Effect Of Laser Exposure Research Articles

Finite element model of the temperature increase in excised porcine cadaver iris during direct illumination by femtosecond laser pulses

In order to model the thermal effect of laser exposure of the iris during laser corneal surgery, we simulated the temperature increase in porcine cadaver iris. The simulation data for the 60 kHz FS60 Laser showed that the temperature increased up to 1.23°C and 2.45°C (at laser pulse energy 1 and 2 [micro sign]J, respectively) by the 24 second procedure time. Calculated temperature profiles show good agreement with data obtained from ex vivo experiments using porcine cadaver iris. Simulation results of different types of femtosecond lasers indicate that the Laser in situ keratomileusis procedure does not present a safety hazard to the iris.

Accelerated alpha decay under laser exposure of metallic nanoparticles in aqueous solutions of uranium salt

The recent experimental results on the acceleration of alpha decay under laser exposure of metallic nanoparticles in aqueous solutions (D2O or H2O) of uranium salt UO2Cl2 are reviewed. It is demonstrated that the rate of the alpha decay of uranium branching depends on the laser wavelength and laser peak power both under exposure of the solution of uranium salt in colloidal solutions of metallic nanoparticles and under laser ablation of a bulk target in an aqueous solution. Tuning the laser wavelength to the plasmon resonance allows observation of large deviations of the contents of radio-nuclides of 238U branching from their equilibrium values. The effect of laser exposure is characterized by high isotopic selectivity towards the decay of different nuclides. Possible mechanisms of the laser-induced alpha decay of uranium isotopes and their potential applications are discussed.

Nanoporous titania films produced by pulsed interference lithography

We describe a simple, inexpensive technique for producing deep nanopores on the surface of titania films using laser exposure in a four-beam interference configuration. In addition to producing nanopores, laser pulses convert amorphous titania films to a polycrystalline state. The effect of laser exposure on the TiO2 surface can be used to improve its biophotocatalytic properties, optimise solar cells, etc.

Effects of near‐infrared laser exposure in a cellular model of wound healing

Clinical studies have demonstrated beneficial outcomes for low-level laser therapy (LLLT) using near-infrared (NIR) wavelengths. It has been hypothesized that the benefits of NIR LLLT are due in part to the thermal effects of NIR exposure. However, it is not clear whether photochemical interactions between NIR light and superficial tissues contribute to beneficial outcomes. To investigate the photochemical effects of NIR exposure, the efficacy of 980 nm NIR LLLT on human fibroblast growth rates is investigated using an in vitro model of wound healing. A small pipette is used to induce a wound in fibroblast cell cultures, which are imaged at specific time intervals over 48 h and exposed to a range of laser doses (1.5-66 J/cm(2)) selected to encompass the range of doses used during other in vivo and in vitro studies. For each image acquired, wound sizes were quantified using a novel application of existing image processing algorithms. Cell growth rates were compared across different laser exposure intensities with the same exposure duration, and across different laser exposure durations with the same exposure intensity. Exposure to low- and medium-intensity laser light accelerates cell growth, whereas high-intensity light negated the beneficial effects of laser exposure. Cell growth was accelerated over a wide range of exposure durations using medium-intensity laser light, with no significant inhibition of cell growth at the longest exposure durations used in this study. Low-level exposure to 980 nm laser light can accelerate wound healing in vitro without measurable temperature increases. However, these results also demonstrate the need for appropriate supervision of laser therapy sessions to prevent overexposure to NIR laser light that may inhibit cell growth rates observed in response to lower intensity laser exposure.

Comparison of light intensity on the brain surface due to laser exposure during optical topography and solar irradiation

Optical topography (OT), which is based on the near-infrared spectroscopy, is a powerful tool for observing brain activity noninvasively. To estimate the effect of laser exposure on the brain, photon-distribution profiles in bald heads of adults and neonates during the OT were calculated using the photon-diffusion equation. These calculations showed that although the absolute values of the intensity depend on details of the head model, the relative values of OT exposure to sunlight exposure were less sensitive to the model details. As an example, the light intensities on the brain surface during OT obtained by using a commercially available system were about 2% for adults and 3% for neonates of those values obtained under midday sunlight on a sunny day in midsummer. These values were obtained under the reasonable assumptions with a large safety factor.

WAVELENGTH DEPENDENCE OF OCULAR DAMAGE THRESHOLDS IN THE NEAR-IR TO FAR-IR TRANSITION REGION: PROPOSED REVISIONS TO MPES

This report summarizes the results of a series of infrared (IR) laser-induced ocular damage studies conducted over the past decade. The studies examined retinal, lens, and corneal effects of laser exposures in the near-IR to far-IR transition region (wavelengths from 1.3-1.4 mum with exposure durations ranging from Q-switched to continuous wave). The corneal and retinal damage thresholds are tabulated for all pulsewidth regimes, and the wavelength dependence of the IR thresholds is discussed and contrasted to laser safety standard maximum permissible exposure limits. The analysis suggests that the current maximum permissible exposure limits could be beneficially revised to (1) relax the IR limits over wavelength ranges where unusually high safety margins may unintentionally hinder applications of recently developed military and telecommunications laser systems; (2) replace step-function discontinuities in the IR limits by continuously varying analytical functions of wavelength and pulsewidth which more closely follow the trends of the experimental retinal (for point-source laser exposures) and corneal ED50 threshold data; and (3) result in an overall simplification of the permissible exposure limits over the wavelength range from 1.2-2.6 mum. A specific proposal for amending the IR maximum permissible exposure limits over this wavelength range is presented.

The application of Raman and anti-stokes Raman spectroscopy for in situ monitoring of structural changes in laser irradiated titanium dioxide materials

The use of Raman and anti-stokes Raman spectroscopy to investigate the effect of exposure to high power laser radiation on the crystalline phases of TiO 2 has been investigated. Measurement of the changes, over several time integrals, in the Raman and anti-stokes Raman of TiO 2 spectra with exposure to laser radiation is reported. Raman and anti-stokes Raman provide detail on both the structure and the kinetic process of changes in crystalline phases in the titania material. The effect of laser exposure resulted in the generation of increasing amounts of the rutile crystalline phase from the anatase crystalline phase during exposure. The Raman spectra displayed bands at 144 cm −1 (A1g), 197 cm −1 (Eg), 398 cm −1 (B1g), 515 cm −1 (A1g), and 640 cm −1 (Eg) assigned to anatase which were replaced by bands at 143 cm −1 (B1g), 235 cm −1 (2 phonon process), 448 cm −1 (Eg) and 612 cm −1 (A1g) which were assigned to rutile. This indicated that laser irradiation of TiO 2 changes the crystalline phase from anatase to rutile. Raman and anti-stokes Raman are highly sensitive to the crystalline forms of TiO 2 and allow characterisation of the effect of laser irradiation upon TiO 2. This technique would also be applicable as an in situ method for monitoring changes during the laser irradiation process.

Determining optimal dose of laser therapy for attachment and proliferation of human oral fibroblasts cultured on titanium implant material

The purpose of this study was to investigate the influence of single or multiple doses of low-level laser therapy (LLLT) on attachment and proliferation of human gingival fibroblasts in a standardized, reproducible in vitro model. Titanium discs were randomly allotted to one of three groups: group I served as a control, group II was exposed to a single laser dose of 3 J/cm2, and the three subgroups in group III were exposed to laser doses of 0.75, 1.5, and 3 J/cm2. To examine the possible thermal effects of laser exposure on the cell culture, the temperature in the Petri dish was measured for every dose used, before and during irradiation. For attachment assays, groups II and III were exposed to laser irradiation and then seeded onto titanium discs. In group III, the exposures were repeated after 3 and 6 h. Cells were cultured for 6 and 24 h and stained with Hoechst and Propidium. Attached cells were counted under a light microscope. To investigate the effect of LLLT on cell proliferation after 48 h, 72 h, and 7 days, cells were cultured on titanium discs for 24 h and then exposed to laser irradiation for 1 day and 3 consecutive days, respectively. Cell proliferation was determined by counting cells under the microscope and by a cell proliferation enzyme-linked immunosorbent assay system. No increase of temperature of the cell cultures occurred before or during laser exposure at any of the doses tested. Both single and multiple doses of LLLT significantly enhanced cellular attachment (p<0.05). The proliferation assays showed higher cell proliferation (p<0.05) in group III at doses of 1.5 and 3 J/cm2 after 72 h and 7 days, with agreement between staining and enzyme-linked immunosorbent assay. It is concluded that, in this cellular model, the attachment and proliferation of human gingival fibroblasts are enhanced by LLLT in a dose-dependent manner.

Some aspects of the stability of ion current in a matrix-assisted laser desorption/ionization source.

The effect of laser exposure (the number of laser shots) on the stability of production of matrix (gentisic acid, sinapinic acid, nicotinic acid and benzoic acid) and biomolecule (insulin and cytochrome-c) ions is presented. Two methods of sample preparation, dried-droplet and pressure, were examined. In the case of pressure preparation, the dry powder sample was pressed mechanically with a pressure of 30 MPa. The best results were obtained for the pressure method and gentisic acid as matrix.

Changes in Semiconductor Prorerties under Laser Irradiation

The effect of laser exposure on semiconducting materials is studied. Using experimental data processing for silicon as an example, moderate laser fluxes (<106 W/cm–2) are shown to cause a sharp increase in the absorption coefficient of the surface semiconducting layer.

Crystallite size dependence of volatilization in matrix-assisted laser desorption ionization

During the desorption and ionization processes in matrix-assisted laser desorption ionization (MALDI), the laser beam interacts with different areas of the polycrystalline sample surface varying in crystal size and structure. CCD imaging of dried-droplet and electrospray deposited MALDI samples was used to explore the effect of laser exposure on surface morphology at atmospheric pressure. Crystal size distributions of the sinapinic acid target were examined prior to and after laser irradiation. Image processing and analysis of the difference images revealed the morphological changes in the sample. The results indicate that near-threshold irradiance smaller crystals (∼2 μm) are completely volatilized by the laser shot, whereas larger crystals undergo layer-by-layer evaporation (peeling). Heat conduction simulations in a finite slab have demonstrated that under similar conditions, the surface temperature of small crystallites increases markedly compared to their larger counterparts. These higher surface temperatures can lead to the selective volatilization of smaller crystallites. This study points to the influence of sample preparation on the crystal size distribution and its consequence on volatilization in MALDI-mass spectrometry (MS).

Damage to dental composite restorations following exposure to CO2 laser radiation.

Damage to tooth structure is a major hazard in the use of infrared lasers for oral surgical procedures. While the effects of laser exposure on dental enamel and dentine are well characterized, there are no data on the effects of laser exposure on dental composite materials, which are widely used in tooth-colored restorations. This study examined surface changes in several dental composites exposed to CO2 laser radiation for 200 msec. Surface changes, such as ablation, combustion, and melting, occurred even at relatively low power densities (340 W/cm2), with greater effects occurring in composites than in "compomers" (glass iomomer-composite mixtures). These findings indicate that nonmetallic dental restorations are prone to damage from inadvertent laser exposure. Clinicians must be aware of this hazard and employ measures to protect both natural tooth structure and restorations when performing intraoral laser surgery.

Visual functional changes associated with low-level light effects.

Development of more sensitive human clinical visual function tests is required for early detection of both acute and chronic laser exposure effects. Detection of low-level laser light exposure depends upon the measure of visual function employed. Visual function measures may reflect physiological processes at the retina as well as those at higher visual cortical centers. This paper focuses on the complexity of these measures through review of various experimental investigations using a variety of different measures to correlate retinal and functional alteration.

Chronic Laser Exposure Effects on Rabbit Retina

Dutch-belted 1 to 2.5 kg anesthetized rabbits were exposed to either xenon or argon laser light administered in a broad band, designed to cover large areas of the retina. For laser exposure, the pupil was dilated with atropine sulfate 1% and pheny lephrine 10%. All of the laser generated power was within a band centered at 5145.0 Anstroms. Established threshold for 4 hour exposures to laser irradiation are in the order of 25-35 microwatts/cm2. Animals examined for ultrastructural changes received 4 hour threshold doses. These animals exhibited ERG, opthalmascopic, and histological changes consistent with threshold damage.One month following exposure the rabbits were killed with pentobarbitol. The eyes were immediately enucleated and dissected while bathed in 3% phosphate buffered gluteraldehyde.