dental Hard Tissue After Root Canal Irradiation with a 970-nm Diode Laser.

The aim of the present study was to investigate differences in the amount of dentin microcracking caused by the use of a 970-nm diode laser with different parameters for endodontic disinfection procedures. Forty dental roots underwent mechanical endodontic preparation in a standardized manner. Each sample was randomly allocated to 4 groups receiving constant or interval laser irradiation time, calcium hydroxide disinfection, or a control group, with 10 samples per group. Transmission microscopy of all samples was performed at T0, before preparation; T1, immediately after endodontic preparation; and T2, after laser application in the laser groups and after 1 week of storage in the control and calcium hydroxide groups. The microcracks at each measurement point were color labeled, layered, and compared. No significant differences were noted at T0 and T1 (p > 0.05). Statistically significant differences in the overall amount of microcracking were observed between the constant laser group and all other groups at T2 (p < 0.05). There were no statistically significant differences between the interval laser group, the calcium hydroxide group, and the control group at T2 in relation to the overall amount of microcracking (p > 0.05). When the root sections were analyzed separately, the coronal section did not show any statistically significant differences between the constant laser and interval laser groups (p > 0.05). The middle and apical root sections in the constant laser group showed the significantly largest amount of crack formation in comparison with the other groups (p < 0.05). The statistically significantly smallest amount of crack formation was observed in the apical third for all groups (p < 0.05). Clinically proposed laser protocol seems to be able to prevent side effects to the tissue, such as microcracks of the root canal dentine.

Ultrafast electron dynamics and orbital-dependent thermalization in photoexcited metals

We use a time-dependent density functional theory (TDDFT) to analyze nonequilibrium dynamics of laser-excited electrons in transition metals (Ni, Cr, Cu) and shed light on the ultrafast thermalization process from a microscopical point of view. As a first result, after instant increase of the electron temperature up to 50 000 K, we observe that the dynamics of electron density of states is faster than a laser subcycle, on the attosecond timescale. This is related to an ultrafast rearrangement of excited electrons in space to accommodate strong changes in ion screening. Secondly, we show that the electron thermalization dynamics strongly depends on the electronic structure of a given metal. Excited by a 7-fs laser pulse, $d$-block transition metals exhibit two subsystems of electrons, each one achieving its own temperature. Due to a higher localization, electrons from $d$ block stay cold, while excited delocalized $sp$ electrons rapidly reach a high temperature. Electrons of each band of energy are mutually thermalized within the time of the laser pulse. Much more time is however needed to reach equilibrium of the whole electronic system. These results redraw the validity limits of current two-temperature models during the laser irradiation time, potentially impacting further material reaction.

Structural changes and electrical properties of nanowelded multiwalled carbon nanotube junctions.

This study proposes an efficient approach that uses a 1064nm continuous fiber laser to achieve nanoscale welding of crossed multiwalled carbon nanotubes (MWCNTs). We investigate the effects of laser irradiation time (from 1 to 6s) on the structure changes and the welding quality of crossed MWCNTs using a scanning electron microscope, transmission electron microscope, and Raman spectroscopy. The experimental results demonstrate that (1)after 2 or 3s laser irradiation, moderate temperature of MWCNTs can be formed and can cause a higher degree of graphitization and (2)the degree of graphitization and effective contact of nanowelded MWCNT junctions strongly affects its electrical properties.

Enhancement of long wavelength preheating in dual-beam laser induced breakdown spectroscopy

Dual-beam laser induced breakdown spectroscopy (LIBS) is more sensitive than conventional single-pulse LIBS. A combined configuration of Nd:YAG and CW- CO2 lasers is used to improve the emission intensity of LIBS. The plasma of Al sample was observed under CW-CO2 laser and Nd:YAG laser excitation. The enhancement radiation was obtained from dual-beam LIBS rather than single LIBS, which indicated that IR preheating can cause significant enhancement of plasma. The effects of CO2 laser spot size, laser irradiation time and laser power on plasma emission intensity were investigated. And on this basis, the variation of electron temperature and electron density of plasma with delay time is obtained.

Implementation of a thermomechanical model to simulate laser heating in shrinkage tissue (effects of wavelength, laser irradiation intensity, and irradiation beam area)

Advancements in the use of laser technology in the medical field have motivated the widespread use of thermal energy to treat a wide variety of diseases and injuries. During laser-induced thermotherapy, the tissue gains heat from laser irradiation and its shape is deformed due to non-uniform temperature distribution. To describe the phenomenon adequately, the mathematical model that considers both heat transfer and mechanical deformation is needed. In this study, the formulation of mathematical model describing coupled heat transfer and mechanical deformation of tissue subjected to laser-induced thermotherapy is numerically implemented. The effects of laser irradiation time, wavelength, laser intensity, laser beam radius and blood perfusion rate on temperature distribution, Von Mises stress distribution, and displacement of the layered skin during laser irradiation are systematically investigated. The values obtained provide an indication of limitations that must be considered in administering laser-induced thermotherapy.

Effect of vibration frequency and displacement on melt expulsion characteristics and geometric parameters for ultrasonic vibration-assisted laser drilling of steel

Recently, the applications of ultrasonic vibration assistance to laser-based manufacturing processes are rapidly proliferating. Ultrasonic vibration-assisted laser drilling (UVLD) process involves simultaneous application of high frequency vertical vibrations to the workpiece while being irradiated with a continuous wave laser beam. In UVLD, the ultrasonic vibration assistance causes expulsion of droplets from the laser melted surface, resulting in the formation of deep holes. In this paper, systematic analysis of the effects of ultrasonic vibration frequency (20–40 kHz) and displacement (16–32 µm) on melt expulsion characteristics in early stages of drilling and geometric/quality features of the holes for UVLD of AISI 316 is presented. Based on the analysis of initiation of droplet ejection from the melt pool and particle size of the ejected droplets, mechanisms of droplet ejection based on capillary wave theory are proposed. It was observed that while increasing both ultrasonic vibration frequency and displacement resulted in reduction in droplet ejection initiation time and the formation of deeper holes for the given laser irradiation time (100 ms), the effect of vibration displacement was much more pronounced than the frequency on the variation.

Near infrared low-level laser therapy and cell proliferation: The emerging role of redox sensitive signal transduction pathways.

Lasers devices are widely used in various medical fields (eg, surgery, dermatology, dentistry, rehabilitative medicine, etc.) for different applications, ranging from surgical ablation of tissues to biostimulation and pain relief. Laser is an electromagnetic radiation, which effects on biological tissues strongly depends on a number of physical parameters. Laser wavelength, energy output, irradiation time and modality, temperature and tissue penetration properties have to be set up according to the clinical target tissue and the desired effect. A less than optimal operational settings, in fact, could result in a null or even lethal effect. According to the first law of photobiology, light absorption requires the presence of a specific photoacceptor that after excitation could induce the activation of downstream signaling pathways. Low-level lasers operating in the red/near infrared portion of the light spectra are generally used for biostimulation purposes, a particular therapeutic application based on the radiant energy ability to induce nonthermal responses in living cells. Biostimulation process generally promotes cell survival and proliferation. Emerging evidences support a low-level laser stimulation mediated increase in "good" reactive oxygen species, able to activate redox sensitive signal transduction pathways such as Nrf-2, NF-kB, ERK which act as key redox checkpoints.

A paper-based photothermal array using Parafilm to analyze hyperthermia response of tumour cells under local gradient temperature.

Temperature is a critical extrinsic physical parameter that determines cell fate. Hyperthermia therapy has become an efficient treatment for tumor ablation. To understand the response of tumor cells under thermal shocks, we present a paper-based photothermal array that can be conveniently coupled with commercial 96-well cell culture plates. This paper chip device was fabricated in one step using Parafilm® and Kimwipers® based on a heat lamination strategy. Liquid was completely adsorbed and confined within the cellulose fibres of hydrophilic regions. Then, Prussian blue nanoparticles (PB NPs) as the photothermal initiator were introduced into the loading wells, and thermal energy was generated via near infrared (NIR) laser irradiation. After assembling the paper device with a 96-well plate, the temperature of each well could be individually controlled by varying the loading amount of PB NPs and laser irradiation time. As a proof-of-concept study, the effects of local thermal shocks on HeLa cells were investigated using MTT cell viability assay and Live/Dead cell staining. The variation of cell viability could be monitored in situ with controllable temperature elevation. The proposed paper photothermal array loaded with thermal initiators represents an enabling tool for investigating the hyperthermia responses of biological cells. Moreover, the facile fabrication technique for paper patterning is advantageous for customizing high-throughput microfluidic paper-based analytical devices (μPADs) with extremely low cost.

Synthesis of Bare Iron Nanoparticles from Ferrocene Hexane Solution by Femtosecond Laser Pulses.

Iron-based nanoparticles (FeNPs) have unique and attractive properties such as superparamagnetism, biocompatibility, and catalytic activity. Although the synthesis of precious metal NPs from a metal in liquid and/or metal salt solution by a pulsed laser has been investigated, comparably little effort has been devoted to examine the production of FeNPs. Here we report the synthesis of carbon-shell free spherical NPs of iron oxide (magnetite) from ferrocene hexane solution by femtosecond near infrared laser pulses. Nanosecond UV laser pulses are used to compare the evolution of the particle size distribution as a function of laser irradiation time. The size of NPs remains constant even for extended exposure to femtosecond laser pulses, whereas it grows with exposure to nanosecond laser pulses. The primary particles are generated by photochemical reactions regardless of pulse duration; however, the fragmentation of NPs by successive femtosecond laser pulses regulates the particle size.

Femtosecond-laser-induced submicron grating periodic structures on As2S3 and As35Se65 glasses

Submicron periodic structures produced by femtosecond Ti:sapphire laser irradiation (1 kHz, 150 fs, 3–5 μm) on As2S3 and As35Se65 glasses at edges of damage holes are observed. Effects of changes in laser wavelength (λ), pulse number, power, and irradiation time on grating periodicity were studied. Regular groove-like ripples and distinct parallel submicron periodic gratings were seen in damaged areas. The damage grating period (Λ) is approximately λ/2n. The period increases with wavelength but is hardly influenced by irradiation time and pulse number. Samples with high refractive index and low bandgap are more prone to melting, and edge stripes are not obvious.

Spatially resolved optical activation of Eu ions by laser irradiation in implanted hexagonal MoO3 microrods

An effective optical activation of Eu ions in implanted h-MoO3 microrods can be achieved by ultraviolet (325 nm) or red (633 nm) laser irradiation in a confocal microscope, contrary to the case of rapid thermal annealing or conventional annealing treatments. Eu3+ photoluminescence emission is triggered by h-MoO3 to α-MoO3 or h-MoO3 to η-Mo4O11 phase transformations induced by the laser beam, as revealed by Raman microscopy and spectroscopy. The formation of such phases was found to depend on laser wavelength, power density, and irradiation time. The possibility to induce controlled activation of luminescent rare earth ions at a desired position and with high precision by laser irradiation is of interest for potential applications of this material in optoelectronics.

Hybrid spray-coating, laser-scribing and ink-dispensing of graphene sensors/arrays with tunable piezoresistivity for in situ monitoring of composites

Graphene based nanotechnology has offered a variety of novel strategies for enabling self-sensing and diagnosing functionalities for next-generation composites. In comparison to traditional methods with complicated procedure and limited scalability, a new process is impending for graphene sensor fabrication with designable shape and controllable performance. Toward this goal, this paper combined multiple computer-aided processes for designing graphene thin film sensors and arrays on composites, including spray-coating, laser-scribing and ink-dispensing. The processing-structure-property relationship was systematically investigated for understanding the piezoresistive performance of the laser scribed graphene (LSG) sensors. It is determined that by increasing the cycle time of laser irradiation, the gauge factor could be tailored up to 3 orders of magnitude from ∼450 to ∼0.6. The accumulated bump-shaped structure originated from intenser reduction of graphene oxide (GO) is believed to disrupt the efficiency of load-transfer and degrade the resulting performance. With the optimized recipe, versatility of LSG sensors and arrays deployed with ink-printed circuits was further explored for monitoring and mapping large-scale deformation and strain distribution of polymeric composites.

ESTUDIO DE LOS EFECTOS PROVOCADOS POR LA RADIACIÓN DEL LÁSER DE CO2 EN LA DOLOMITA NATURAL, PARA LA DEGRADACIÓN DEL COLORANTE REACTIVO NEGRO 5 UTILIZANDO LA TÉCNICA DE FOTOCATALISIS

In the present work, the changes in the natural dolomite produced by calcination with CO2 laser was analyzed, the power density and irradiation time of the CO2 laser were varied. The characterization of each sample in terms of changes produced by radiation was obtained. For this, a mineral analysis was carried out by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD). The EDS analysis revealed the presence of elements such as Mg, Si, Al, Ca, O, Fe, Z and Na, while the X-ray diffraction analysis suggested that the treated dolomite samples experienced slight changes in their crystalline structure when they were calcined with the CO2 laser, however, there were no changes in the main phase of the dolomite but there was a decrease in the intensities of the signals. Additionally, a photocatalytic study was performed on the degradation of the Azo dye Reactive Black 5 (RB5) in an acid aqueous medium using natural dolomite and natural dolomite calcined with the CO2 laser. UV / VIS spectrophotometry was used for the characterization of the photocatalytic tests. An increase in the degradation and decolorization speed of the Black 5 dye was observed.

Investigation of laser-irradiated structure evolution and surface modification by in situ Micro-Raman spectroscopy

The structure evolution and surface modification of the ZnSb, ZnSb-Bi and ZnSb-NiO phase-change films are detected by in situ Raman laser irradiation with the different laser power and irradiation time. The results show that undoped ZnSb films exhibit a phase transformation from amorphous to metastable phases at 250 mW. The Bi-doped ZnSb films exhibit two different crystallization behaviors as the laser power increases. The films containing low Bi-doping concentration exhibit an amorphous-to-metastable phase transition, while the films containing high Bi-doping concentration directly crystallize into a mixture of new Bi-related crystalline phases and metastable ZnSb phases. As for ZnO-doped ZnSb films, the structure evolution encounters an amorphous phase, metastable ZnSb phase or mixture of both. Identifying the structure evolution in the metastable phase by in-situ Raman measurement method is of great significance for phase change memory application.

Surface modification of single-crystalline silicon carbide by laser irradiation for microtribological applications

Carbide-derived carbon layers were locally formed on the surface of 4H-SiC single crystalline wafers by irradiation with an infrared laser (λ = 9.3 μm) in a low vacuum. Longer laser irradiation time produced thicker carbon layers and improved the bonding continuity. For an irradiation duration of 4.5 s, the modified layer was formed without surface damage and identified as amorphous carbon containing gradient amount of Si with a layer thickness of several nm. The results of friction tests conducted on the modified layer under micro-loads using a friction force microscope revealed the improvement of lubricity of the modified layer with a friction coefficient of 0.01 that is lower than that of the original SiC surface. No wear tracks were detected after scanning the Si probe over the layer surface 10,000 times with maintaining lubricity. The layer also preserved its lubricity after heating up to 550 °C in an air atmosphere; however, the lubricity disappeared at 600 °C owing to decomposition of the lubricating layer caused by oxidation.