Nanosecond Pulsed Irradiation Research Articles

Study of Generation of Singlet Oxygen in Human Saliva <i>in vitro</i> Under the Action of Nanosecond Pulsed Laser Radiation

Background. The development of new laser devices for use in the treatment of complex dental pathology and microsurgery of the oral cavity with unique parameters with the ability to generate nanosecond pulsed radiation in a quasi-monochromatic radiation band is necessary. The high peak output power per pulse allows laser light to penetrate deeper into biological media without significant heating. The possibility of excitation of singlet oxygen without the use of endogenous photosensitizers is an indisputable advantage of such laser generators.
 Aims study of singlet oxygen generation in human oral fluid in vitro depending on the parameters of nanosecond pulsed laser radiation with a wavelength of ~1265 nm.
 Methods. We used a laser device with a main infrared (IR) emitter with a wavelength approximately corresponding to the oxygen absorption maximum (~1265 nm) with the generation of nanosecond pulsed radiation. A study was carried out to study the generation of singlet oxygen in the human oral fluid and the washing out of the oral fluid by the fading of the trap in solutions under the action of laser radiation before irradiation, after 30 and 60 min. The laser radiation parameters were set as follows: power 1 W, nanosecond pulsed radiation with a pulse duration of 400 ns and a frequency of 0.5, 1.0, 1.5 and 2.0 MHz in comparison with the continuous radiation mode.
 Results. It has been established that nanosecond laser radiation leads to the oxidation of a chemical singlet oxygen trap solubilized with sodium dodecyl sulfate (0.05 M SDS) detergent in the oral fluid and saliva flushing from the oral cavity. In pulsed nanosecond modes, laser radiation is more efficient than in continuous mode. With an increase in the repetition frequency, an increase in the effect by an average of 10% compared to a lower frequency was observed and the effect with a maximum frequency of 2.0 MHz was almost 50% higher than when using continuous radiation in all studies. A decrease in optical density at 414 nm was reliably observed in samples with oral fluid washing, the effect was 0.07 0.01 for 60 min of exposure. In the oral fluid, the effect with the same parameters was slightly lower and amounted to 0.05 0.03.
 Conclusions. The rate of fading of the trap in the saliva wash turned out to be 1.3 times faster than in water with detergent, which may indicate the activation of photoacceptors and their oversaturation with oxygen when using aqueous dilution of the oral fluid. The maximum effect was observed when using laser radiation with a pulse repetition rate of 2.0 MHz.

Mechanism in damage variation of nanosecond laser-induced damage of germanium sheets in vacuum

Laser-induced damage of germanium (Ge) sheets plays a key role to estimate the lifetime of optical components in the vacuum and space irradiation environment. However, the dependence between the degrees of laser-induced surface damage and nanosecond pulsed irradiation remains unclear for Ge sheet. Here, we investigate damage morphology and the growth characteristic of Ge sheets under different conditions and measure the laser-induced damage threshold (LIDT) in vacuum. Our results reveal that optical reflectivity of Ge in vacuum chamber falls 92% because of the defective sites on the damaged surface. The area, the depth and the size of the damage crater increase but the hillock height and the surrounding thermal diffuse area decrease along with the increase of vacuum degree. The thermal effect, the failure effect of plasma shock wave and the mechanical stress are analyzed to be the main mechanism in the laser damage. The combined experimental and theoretical work gives an insight into the change of surface damage and material failure behavior, hence broadens the potential applications of Ge sheets in areas of laser material manufacturing and laser processing.

Is orange carotenoid protein photoactivation a single-photon process?

In all published photoactivation mechanisms of orange carotenoid protein (OCP), absorption of a single photon by the orange dark state starts a cascade of red-shifted OCP ground-state intermediates that subsequently decay within hundreds of milliseconds, resulting in the formation of the final red form OCPR, which is the biologically active form that plays a key role in cyanobacteria photoprotection. A major challenge in deducing the photoactivation mechanism is to create a uniform description explaining both single-pulse excitation experiments, involving single-photon absorption, and continuous light irradiation experiments, where the red-shifted OCP intermediate species may undergo re-excitation. We thus investigated photoactivation of Synechocystis OCP using stationary irradiation light with a biologically relevant photon flux density coupled with nanosecond laser pulse excitation. The kinetics of photoactivation upon continuous and nanosecond pulse irradiation light show that the OCPR formation quantum yield increases with photon flux density; thus, a simple single-photon model cannot describe the data recorded for OCP in vitro. The results strongly suggest a consecutive absorption of two photons involving a red intermediate with ≈100 millisecond lifetime. This intermediate is required in the photoactivation mechanism and formation of the red active form OCPR.

Energy and spectral–temporal characteristics of a Fe:ZnSe laser on heavily doped single crystals

Energy and spectral–temporal characteristics of lasers on heavily doped single crystals Fe:ZnSe are studied. With the cavity formed by faces of the crystal at a bivalent iron concentration of 2.8 × 1019 cm−3, the slope and total laser efficiencies with respect to the absorbed energy were 53% and ≈ 42%, respectively. Laser spectra with the cavity free of air and elements capable of forming Fabry–Perot interferometers were recorded using a monochromator with an HPL-256-500 (HEIMANN Sensor) pyroelectric line photodetector. The spectra have a periodical structure with the period of about ≈ 4 cm−1. A similar periodical structure was observed in other cavity types with active elements differing in thickness, production technology, and even crystal material (Fe:ZnSe, Fe:ZnS). Presently, we have no adequate explanation for such a periodical structure. A simple method is suggested for obtaining nanosecond radiation pulses in the spectral range of 4–5 µm based on heavily doped Fe:ZnSe single crystals.

Bromine-isotope Selective Ionization Using Field-free Alignment of IBr Isotopologues with a Switched Nanosecond Laser Pulse

We demonstrate isotope selective ionization of I79Br and I81Br isotopologues using field-free alignment induced by a linearly-polarized nanosecond laser pulse with rapid turn off at the maximum. Following the “switched” nanosecond pulse irradiation, a 60-fs laser pulse ionizes one of the isotopologues preferentially. The ion yield ratio I(I81Br+)/I(I79Br+) varies in the range of 0.93–1.06, depending on time delay between the pulses. This is the first demonstration of laser isotope separation of heavy elements using field-free alignment and angular dependent ionization.

Acoustical monitoring of laser-matter interaction using nanosecond radiation pulses with periodically modulated intensity

Nanosecond laser ablation of metal target under the action of radiation pulses with periodically modulated intensity is investigated. Generated pressure pulses are detected by piezo-transducer (lithium niobate) on the back target side. Such approach permits to measure simultaneously recoil pressure behavior and calculate the irradiated surface displacement during laser action by comparison modulated parts of laser and acoustic signals. Nanosecond laser pulses contain 10–15 short peaks of 60 ps duration (1.08 μm wavelength) which provide fluence values up to 30 J cm−2 in the pulse. Plasma light emission is also registered with the help of photodiode. At the considered fluences surface displacement during the pulse turns out to be considerably smaller than theoretical estimation for free vacuum vaporization and measured experimental displacement which follows from the arrival time delay of another pressure signals generated with subsequent laser pulse directed to the same spot. Such behavior can be evidence that crater formation in the considered irradiation regime occurs after the pulse end.

Investigation of the laser-induced surface damage of KDP crystal by explosion simulation.

Under nanosecond pulse irradiation, laser-induced damage of Potassium Dihydrogen Phosphate (KDP) crystal is a multi-physical coupling process which mainly includes energy absorption by precursor defects, temperature and pressure rise in the absorption center, and subsequent micro-explosion event. Till now, related research work mainly focuses on modeling the energy absorption stage and determining the temperature or pressure in the absorption center, but knowledge about the explosion stage is rather limited. In this paper, laser-induced damage of KDP crystal has been investigated through explosion simulation. According to the laser damage test results and morphologies of the damage craters, typical precursor defects inducing KDP surface damage have been determined. Based on the knowledge, equivalent explosion simulation models of the laser damage process have been established to reproduce damage crater formation and shockwave propagation. Finally, laser damage experiments, combined with time resolved techniques, have been utilized to investigate the variation of damage crater size and shockwave speed with laser fluences. Simulation results given by single core explosion models agree well with the experimental results at fluences lower than 60 J/cm2, while a multicore explosion model is needed to reliably simulate damage crater formation at higher fluences.

Study of the photoluminescence properties of Eu2+-doped Ca(AlxGa1−x)2S4 solid solutions at high excitation intensity and low temperature

The investigation of photoluminescence (PL) properties of Ca(Al[Formula: see text]Ga[Formula: see text]S4:Eu[Formula: see text] solid solutions with [Formula: see text] = 0, 0.1, 0.2 and 0.3 synthesized for the first time was performed in wide temperature and excitation power density ranges. It is shown that PL intensity decreases by only 20–30% for different [Formula: see text] in the temperature range from 10 K to 300 K. The extreme stability of shape and position of the emission spectra was found in the range of excitation power density from [Formula: see text] W/cm2 to [Formula: see text] W/cm2 by nanosecond pulsed radiation. The reversible PL efficiency droop was only above 104 W/cm2 of excitation power density. The PL decay time constant was found to be of about 560 ns to 595 ns for [Formula: see text] ranging between 0.1 and 0.3 at room temperature.

Recording of Low-Power Nanosecond Radiation Pulses by a Detector Based on a Thin-Film Pyroelectric Structure

Results of an experimental study of a thin-film pyroelectric detector of radiation based on strontium barium niobate and used for detecting nanosecond radiation pulses are reported. The possibility of recording 30-ns radiation pulses with the sensitivity of 1 V/W (NEP = 8 · 10−7 W/Hz1/2) is demonstrated.

SiRNA release from gold nanoparticles by nanosecond pulsed laser irradiation and analysis of the involved temperature increase.

Nanosecond pulsed laser irradiation can trigger a release of nucleic acids from gold nanoparticles, but the involved nanoeffects are not fully understood yet. Here we investigate the release of coumarin labeled siRNA from 15 to 30 nm gold particles after nanosecond pulsed laser irradiation. Temperatures in the particle and near the surface were calculated for the different radiant exposures. Upon irradiation with laser pulses of 4 nanosecond duration release started for both particle sizes at a calculated temperature increase of approximately 500 K. Maximum coumarin release was observed for 15 nm particles after irradiation with radiant exposure of 80 mJ cm-2 and with 32 mJ cm-2 for 30 nm particles. This corresponds to a temperature increase of 815 and 900 K, respectively. Our results show that the molecular release by nanosecond pulsed irradiation is based on a different mechanism compared to continuous or femtosecond irradiation. Local temperatures are considerably higher and it is expected that bubble formation plays a crucial role in release and damage to cellular structures.

Generation of high-power Cherenkov superradiance pulses using 2D periodic slow-wave structures based on oversized cylindrical waveguides

We propose to stabilize the azimuthal structure of superradiance pulses using two-dimensional (2D) periodic Bragg structures that simultaneously play the role of a slow-wave system. Analysis performed in the framework of a quasi-optical approach is confirmed by the results of 3D particle-in-cell modeling that demonstrates the possibility of using the proposed system for generating multi-GW nanosecond radiation pulses in the millimeter waveband.

External focusing of nanosecond pulsed X-ray radiation

The feasibility of efficient focusing of high-power pulsed X-ray radiation generated by explosive electron emission from carbon nanoclusters is shown by direct experiments with the use of polycapillary X-ray optics. It is shown that the X-ray spot in the focus of the polycapillary lens can be reduced to 1/20 of its initial size.

Laser induced morphological and optical properties changes in Au doped aluminum oxide and silicon oxide thin films

Results on laser processing of thin oxide films containing gold are presented. The Au doped aluminum oxide and silicon oxide thin films are fabricated by pulsed laser deposition using targets composed by areas of gold and the oxide material. The as fabricates samples are processed by laser pulses with broad range of parameters – pulse duration, wavelength, fluence and pulse number. The changes of the morphology and optical properties after the laser irradiation are studied. It is found that laser irradiation with both nanosecond and femtosecond pulses may induce clear color change of the samples, which is accompanied by modification of the film structure. Nanosecond laser pulse treatment results in disintegration of the film induced by melting and surface tension forces. The process is accompanied by formation of nanoparticles at the edges of the surface modifications. At higher fluences nanosecond pulse irradiation leads to formation of wires composed of oxide material and gold nanoparticles. The femtosecond laser pulses induce a homogeneous decomposition of the film, as melt dynamics is not observed. The decomposition is however accompanied by color change of the irradiated area and clear dip in the transmission spectra. The dynamics of the film decomposition is discussed. The conducted study can be applied in fabrication of optical elements and in plasmonics.

Photothermal, photoconductive and nonlinear optical effects induced by nanosecond pulse irradiation in multi-wall carbon nanotubes

Abstract The influence of the optical absorption exhibited by multi-wall carbon nanotubes on their photothermal, photoconductive and nonlinear optical properties was evaluated. The experiments were performed by using a Nd:YAG laser system at 532 nm wavelength and 1 ns pulse duration. The observations were carried out in thin film samples conformed by carbon nanotubes prepared by an aerosol pyrolysis method; Raman spectroscopy studies confirmed their multi-wall nature. Theoretical and numerical calculations based on the heat equation allow us to predict the temporal response of the induced effects associated to the optical energy transference. A two-wave mixing method was employed to explore the third order nonlinear optical response exhibited by the sample. A dominant thermal process was identified as the main physical mechanism responsible for the optical Kerr effect. Potential applications for developing a monostable multivibrator exhibiting different time-resolved characteristics were analyzed.

Kinetic Monte Carlo simulations for transient thermal fields: Computational methodology and application to the submicrosecond laser processes in implanted silicon

Pulsed laser irradiation of damaged solids promotes ultrafast nonequilibrium kinetics, on the submicrosecond scale, leading to microscopic modifications of the material state. Reliable theoretical predictions of this evolution can be achieved only by simulating particle interactions in the presence of large and transient gradients of the thermal field. We propose a kinetic Monte Carlo (KMC) method for the simulation of damaged systems in the extremely far-from-equilibrium conditions caused by the laser irradiation. The reference systems are nonideal crystals containing point defect excesses, an order of magnitude larger than the equilibrium density, due to a preirradiation ion implantation process. The thermal and, eventual, melting problem is solved within the phase-field methodology, and the numerical solutions for the space- and time-dependent thermal field were then dynamically coupled to the KMC code. The formalism, implementation, and related tests of our computational code are discussed in detail. As an application example we analyze the evolution of the defect system caused by P ion implantation in Si under nanosecond pulsed irradiation. The simulation results suggest a significant annihilation of the implantation damage which can be well controlled by the laser fluence.

The formation of submicron structures on the surface of amorphous silicon films by nanosecond pulsed radiation of a laser line generator

The experimental results that were shown for the first time in this article concern the formation of nanostructures on the surface of amorphous silicon films deposited on the dielectric substrate under the influence of a laser beam swept in the form of a narrow line. Laser scanning was performed at a constant speed and at different power values with a radiation wavelength of 532 nm. The conditions of laser processing, when the aspect ratio of submicron structures on the surface of amorphous silicon film is the highest possible, were experimentally determined.

Kinetics of tunneling electron transfer between antimorphous defects in optical crystals with mobile cations

The experimental data on the transient optical absorption of wide-band-gap optical crystals of lithium borates Li2B4O7, LiB3O5, and Li6Gd(BO3)3 and potassium (KH2PO4 (KDP)) and ammonium (NH4H2PO4 (ADP)) dihydrogen phosphates in the visible and ultraviolet spectral regions are analyzed using the theory of diffusion-controlled tunneling recombination. A nanosecond pulsed radiation action on these crystals is shown to form defect pairs, such as polaron-type hole centers and electron centers based on interstitial cations. The relaxation kinetics of these centers over a wide time range of 10−8−10 s is described by a proposed model of tunneling electron transfer between antimorphous defects in the cation sublattice under the thermally stimulated mobility of recombination partners. The numerical values of the kinetic parameters are determined and the time dependences of the reaction rate constants are calculated for all crystals under study. As a result, the dynamics of change in the optical properties of these crystals under a pulsed radiation action can be simulated.

Output Enhancement of a THz Wave Based on a Surface-Emitted THz-Wave Parametric Oscillator

High-power nanosecond pulsed THz-wave radiation is achieved via a surface-emitted THz-wave parametric oscillator. One MgO:LiNbO3 crystal with large volume is used as the gain medium. THz-wave radiation from 1.084 THz to 2.654 THz is obtained. The maximum THz-wave average power is 5.8 μW at 1.93 THz when the pump energy is 84 mJ, corresponding to a energy conversion efficiency of 6.9 × 10−6. The polarization characteristics of THz wave are analyzed. During the experiments the radiations of the first-order and the second-order Stokes wave are observed.

Mode-Locked CO Laser for Isotope Separation of Uranium Employing Condensation Repression

In the present work, we have suggested a technical solution of a CO laser facility for industrial separation of uranium used in the production of fuel for nuclear power plants. There has been used a method of laser isotope separation of uranium, employing condensation repression in a free jet. The laser operation with nanosecond pulse irradiation can provide acceptable efficiency in the separating unit and the high effective coefficient of the laser with the wavelength of 5.3 μm. Receiving a uniform RF discharge under medium pressure and high Mach numbers in the gas stream solves the problem of an electron beam and cryogenic cooler of CO lasers. The laser active medium is being cooled while it is expanding in the nozzle; a low-current RF discharge is similar to a non-self-sustained discharge. In the present work, we have developed a calculation model of optimization and have defined the parameters of a mode-locked CO laser with an RF discharge in the supersonic stream. The CO laser average power of 3 kW is sufficient for efficient industrial isotope separation of uranium at one facility.

Theoretical and experimental study of laser induced damage on GaAs by nanosecond pulsed irradiation

The surface damage experiments of gallium arsenide (GaAs) single crystal irradiated by 1.06 and 0.53 μm nanosecond irradiations are carried out with fundamental and frequency-doubled Nd:YAG laser, respectively. The surface damage thresholds for both wavelengths are experimentally determined and the damaged morphologies and elementary component are analyzed with electron probe microanalyzer (EPM). It is found that the components of Ga and As almost keep constant in our experiments when the irradiated fluence is just around the surface damage threshold and no oxygen is found at all. The theoretical calculations on temperature rise for both wavelengths are carried out using the purely thermal model. It is shown that for irradiation with photon energy above the corresponding band gap the theoretical calculation is in good agreement with the experimental results; however, for that with photon energy just below the band gap, the experimental results cannot be effectively explained by the purely thermal heating mechanism. Combining with the experiment of multi-shot damage from references we finally conclude that the damage by laser irradiation with photon energy below the band gap should be explained by the micro-defect accumulation and consequently enhanced absorption heating mechanism.