Theoretical studies on microscopic and macroscopic nonuniformities in electric-discharge-excited XeCl lasers

The satbilit r of the pumping discharge for XeCI (Ne/Xe/HCI) lasers is investigated by using different one-dimensional models, considering both bulk discharge instabilities and filamentary ones. It is found that the bulk stability in a XeCl laser discharge can he improved, under certain conditions, due to the vihrational excitation of HCl molecules: this effect is studied by using different models for the HCl vihrational kinetics. It is established that the very short instability time found in experiments cannot he explained as a result of hulk instability of the discharge. On the other hand, a satisfactory comparison with experiments can he obtained by adding to the model a simplified microinstability which develops in the discharge.     

Xenon chloride ultraviolet B laser is more effective in treating psoriasis and in inducing T cell apoptosis than narrow-band ultraviolet B

Earlier we reported that a 308-nm xenon chloride (XeCl) UVB laser is highly effective for treating psoriasis. As ultraviolet B light seems to cause T cell apoptosis, in the present study we studied the ability of the XeCl laser to induce T-cell apoptosis in vitro, and then compared the apoptosis-inducing capacities of narrow-band UVB (NB-UVB) light and the XeCl laser. The role of laser impulse frequency and intensity in the therapeutical and apoptosis-inducing efficacy of XeCl laser was also investigated. Both XeCl laser and NB-UVB induced T cell apoptosis, but quantitative induction was greater with XeCl laser. Changes in the frequency and intensity of impulses of XeCl laser did not influence its therapeutic and T cell apoptosis-inducing efficacy. These results suggest that the more effective induction of T cell apoptosis can be responsible for the greater clinical efficacy of XeCl laser compared to NB-UVB. Additionally, the optical properties of the XeCl laser (a monochromatic, coherent, pulse-mode laser; easier precise dosimetry, there are no 'contaminating' wavelengths) can make this laser light an ideal tool for studies of the mode of action of UVB light.     

Photochemical reduction of uranyl ion in nitric acid medium using a XeCl excimer laser

This paper describes the results of photoreduction of uranyl (UO₂ ²⁺) ion to U⁴⁺ in 0.2M HNO₃ and ethanol using a 308 nm XeCl excimer laser. The effects of different concentrations of ethanol and the addition of sulfamic acid on the quantum yield for U⁴⁺ formation are discussed.     

Intranasal irradiation with the xenon chloride ultraviolet B laser improves allergic rhinitis

We earlier reported that the 308 nm xenon chloride (XeCl) ultraviolet B (UVB) laser is highly effective for the treatment of inflammatory skin diseases. Since UVB irradiation has been shown to exert both local and systemic immunosuppression, we investigated the clinical efficacy of UVB irradiation in allergic rhinitis. In an open study, groups of patients with severe allergic rhinitis received intranasal irradiation with a 308 nm XeCl UVB excimer laser for two weeks. In the low-dose group (n=10), treatment was given twice weekly, starting with 0.25x the individual minimal erythema dose (MED), whereas patients in the medium-dose group (n=8) were treated four times weekly, starting with 0.4x MED. In each group, the dosage was gradually increased. Evaluation was based on the symptom scores. The effect of the XeCl laser on the skin prick test reaction was also studied. In the low-dose group, seven patients completed the study, and there was no improvement in the nasal symptoms. In the medium-dose group, the XeCl UVB irradiation significantly inhibited the rhinorrhoea, the sneezing, the nasal obstruction and the total nasal score (p<0.05). The XeCl UVB excimer laser also inhibited the allergen-induced skin prick test in a dose-dependent manner. These results suggest that the XeCl UVB excimer laser might serve as a new therapeutic tool in the treatment of allergic rhinitis.     

Morphological Investigation of Poly[methyl(H)silane-co-diphenylsilane] Irradiated by XeCl Excimer Laser

The morphological properties of poly[methyl(H)silane-co-diphenylsilane] copolymer (PSH) under XeCl (308 nm) laser irradiation were investigated. For this purpose, PSH films were exposed to XeCl excimer laser, 308 nm, at various UV doses (122 and 366 mJ/cm²), with 11 and 33 mJ/pulse and 1 Hz pulse repetition rate. The morphology of the PSH film surface was investigated by the atomic force microscopy (AFM) technique. AFM identifies that the films of the copolymer form a wormlike morphology before irradiation and conical defects are created on the polymer surface and grow with the laser irradiation.     

LASER-LIGHT INDUCED CHROMOSOME ABERRATIONS IN CHINESE HAMSTER CELLS

Wild-type Chinese hamster cells CHO Kl and their radiosensitive mutant xrs5 were irradiated at 308 nm, using light pulses of a XeCl excimer laser with total energy fluences of 0.1 kj/m² to 4.08 kj/m². Chromosome-type and chromatid-type chromosome aberrations have been observed at pulse irradiances of 2.5 × 10⁷ W/m² and 1.7 × 10⁸ W/m², indicating that in mammalian cells DNA double-strand breaks occur already in this irradiance range. The results obtained with laser irradiation are compared with X-ray irradiation.     

Determination of the photochemical efficiency of o-quinodimethane ring closure in room-temperature solutions by using time-delayed, two-color photolysis technique

Photochemical efficiency of o-quinodimethane (3) ring closure at room temperature was determined by using a time-delayed, two-color photolysis technique. o-Quinodimethane (3) was generated by the photolysis of 1,2-bis[(phenylseleno)methyl]benzene (1) by a KrF (248 nm) laser pulse and thus-generated 3 was photolyzed by a subsequent XeCl (308 nm)/XeF (351 nm) laser pulse with varying delay time of 0 to 3 s. The time profile of 3 was monitored by the chemical analyses of benzocyclobutene (5) (a photochemical product of 3), which was formed by a one-photon process, and the spiro dimer of 3 (4) (a thermal product of 3) in the two-color photolysis experiments. The time profile of 3 followed a second-order decay kinetics. The photochemical efficiency was obtained by the analysis of the delay-time dependence of the product yields; those of the consumption of 3 and the conversion 3-->5 by a single pulse of the excimer laser were 81% and 5.7% for the XeCl laser, and 73% and 2.3% for the XeF laser. This difference was attributed to the different excited states involved in the photolysis. In contrast to the photolysis of 3 in argon or rigid organic matrixes, it was revealed that photochemical conversion 3-->5 was not the main path in the solutions, and intermolecular reactions predominated.     

Analysis of glass by UV laser ablation inductively coupled plasma atomic emission spectrometry. Part 1. Effects of the laser parameters on the amount of ablated material and the temporal behaviour of the signal for different types of laser

Two lasers working in the UV part of the spectrum have been used for the analysis of glass samples. An XeCl excimer laser (308 nm) and a Nd:YAG laser operating at the third harmonic (355 nm) and the fourth harmonic (266 nm) have been selected. The energy was 100 mJ and 5 mJ for the excimer laser and the Nd:YAG laser, respectively. Because of different spot sizes, the fluence was of the same magnitude for both lasers. Crater characterization indicated that the laser ablation efficiency was similar for the two lasers when normalized to the same energy. However, the XeCl was found to be more efficient when the results were normalized to irradiance unit. The amount of probed material and ablated material was measured, leading to an efficiency higher than 80%. The influence of the glass colour and the laser wavelength was evaluated. The XeCl laser provided the largest amount of material but was sensitive to the glass colour. This laser was mainly suitable for bulk analysis. In contrast, the Nd:YAG, particularly at 266 nm, was insensitive to the glass colour and was appropriate for localized analysis. Inductively coupled plasma atomic emission spectrometry was used for atomization and excitation of the ablated material. A good agreement was found between the temporal behaviour of the amount of ablated material and the analyte signal.     

Plasma chemistry in laser ablation processes

Based on the results of quantitative spectroscopic diagnostics (LIF in combination with time resolved emission spectroscopy) chemical dynamics in laser-produced plasmas of metallic (Ti, Al,), and graphite samples have been examined. The Nd-YAG (1064 nm, 10 ns, 100 mJ) and excimer XeCl (308 nm, 10 ns, 10 mJ) lasers were employed for ablation. The main attention was focused on the elucidation of a role of oxide and dimer formation in controlling spatio-temporal distributions of different species in the ablation plume. The results of the spatial and temporal analysis of a laser-produced plasma in air indicates the existence of diatomic oxides in the ablation plume both in the ground and excited states, which are formed from reactions between ablated metal atoms and oxygen. The efficiency of the oxidation reaction depends on the intensity and spot diameter of the ablation laser beam. The maximal concentration of TiO molecules are estimated to be of 1×10¹⁴ cm⁻³ at the time of 10 μs after the start of the ablation pulse. A comparison of spatial–temporal distributions of Ti atoms and excited TiO molecules allow us to find a correlation in their change, which proves that electronically excited Ti oxides are most probably formed from oxidation of atoms in the ground and low lying metastable states. The spectroscopic characterization of pulsed laser ablation carbon plasma has also been performed. The time–space distributions as well as the high vibrational temperature of C₂ molecules indicate that the dominant mechanism for production of C₂ is the atomic carbon recombination.     

Efficacy of different UV-emitting light sources in the induction of T-cell apoptosis

Ultraviolet B (UV-B) radiation is a modality widely used for the treatment of different skin diseases. One of the major mechanisms of UV-B immunosuppression in this treatment modality is thought to be an apoptosis-inducing effect on T cells infiltrating the skin. We examined the T-cell apoptosis-induction capacities of four different UV light sources, with and without UV filters. The xenon chloride (XeCl) laser proved to be the strongest apoptosis inducer. The use of a phtalic acid filter eliminated UV radiation almost completely below 300 nm, which resulted in a severe decrease in the apoptosis-inducing capacity of different UV-B sources. Using the results of the measurements with polychromatic UV light sources, the wavelength dependence of UV-B light for the induction of T-cell apoptosis was also determined. The regression line of the action spectrum demonstrated a continuous decrease from 290 to 311 nm. The apoptosis-inducing capacity of the XeCl laser was almost four times higher than the calculated value according to the action spectrum, which might be attributed to the high irradiance of the laser as compared with nonlaser light sources.     

DBD Surface Modification of Polymers in Relation to the Spatial Distribution of Reactive Oxygen Species

The homogeneity of a helium dielectric barrier discharge, working at atmospheric pressure and containing oxygen as contaminant, is assessed by mapping the spatial distribution of oxygen metastable atoms in relation to the uniformity of surface properties. Tunable diode laser absorption spectroscopy is used to monitor the time evolution of the absorption coefficient corresponding to the oxygen metastable atoms on the 3⁵S₂ level, as a function of the laser absorbing path, whereas bi-dimensional Abel transform is used to obtain local information on the space distribution of the metastable atoms in the discharge. The radial distribution of the surface properties is investigated using atomic force microscopy, contact angle measurement and X-ray photoelectron spectroscopy. The results show that the oxygen metastables density has complex space–time behavior, and the spatial distribution of the reactive species yields specific radial profile of the surface properties of a polymer film depending on the treatment time.     

XeCl excimer laser coronary angioplasty: a convergence of favourable factors

The results of recent studies on the application of an XeCl laser to coronary angioplasty are presented. Several points are examined: the quality of the cut in human post-mortem artery, the cutting rates and threshold fluences in different media, the risks of carcinogenesis and thrombosis, and the transmission of suitable fluences in optical fibres. Recent human in vivo procedures are reported.     

XeCl laser action at medium fluences on biological tissues: fluorescence study and simulation with a chemical solution

A rat heart, isolated and perfused, was irradiated with a XeCl excimer laser at 308 nm. The evolution of the fluorescence spectrum was measured. For an incident energy E greater than 4 kJ m-2 per pulse the fluorescence changed with time in a complex and spectrally non-uniform way. The proposed interpretation is that the radiation acts on the cellular respiratory chain. Buffered solutions of NADH, cytochrome c and FAD, which play a role in the respiratory chain, were irradiated in order to simulate the in vivo findings. The conclusion of this study is that XeCl radiation introduces a modification in the functioning of the respiratory chain: it accelerates electron transfer, but this quickly leads to an interruption of the respiratory chain.     

Study of laser ablation of brass materials using inductively coupled plasma atomic emission spectrometric detection

A XeCl laser and a Q-switched Nd:YAG laser operating at 1064, 532, 355 and 266 nm were used to ablate brass materials with varying concentrations of Zn and Cu. The ablated material was transported to an inductively coupled plasma for further atomization, excitation and ionization with an atomic emission spectrometric detection. A Zn enhancement was observed, which could be suppressed by using a Nd:YAG laser working at 266 nm with fluences higher than 400 J cm⁻² (equivalent to 80 GW cm⁻²). In contrast, a lack of linearity was observed for Cu as a function of the concentration, regardless of the wavelength and the fluence. The Cu problem seemed to occur during the ablation and was related to the structure of the brass material. Lack of linearity was also observed for Zn and other contained elements when samples from different origins were used.     

Water Vapor Enhancement of Rates of Peroxy Radical Reactions

Peroxy radicals can complex with water vapor. These complexes affect tropospheric chemistry. In this study, β‐HEP (hydroxyethyl peroxy radical) serves as a model system for investigating the effect of water vapor on the kinetics and product branching ratio of the self‐reaction of peroxy radicals. The self‐reaction rate coefficient was determined at 274–296 K with water vapor between 1.0 × 10¹⁵ and 2.5 × 10¹⁷ molecules cm^?3 at 200 Torr total pressure by slow‐flow laser flash photolysis coupled with UV time‐resolved spectroscopy and long‐path, wavelength modulated, diode‐laser spectroscopy. The overall self‐reaction rate constant expressed as the product of both a temperature‐dependent and water vapor–dependent term is , suggesting formation of a β‐HEP‐H₂O complex is responsible for the increase in the self‐reaction rate coefficient with increasing water concentration. Complex formation is supported by computational results identifying three local energy minima for the β‐HEP‐H₂O complex. As the troposphere continues to get warmer and wetter, more of the peroxy radicals present will be complexed with water. Investigating the effect of water vapor on kinetics of atmospherically relevant radicals and determining the effects of these altered kinetics on tropospheric ozone concentrations is thus important.     

FLUORESCENCE DECAY KINETICS and CHARACTERISTICS OF BIMOLECULAR EXCITON ANNIHILATION IN CHLOROPLASTS

Abstract— The decay profiles of the fluorescence of dark-adapted spinach chloroplasts (0^A°C) excited with single 30 ps 532 nm laser pulses of varying intensities were measured with a low-jitter streak camera system. By comparing the decay profiles of the fluorescence at low and high laser fluences, i.e. in the absence and presence, respectively, of dynamic bimolecular exciton-exciton annihilation effects, the duration of such dynamic annihilation events can be estimated. A simple model suggests that the influence of bimolecular annihilation events on the fluorescence decay kinetics should disappear within a time interval corresponding to the low intensity, unimolecular lifetime of the exciton population which is subject to exciton-exciton annihilation. The low intensity fluorescence decay profiles are characterized by three to four lifetimes (Reviewed by A. R. Holzwarth, Photochem. Photobiol. 43,707–725, 1986); it is shown here that only the shortest fluorescence components are subject to exciton annihilation, since the kinetics of the fluorescence decay are influenced by annihilations only within the initial 150–200 ps time interval after the excitation pulse. The amplitudes (but not the decay kinetics) of the longer-lived fluorescence components are decreased at high levels of laser pulse excitations, suggesting that these components are derived from the shorter-lived fluorescence decay components. The implications of these results are*discussed within the contexts of current models of the fluorescence in chloroplasts.     

Oxygen discharge and post-discharge kinetics experiments and modeling for the electric oxygen-iodine laser system

Laser oscillation at 1315 nm on the I(2P1/2)-->I(2P3/2) transition of atomic iodine has been obtained by a near resonant energy transfer from O2(a1Delta) produced using a low-pressure oxygen/helium/nitric oxide discharge. In the electric discharge oxygen-iodine laser (ElectricOIL) the discharge production of atomic oxygen, ozone, and other excited species adds levels of complexity to the singlet oxygen generator (SOG) kinetics which are not encountered in a classic purely chemical O2(a1Delta) generation system. The advanced model BLAZE-IV has been introduced to study the energy-transfer laser system dynamics and kinetics. Levels of singlet oxygen, oxygen atoms, and ozone are measured experimentally and compared with calculations. The new BLAZE-IV model is in reasonable agreement with O3, O atom, and gas temperature measurements but is under-predicting the increase in O2(a1Delta) concentration resulting from the presence of NO in the discharge and under-predicting the O2(b1Sigma) concentrations. A key conclusion is that the removal of oxygen atoms by NOX species leads to a significant increase in O2(a1Delta) concentrations downstream of the discharge in part via a recycling process; however, there are still some important processes related to the NOX discharge kinetics that are missing from the present modeling. Further, the removal of oxygen atoms dramatically inhibits the production of ozone in the downstream kinetics.     

Kinetic features of chromium(VI) reduction and phenol degradation in aqueous solution by treatment in atmospheric-pressure air direct-current discharge

The kinetics of the processes of simultaneous reduction of Cr(VI) and degradation of phenol during the treatment of their aqueous solutions with different initial concentrations using an atmosphericpressure air direct-current discharge have been studied. The solution served as the discharge cathode. It has been shown that the discharge treatment leads to a decrease in the concentration of both Cr(VI) and phenol. Phenol additives accelerate the Cr(VI) reduction process and make it irreversible. The phenol degradation and Cr(VI) reduction kinetics are described well (R² > 0.99) by the pseudo-first-order rate equation in phenol and Cr(VI) concentrations, respectively. The apparent rate constants of the processes have been determined, the energy efficiency of the processes has been evaluated, and possible mechanisms of the proceeding reactions have been discussed.