Laser Exposure Time Research Articles

Photoluminescence Intensity Enhancement in Poly(3-thiopheneacetic Acid) Films Induced by Laser Irradiation

In this work, we have reported an enhancement of the photoluminescence intensity in Poly(3-thiopheneacetic acid), PTAA, films irradiated by laser in air. This effect depends on the laser intensity, exposure time and sample thickness. It was observed an increase of the luminescence intensity up to 110% without any significant shift in PL peak position. Our results suggest that a partial degradation process occurs in the sample, which confines the charge carriers in a narrower region of the film increasing the probability of radioactive decay.

A PRACTICAL MOIRÉ INTERFEROMETRY SYSTEM FOR TESTING MACHINE APPLICATIONS

A variety of experiments were performed on a 60,000-lb-capacity testing machine using a compact moire inter-ferometry system with high displacement sensitivity. High loads and test versatility were achieved. Quality fringe patterns were obtained using a low-power laser and short exposure times.

Femtosecond Laser Photodisruption of Porcine Anterior Chamber Angle: an Ex Vivo Study

The femtosecond laser is a promising tool for the micromachining of biological tissues. The current study investigated the feasibility of noninvasive glaucoma therapy by femtosecond laser ablation in enucleated porcine eyes by delivering the laser energy through a gonioscopic lens. Freshly enucleated porcine eyes were kept in Optisol GS solution (Bausch & Lomb, Rochester, NY) at 4 degrees C for up to 48 hours. Photodisruption was attempted at the peripheral inner surface of the cornea using a gonioscopic lens and a custom femtosecond laser ablation system. Femtosecond laser ablation was performed using a Ti:Sapphire laser (800-nm wavelength) focused with a 0.15 numerical aperture lens. The laser treatment process was recorded by real time video and the lesions were examined histologically. During laser surgery, bubble formation was observed and appeared to be positively related to laser energy and exposure time. When examined histologically, areas of ablation were consistently observed at the peripheral inner surface of the cornea. The extent of the lesion increased nonlinearly with both pulse energy and exposure time, showing saturation at high energy and long times. For a given energy dose, fewer pulses of high energy were more effective than many low energy pulses. The current study demonstrates that laser ablation at the anterior chamber angle is feasible by a femtosecond laser ablation system using a gonioscopic lens in ex vivo eyes. The results indicate the potential of a novel noninvasive glaucoma laser therapy.

Thermal and optical properties of AgSbS2 thin films prepared by pulsed laser deposition (PLD)

Thin amorphous AgSbS2 films were deposited as the potential candidate for new phase-change memory material. Thin films were prepared by pulsed laser deposition (PLD) from AgSbS2 polycrystalline bulk samples. Bulk samples were prepared by melt-quench technique from pure elements. Composition and chemical homogeneity of these bulks were checked by scanning electron microscopy with energy dispersive analysis (SEM-EDX); the crystallinity was studied by X-ray diffraction (XRD). Prepared thin films were characterized by electron microprobe SEM-EDX (composition, chemical homogeneity, surface morphology), differential scanning calorimetry DSC (crystallization temperature Tc, phase transformation temperature TLT→HT and melting temperature Tm) and by UV–Vis–NIR spectroscopy (film thickness d, spectral dependence of refractive index n, single oscillator energy E0, dispersion energy Ed, and optical band gap energy Egopt values). The phase-change recording process in amorphous AgSbS2 thin films was tested via photocrystallization experiments done by Ar+ ion laser. The laser exposed dots were studied by scanning electron microscopy (SEM) and transmission optical microscopy. Micro X-ray diffraction (μ-XRD) was used for exposed dot crystallinity study. The kinetics of phase transition was traced by measurement of optical transmission in dependence on laser exposure time (photocrystallization kinetic curve).

The antimicrobial efficacy of the erbium, chromium:yttrium-scandium-gallium-garnet laser with radial emitting tips on root canal dentin walls infected with Enterococcus faecalis

The authors used an in vitro model to investigate the ability of an erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser with radial emitting tips to disinfect Enterococcus faecalis-infected dentin. The in vitro infected-dentin model system consisted of a dentin cylinder, prepared from a human anterior tooth root, cemented into a sealable two-chamber device fabricated from a syringe needle cap. The model's lower chamber contained a buffer solution, and the dentin cylinder was placed between the upper and lower chambers. After sterilization, the authors inoculated the root canal of each dentin cylinder with E. faecalis. They used an Er,Cr:YSGG laser with radial emitting tips to irradiate the root canal of each infected dentin cylinder (varying laser power and exposure time). After laser treatment, the authors machined the root canal dentin walls and collected the resulting dentin fillings in the buffer-reservoir. They quantified the E. faecalis titer of each buffer-reservoir by using selective agar plates. The authors found that bacterial recovery decreased when laser irradiation duration or power increased. A greater degree of disinfection was achieved with a 120-second application of laser than with sodium hypochlorite treatment. Finally, they found that a 99.7 percent reduction in bacterial counts could be obtained using the laser. The results of this study suggest that the Er,Cr:YSGG laser with a radial emitting tip has a significant antimicrobial effect on dentinal tubules infected with E. faecalis. Er,Cr:YSGG laser treatment could be a valuable tool for root canal disinfection during endodontic treatment.

Analysis of Nd:YAG laser‐mediated thermal damage in rabbit nasal septal cartilage

Laser cartilage reshaping (LCR) involves the use of photo-thermal heating to reshape cartilage. Its clinical relevance depends on the ability to minimize thermal injury in irradiated regions. The present study seeks to understand the safety of LCR by determining shape change and resultant tissue viability as a function of laser dosimetry. Rabbit nasal septal cartilage were irradiated using a Nd:YAG laser (lambda = 1.32 microm, 5.4 mm spot diameter) with different exposure times of 4, 6, 8, 10, 12, and 16 seconds and powers of 4, 6, and 8 W. Temperature on the cartilage surface in the laser-irradiated region was collected using infrared thermography, this data was then used to predict tissue damage via a rate process model. A Live/Dead viability assay combined with fluorescent confocal microscopy was used to measure the amount of thermal damage generated in the irradiated specimens. Considerable thermal injury occurred at and below the laser-reshaping parameters that produced clinically relevant shape change using the present Nd:YAG laser. Confocal microscopy identified dead cells spanning the entire cross-sectional thickness of the cartilage specimen (about 500 microm thick) at laser power density and exposure times above 4 W and 6 seconds; damage increased with time and irradiance. The damage predictions made by the rate process model compared favorably with measured data. These results demonstrate that significant thermal damage is concurrent with clinically relevant shape change. This contradicts previous notions that there is a privileged laser dosimetry parameter where clinically relevant shape change and tissue viability coexist.

Quantifying RhoA Facilitated Trafficking of the Epithelial Na+ Channel toward the Plasma Membrane with Total Internal Reflection Fluorescence-Fluorescence Recovery after Photobleaching

The epithelial Na(+) channel (ENaC) plays a central role in control of epithelial surface hydration and vascular volume. Similar to other ion channels, ENaC activity is set, in part, by its membrane levels. The small G protein RhoA increases ENaC activity by increasing the membrane levels of this channel. We hypothesize that RhoA increases ENaC activity by promoting channel trafficking to the plasma membrane. Few experimental methods are available to directly visualize trafficking of ion channels to the plasma membrane. Here we combine electrophysiology with two complementary imaging methods, total internal reflection fluorescence microscopy and fluorescence recovery after photobleaching, to study the mechanistic basis of RhoA actions on ENaC. Patch clamp results demonstrate that RhoA increases ENaC activity in an additive manner with dominant-negative dynamin. This is consistent with a mechanism of increased ENaC trafficking to the membrane. Direct visualization of ENaC movement near the plasma membrane with total internal reflection fluorescence-fluorescence recovery after photobleaching revealed that RhoA accelerates ENaC trafficking toward the membrane. RhoA-facilitated movement of the channel was sensitive to disrupting the endomembrane system. Moreover, facilitating retrieval decreased ENaC activity but not trafficking toward the membrane. ENaC at the plasma membrane clustered and was laterally immobile suggesting that the cytoskeleton tethers or corrals membrane resident channels or membrane-directed vesicles containing ENaC. Disrupting microtubules but not microfilaments led to reorganization of ENaC clusters and slowed trafficking toward the membrane. The cytoskeleton is an established target for RhoA signaling. We conclude that RhoA, likely through effects on the cytoskeleton, promotes ENaC trafficking to the plasma membrane to increase channel membrane levels and activity.

Influence of silver concentration in Agx(Sb0.33S0.67)100−x thin amorphous films on photoinduced crystallization

One of the recent applications of thin chalcogenide films is in rewritable optical data recording. This technology is based on reversible phase transition between crystalline and amorphous state. Currently, the primary materials for rewritable optical are Ge–Sb–Te and Ag–In–Sb–Te alloys, but materials research still continues due to the need for increased storage capacity and data recording rates. (Ag)–Sb–S thin films were prepared by thermal evaporation of Sb33S67 bulk and optically induced diffusion and dissolution of thermally evaporated Ag films. Prepared samples were characterized by electron microprobe (SEM-EDX), differential scanning calorimetry (DSC) and by UV–Vis–NIR and Raman spectroscopy. The phase-change recording processes in (Ag)–Sb–S films were carried out by photocrystallization experiments done by Ar+ ion laser. The laser exposed dots were studied by scanning electron microscopy (SEM) and transmission optical microscopy. Micro X-ray diffraction (μ-XRD) was used for the exposed dots crystallinity study. Photocrystallization kinetic curves (showing the dependence of optical transmission on laser exposure time) were also established. Crystallization mechanism of Agx(Sb0.33S0.67)100−x samples was discussed.

Theoretical analysis of thermal damage in biological tissues caused by laser irradiation.

A bioheat transfer approach is proposed to study thermal damage in biological tissues caused by laser radiation. The laser light propagation in the tissue is first solved by using a robust seven-flux model in cylindrical coordinate system. The resulting spatial distribution of the absorbed laser energy is incorporated into the bioheat transfer equation for solving temperature response. Thermal damage to the tissue is assessed by the extent of denatured protein using a rate process equation. It is found that for the tissue studied, a significant protein denaturation process would take place when temperature exceeds about 53 degrees C. The effects of laser power, exposure time and beam size as well as the tissue absorption and scattering coefficients on the thermal damage process are examined and discussed. The laser conditions that cause irreversible damage to the tissue are also identified.

Optical Memory in DuPont Photopolymers by Using Femtosecond Laser Pulses

To investigate the feasibility of a high density optical memory in photopolymers, we used twophoton absorption of near-infrared femtosecond laser pulses to perform bit-wise three-dimensional storage. We monitored the transmitted probe beam, which was modulated by the change of refractive index caused by the femtosecond laser irradiation. The size of the spots generated by the focused Gaussian beam depended on the laser intensity and exposure time. The minimum lateral and longitudinal sizes of a spot were estimated as 0.5 and 5 μm, respectively.

The detection of laser-induced structural change of MnO 2 using in situ Raman spectroscopy combined with self-modeling curve resolution technique

In this paper, we present the use of one of the self-modeling curve resolution techniques, band-target entropy minimization (BTEM), which is independent of any spectral library, to elucidate Raman pure component spectra of two different manganese oxides arising from laser-induced structural changes. It is often extremely difficult to obtain the pure Raman spectrum of MnO 2 without changing it to another structural form. However, using BTEM to analyze the collected in situ Raman spectra measured as a function of laser exposure time, has enabled us to obtain both the pure component spectra of the original sample and the product due to laser irradiation. This technique proves to be an efficient Raman spectral interpretation method for thermal sensitive solid samples.

Acoustic Estimation of Thermal Distribution in the Vicinity of Femtosecond Laser-Induced Optical Breakdown

Laser-induced optical breakdown (LIOB), or photo-disruption, can generate individual microbubbles in tissues for biomedical applications. We have previously developed a co-localized high-frequency ultrasound system to detect and characterize these laser-induced microbubbles. Because ultrasound speed varies with temperature, this system can also be used to directly estimate thermal effects in the vicinity of photodisruption. In this study, individual bubbles (sizes 60-100 microm) were created at the bottom of a water tank using a 793-nm, 100-fs Ti:Sapphire laser pulsed at 250 kHz. During and after breakdown, pulse-echoes from the tank bottom in the region surrounding a bubble were recorded with a single-element 85-MHz ultrasonic transducer, and temperature-dependent pulse-echo displacements were calculated using phase-sensitive correlation tracking. These displacements were then fit to a finite-element heat transfer model to estimate the effective thermal distribution. Estimates were calculated for laser exposure times ranging from 6.25 to 312.5 ms (1600 to 78 000 laser pulses), at 1.5 and 4 J/cm2 fluences. Results suggest a minimal temperature increase (<1 degrees C) within 100 microm of a bubble created with <1600 laser pulses at 1.5 J/cm2 fluence. This implies that LIOB can be controlled to be thermally noninvasive in the bubble vicinity.

Surface nanostructuring by femtosecond laser irradiation through near-field scanning optical microscopy

A near-field scanning optical microscopy (NSOM) and a double-frequency femtosecond laser (400 nm, 100 fs) were applied to push the optical resolution further down to sub-50 nm on thin UV photoresist. A 20-nm feature size can be obtained. It is at a resolution of λ/20 ( λ: laser wavelength) and a/2 ( a: NSOM probe aperture diameter), respectively. It is proved that laser power and exposure time can affect feature size of lithography patterns. In this paper, the effect of probe-to-sample distance on dot-pattern features is studied, and different dot-pattern shapes are generated: dumbbell-dot, ellipsoid-dot and circle-dot. The simulated light field spatial distributions across the nano-aperture based on Bethe–Bouwkamp model is found to agree with experimental results very well.

Defects related to N-sublattice damage in electron irradiated GaN

Defects related to the N-sublattice of GaN are studied with electron irradiation. Selective damage of the N-sublattice is achieved by irradiating the samples with 0.42 MeV electrons. A new shallow donor B 1 with binding energy of 24.9±0.4 meV was found after irradiation with ground state bound exciton emission at 3.4732 eV. Among the possible defects, the nitrogen vacancy (V N) is the most likely candidate for the new donor B 1. In addition, an interesting change in the excitonic luminescence of the irradiated sample is observed under focused 267 nm laser beam illumination at cryogenic temperatures. The intensities of O NX A and Si GaX A, the total band edge luminescence intensity, and the luminescence decay lifetime of free and bound excitons all increase with laser exposure time, and the relative intensity of the B 1-bound exciton emission decreases. This effect is not observed with below bandgap illumination. We propose that this reflects the light-induced dissociation of non-radiative defect complexes of O N and Si Ga with N i, subsequently the migration of N i and then at least partial annihilation of N i with V N. The new donor B 1-bound exciton emission and the light-induced instability start to disappear upon annealing around 300 °C, indicating the thermal dissociation of donor–nitrogen complexes and annihilation of the irradiation-induced vacancy- and interstitial-type defects.

Femtosecond laser-induced reduction in Eu-doped sodium borate glasses

In this work, we report permanent reduction of Eu 3+ to Eu 2+ in sodium borate glasses by irradiation of near-infrared femtosecond laser. Glass composition of sodium borate was 85B 2O 3–15Na 2O. The glasses were doped with 0.05, 0.1, and 0.5 mol% Eu 2O 3. Absorption and fluorescence dynamics were studied to investigate valence state change of europium ions and the energy transfer between Eu 2+ and Eu 3+ ions. As the femtosecond laser intensity or exposure time increases, the emission band at 400 nm becomes stronger. However, the photoreduction efficiency decreases as the dopant concentration increases. We discuss the photoreduction mechanism under multiphoton absorption.

Luminescence properties of femtosecond-laser-activated silver oxide nanoparticles embedded in a biopolymer matrix

Strong visible luminescence is observed from silver clusters generated by femtosecond-laser-induced reduction of silver oxide nanoparticles embedded in a polymeric gelatin matrix. Light emission from the femtosecond-laser-activated matrix areas considerably exceeds the luminescence intensity of similarly activated bare silver oxide nanoparticle films. Optical spectroscopy of the activated polymer films supports the assignment of the emissive properties to the formation of small silver clusters under focused femtosecond-laser irradiation. The size of the photogenerated clusters is found to sensitively depend on the laser exposure time, eventually leading to the formation of areas of metallic silver in the biopolymer matrix. In this case, luminescence can still be observed in the periphery of the metallic silver structures, emphasizing the importance of the organic matrix for the stabilization of the luminescent nanocluster structures at the metal–matrix interface.

Effect of laser and environmental parameters on reducing microbial contamination of stainless steel surfaces with Nd:YAG laser irradiation

The effect of laser (pulse repetition frequency, pulse energy and exposure time) and environmental parameters (pH, NaCl concentration and wet or dry samples) of Nd:YAG laser decontamination of stainless steel inoculated with Escherichia coli, Staphylococcus aureus and Listeria monocytogenes was investigated. Stainless steel discs were inoculated with the bacterial samples and exposed to laser energy densities to about 900 J cm(-2). These inactivation curves allowed selection of laser parameters for two-level multifactorial designed experiments, the results of which allowed comparisons to be made between effects of individual and combined parameters on the laser inactivation efficiency. Escherichia coli was inactivated most effectively as a wet film with L. monocytogenes and S. aureus showing similar response. For the multifactorial experiments all laser parameters were significant and were smallest for S. aureus as a wet film. pH and NaCl concentration had little effect on the efficacy of laser inactivation but dry or wet states and all laser parameters were significant. Such systems may prove to be applicable in industrial processes where stainless steel may be contaminated with acidic solutions or salt, e.g. in the food industry with laser inactivation seeming to be independent of these parameters. Parameters have been identified that allow optimization of the treatment process.

A Numerical Method for Optimizing Laser Power in the Irradiation of a 3-D Triple-Layered Cylindrical Skin Structure

ABSTRACT It is of interest to research hyperthermia combined with radiation and cytotoxic drugs to enhance the killing of tumors. The crucial problem is to keep surrounding normal tissue below a temperature that will produce harm when heating the tumor tissue. In this study, we develop a numerical model for optimizing laser power in the irradiation of a 3-D triple-layered cylindrical skin structure. The method determines the required laser intensity in order to obtain prespecified temperatures at given locations on the skin surface after a prespecified laser exposure time.

극미세 3차원 형상의 정밀제작을 위한 이광자 흡수 광중합 공정의 레이저 출력-조사시간 제어방법

극미세 3차원 형상의 정밀제작을 위한 이광자 흡수 광중합 공정의 레이저 출력-조사시간 제어방법

Clean Production of Hydrogen via Laser-Induced Methane Conversion

A novel technique based on the multi-photon dissociation of methane for hydrogen production has been developed. The study was carried out with a simple setup using UV laser radiation at 355 nm wavelength. The hydrogen yield achieved at ambient temperature and one atmospheric pressure is 6.6 mole %. The conversion process of methane to produce hydrogen was investigated under different experimental parameters such as laser exposure time, laser power, and methane pressure. The quantum efficiency of these processes was also estimated. The maximum quantum efficiency of 42% was attained for 30 minutes of laser exposure of methane at 1 atmospheric pressure.