Excimer System Research Articles

ANTI-SYMMETRY AND CAVITATION TOPOLOGICAL DISRUPTIONS OF COMPLEX SPACE AND INERT MASS ON THE BASIS OF EXCIMER SYSTEMS OF QUANTUM GENERATION OF EXCHANGE INERTIAL RADIATION. MONOMER EQUILIBRIUM AND MATTER FORMATION

The proposed mechanism of formation of inert mass, electric charge and gravitational mass through cavitational topological ruptures of complex space. Stabilization of gaps is carried out through the quantum generation of exchange inertial radiation. On the basis of the relations of non-relativistic quantum mechanics, such radiation was separated into two components: zeron radiation from the zero energy level of the quantum oscillator and heaton radiation from higher levels populated as a result of thermal excitations. Different signs of energy and temperature in two subspaces of the complex space form an antisymmetric excimer system of exchange inertial radiation generation, while the decomposition of these systems into monomers leads to the formation of stable and quasi-stable forms of matter. The parameters of such forms in elementary and cosmic systems are calculated. Quantitative relations in gravitational systems, obtained by the universal use of the constant fine structure and the extended analogue of the Planck constant, are consistent with actual data, in particular, regarding the jet expansion of the Metagalaxy, non-stationary processes in the interior and in the shells of celestial bodies, the mechanisms of thermoregulation of the Earth’s climate and the generation of the geomagnetic field. Turbulent energy cascades in tribocontact and collider systems, manifested in the emission spectra of excimer structures in these systems, are analyzed. The components of the inert mass of leptons, mesons, and hadrons were calculated, and the stabilization of the group velocity of heaton radiation quanta in the basis of giant nuclear resonances was found. The processes of tunnel breakdown of the energy barrier of excimers, which lead to the formation of energy vortices and jets in natural systems of different levels of organization, are analyzed. The negative consequences of mixing excimer structures of the inertial field with monomeric structures are shown on the example of well-known disasters in nuclear power and hydropower. It is shown that the widely reproduced Lorentz-invariant forms of the fields and the limitations of Einstein’s theories of relativity on the rate of propagation of interactions are adequate only in isolated monomeric systems where primitive conservation laws apply. The results obtained in the work are completely consistent with the fundamental theological concept of Creatio ex nihilo.

Stability and spectral properties of the dication Ne.

The dication Ne and its stability properties are studied by ab initio methods. Assuming the Born-Oppenheimer approximation and employing multireference configuration interaction techniques, potential energy curves of its low-lying electronic spectrum have been computed and analyzed. In addition to identifying metastable electronic and vibrational states, possible electronic transitions and decay mechanisms are examined. Our results also shed new light on the role of the dication as an excimer system and the interpretation of experimentally observed continua in Ne2 ultraviolet emission spectra.

Population inversion in sodium D2 transition based on sodium-ethane excimer pairs

Sodium-ethane excimer pairs are studied and proved to be a great choice of excimer pumped sodium laser (XPNaL) gain media. The lifetime of the sodium D2 line is studied in a sodium-ethane excimer system excited by a 553 nm laser, and the observed phenomenon of lifetime lengthening is discussed. Amplified spontaneous emission (ASE) of the sodium D2 line is successfully obtained, and its time-resolved and spectroscopic characteristics are studied experimentally. According to the intensity of the ASE signal under different sodium vapor atom densities, the sodium D2 line gain feature of sodium-ethane excimer pairs excited by the 553 nm laser is concluded.

Corneal stromal ablation with femtosecond ultraviolet pulses in rabbits

To determine the effectiveness of femtosecond ultraviolet (UV) pulses in ablating corneal stroma in a rabbit model and to compare the healing response between eyes treated with femtosecond UV pulses and eyes treated with standard excimer photorefractive keratectomy. Laser Research Center, Vilnius University, Vilnius, Lithuania. Experimental study. Myopic photoablation using a femtosecond UV solid-state laser system was applied to corneas of pigmented rabbits. Experiments in 16 eyes were performed for optimization of the laser system parameters (fluence, spot size, pulse repetition rate) and calibration of ablation rate. In 7 rabbits, deep femtosecond UV ablation (∼130 μm) in 1 eye and shallow ablation (∼30 μm) in the contralateral eye were performed. Nine rabbits received an approximately 30 μm ablation with femtosecond UV pulses in 1 eye and with a conventional excimer system in the contralateral eye. Two eyes were used as controls. The ablation process and surface-temperature dynamics were monitored and recorded. Surface quality and haze development were evaluated. Rabbits were humanely killed 0 to 6 months after surgery, and eyes were enucleated for histological examination. Rabbit corneas ablated with femtosecond UV pulses or excimer laser radiation were similar in terms of the corneal wound-healing process, surface quality, and histology. The experiments indicate the feasibility of clinical application of femtosecond UV lasers for stromal ablation. The ability to switch between laser harmonics allows fast changeover from infrared to the UV mode, implying that a wide range of ophthalmic procedures can be performed using a single solid-state laser device. Ms. Gabryte and Mr. Danielius are paid employees of Light Conversion Ltd. Mr. Danielius is a shareholder of Light Conversion Ltd. No other author has a financial or proprietary interest in any material or method mentioned.

308 excimer system: A new approach for practice therapy in the management of itchy skin diseases

308 excimer system: A new approach for practice therapy in the management of itchy skin diseases

Topography-guided hyperopic and hyperopic astigmatism femtosecond laser-assisted LASIK: long-term experience with the 400 Hz eye-Q excimer platform

The purpose of this study was to evaluate the safety and efficacy of topography-guided ablation using the WaveLight 400 Hz excimer laser in laser-assisted in situ keratomileusis (LASIK) for hyperopia and/or hyperopic astigmatism. We prospectively evaluated 208 consecutive LASIK cases for hyperopia with or without astigmatism using the topography-guided platform of the 400 Hz Eye-Q excimer system. The mean preoperative sphere value was +3.04 ± 1.75 (range 0.75-7.25) diopters (D) and the mean cylinder value was -1.24 ± 1.41 (-4.75-0) D. Flaps were created either with Intralase FS60 (AMO, Irvine, CA) or FS200 (Alcon, Fort Worth, TX) femtosecond lasers. Parameters evaluated included age, preoperative and postoperative refractive error, uncorrected distance visual acuity, corrected distance visual acuity, flap diameter and thickness, topographic changes, higher order aberration changes, and low contrast sensitivity. These measurements were repeated postoperatively at regular intervals for at least 24 months. Two hundred and two eyes were available for follow-up at 24 months. Uncorrected distance visual acuity improved from 5.5/10 to 9.2/10. At 24 (8-37) months, 75.5% of the eyes were in the ±0.50 D range and 94.4% were in the ±1.00 D range of the refractive goal. Postoperatively, the mean sphere value was -0.39 ± 0.3 and the cylinder value was -0.35 ± 0.25. Topographic evidence showed that ablation was made in the visual axis and not in the center of the cornea, thus correlating with the angle kappa. No significant complications were encountered in this small group of patients. Hyperopic LASIK utilizing the topography-guided platform of the 400 Hz Eye-Q Allegretto excimer and a femtosecond laser flap appears to be safe and effective for correction of hyperopia and/or hyperopic astigmatism. The results are impressive for refractive error correction and stability and for improvement of both uncorrected and corrected distance visual acuity.

Efficacy of an aspheric treatment algorithm in decreasing induced spherical aberration after laser in situ keratomileusis

To determine the effectiveness of an aspheric laser in situ keratomileusis (LASIK) algorithm for myopia with and without astigmatism in minimizing postoperative induction of spherical aberration. Four sites in Asia. Patients with -1.00 to -10.00 diopters (D) of spherical myopia with -4.00 D or less of astigmatism were recruited. Patients randomly had bilateral Zyoptix aspheric algorithm (aspheric group) or bilateral conventional Zyoptix Tissue Saving algorithm (control group). A Technolas 217z100 excimer system was used for LASIK ablation. Visual effectiveness, safety, higher-order aberrations, and corneal asphericity (Q value) were evaluated postoperatively. The aspheric group comprised 86 eyes and the control group, 84 eyes. At 3 months, the high-contrast uncorrected distance visual acuity was 20/20 or better in 78% of eyes in the aspheric group and 83% of eyes in the control group. The control treatment induced 0.22 microm of spherical aberration, which was significantly higher than the 0.04 microm induced with the aspheric treatment (6.0 mm pupil) (P<.0001). The aspheric treatment induced significantly less vertical coma and trefoil (P = .02). Eyes in the aspheric group had significantly lower Q values (P<.0001). There was no statistically significant difference in the manifest refraction spherical equivalent between the 2 groups (P >.05). Although high- and low-contrast corrected distance visual acuity (CDVA) was similar between the groups, the aspheric group gained more lines of low-contrast CDVA. The aspheric algorithm was more effective than the conventional algorithm in reducing induced spherical aberration and maintaining corneal asphericity after myopic LASIK.

Chloride Selective Calix[4]arene Optical Sensor Combining Urea Functionality with Pyrene Excimer Transduction

A neutral 2-site chloride selective compound has been developed (3), based on a 1,3-alternate tetrasubstituted calix[4]arene providing a preorganized supramolecular scaffold. The resultant supramolecular cavity is among the first to combine urea functional groups bridged with single methylene spacers to pyrene moieties. It combines a naturally and synthetically proven H-bonding system with the elegant ratiometric fluorescent signaling properties of an intramolecular pyrene excimer system, triggered by conformational changes upon anion coordination. The excimer emission of 3 is quenched, with a simultaneous rise in the monomer emission solely by the chloride anion among a wide variety of anions tested. 3 has an association constant of 2.4 x 10(4) M(-1) with chloride. The suitability and advantages of ratiometric optical sensor compounds like 3 for use in practical sensor devices is discussed. 3 has an LOD of 8 x 10(-6) M with chloride in acetonitrile-chloroform (95:5 v/v). A dynamic fluorescence study revealed a response time of < 3 s. A recently developed and simple HPLC-based purification method complimented conventional organic work up methods to yield pure product.

Fluorescence Studies on Binary Aromatic Compounds by Utilizing the Intermolecular Quadruple Hydrogen Bonding

Abstract Quadruple intermolecular hydrogen bonding of ureidopyrimidinone derivatives can be utilized to construct novel fluorescent excimer or exciplex system.

Feasibility of constructing a 100 TW femtosecond electric-discharge excimer system

Numerical simulation is used to show that conversion of radiation from a femtosecond XeCl excimer system by stimulated Raman scattering can be used to generate pulses with unique characteristics: a duration shorter than the reciprocal of the gain bandwidth, a steep leading edge, and a high contrast. A basic four-channel system with consecutive addition of pulses involving stimulated Raman scattering is proposed. It is shown that the total output power can reach 120 TW.

Capabilities of an Argon Fluoride 193 nm Excimer Laser for Laser Ablation Inductively Coupled Plasma Mass Spectometry Microanalysis of Geological Materials

Recent developments in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) have demonstrated its potential for in situ microanalysis for major, minor and trace elements in solids, such as minerals. With the low backgrounds and high sensitivity of new ICP-MS instruments, limits of detection of 1–10 ng g -1 in a 40 µm ablation pit for many elements can be reached. Fractionation effects due to different ablation rates of various elements have prevented quantification without matrix-matched standards with 1064 nm Nd:YAG lasers. These effects have been reduced but not eliminated using shorter UV wavelengths ( e.g . a quadrupled Nd:YAG 266 nm). Excimer lasers with wavelengths below 200 nm are expected to reduce fractionation effects further, but they present a serious challenge to the design of optical systems, especially if high-resolution UV ablation needs to be combined with high quality visual observation, which is essential for the study of complex materials, such as geological samples. An LA system was developed using an homogenized UV laser beam (193 nm, Argon Fluoride excimer) with a common UV–visual objective on a modified petrographic microscope with reflected and transmitted light illumination, in combination with a Perkin-Elmer Elan 6000 ICP-MS instrument. The optical system allows imaging of both visible and UV laser light onto the sample surface at the same time. Laser operating parameters and their influence on the ablation process were investigated using NIST SRM 612/610. Fractionation effects due to differential ablation of various elements as a function of time can be reduced to interelement correlation coefficients of r =0.9 or better and have become insignificant within the precision of quadrupole ICP-MS using this new optical design. Energy densities and repetition rates need to be kept within limited ranges for accurate and reproducible determinations of trace elements such as Zn, U and Pb, which have previously presented strong fractionation problems. LA-ICP-MS determinations on natural hornblende, augite, and garnet, calibrated against NIST SRM 612 using any major element as an internal standard, agree well with independent literature data. These experiments with the Argon Fluoride 193 nm excimer system demonstrate a greatly reduced matrix dependence of the ablation process, which facilitates in situ analysis of unknown samples.

A 170 J electron beam pumped XeF(C→A) laser

A pulse output energy of 170 J has been achieved from an XeF(C/spl rarr/A) laser system, pumped by a pair of counterpropagating, three-meter-long electron beams. This represents a record for all types of pumping, for this excimer system. Energy was extracted from a volume of /spl sim/100 L, using a free-running stable oscillator. No evidence of laser oscillations on the competing XeF(B/spl rarr/X) transition was observed. Within the extraction volume the laser gas was pumped at a rate of 140 kW/cm/sup 3/ (time average value), for a period of 1.7 /spl mu/s. The optical cavity was folded, giving a gain length of 6 m. The optical pulse duration was 0.8 /spl mu/s (full width at half maximum), and the observed flux buildup time of /spl sim/1 /spl mu/s was consistent with modeling and a measurement of the net gain. The specific output energy was 1.7 J/L which is comparable to that achieved in previous, small scale experiments at somewhat higher pump rate. The results confirm the volumetric scalability of the electron beam pumped XeF(C/spl rarr/A) laser system to high output energy per pulse, and the feasibility of operating this system at a low electron beam pump rate which relaxes constraints on the design of the electron gun and pulse power subsystems in a high output energy device. Means for extending the laser pulse duration and increasing the output energy of the specific test device are discussed. An output energy of /spl sim/1000 J is projected for an optimized gas cell width, for full size resonator mirrors, and with injection. >

Generation of short high-power pulses in excimer lasers by fast pulseQ-switching

The possibility of generation of short high-power pulses by pulse electroopticQ-switching in a high-gain excimer system was investigated numerically. Two methods of short-pulse generation were considered. In the first the electroopticQ-switch is controlled by two half-wave voltage gates. The method normally enables pulses from several hundreds of picoseconds to a few nanoseconds duration to be obtained. In the second method the Q-switch is controlled by a train of voltage gates of amplitude equal to the double half-wave voltage. In this case, even at short times of laser pumping (≈ 50 ns), it is possible to generate high-power pulses of duration from tens to several hundreds of picoseconds. The influence of various system parameters on the generation process and the parameters of the generated pulses was analysed in detail.

On the possibility of generation of picosecond pulses in an excimer laser by fast periodic Q-switching

Abstract A method of generation of picosecond pulses using fast periodic Q -switching in a high-gain excimer system was proposed. The influence of the switching time τ s , the medium pumping rate and the cavity geometry on the parameters of generated pulses was numerically investigated. It was found that at the laser gain g 0 l ⩾5 and τ s ⩽1 ns it is possible to generate of high-energy pulses of duration of few tens of picoseconds at relatively short time (≈50 ns) of the laser pumping.

Observation of continuous KrCl excimer fluorescence in microwave discharges employing binary mixtures of Kr and Cl2

A novel apparatus was designed to couple 2.45-GHz microwave radiation into a gas discharge. Using this apparatus, continuous-wave 222-nm B → X fluorescence of the KrF excimer system was observed in a binary mixture of chlorine and krypton. The effects of gas composition and total pressure on the fluorescence intensity at a wavelength of 222 nm was investigated. Spectra over the wavelength region of 200–320 nm were recorded for various gas compositions near the optimum total pressures for excimer fluorescence. The 222-nm B → X KrCl excimer transition was apparent in all cases and had a full-width half-maximum (FWHM) of 3 nm. In addition, the 258-nm Cl2 excimer transition was also evident with a FWHM of 5 nm. Both the center frequencies and widths of these transitions were constant for the conditions tested.

Background-free determination of the duration of ultraviolet radiation pulses generated by a femtosecond excimer system

Background-free determination of the duration of femtosecond ultraviolet radiation pulses generated in an excimer system was performed for the first time. The method of noncollinear second harmonic generation on reflection from the surface of a nonlinear crystal was used. It was found that amplification of femtosecond pulses in an XeCl excimer amplifier did not exhibit coherent effects.

Excitation energy transport and reversible trapping in aromatic vinylpolymers: Transient long-time behavior of a dissociative monomer–excimer system. A deterministic kinetic treatment

A deterministic kinetic analysis has been presented in an attempt to model the δ-pulse dynamics of a monomer–excimer pair in presence of energy migration and detrapping. Because of the reversibility of the system and the formal treatment of excitation energy transport by means of a time-dependent rate function k(t), the linear first order equations of evolution are coupled and consist of nonautonomous coefficients. The formalism involves a linear, affine transform technique for decoupling the simultaneous rate equations. This procedure leads to nonlinear, but decoupled first-order Riccati equations which have been further transformed to yield a second-order differential equation with time-dependent coefficients. For k(t)=b+Ct−1/2, the present study develops approximate WKB solutions to the transient δ-pulse response behavior of the system under the condition of weak coupling. The limitation of this approach have been tested towards numerical computer results. The WKB solutions are well behaved at relatively long times and, thus, prove useful for providing the typical asymptotic behavior of a polychromophoric monomer–excimer system in which transport and trapping will proceed via a quasi-one-dimensional pathway. The physics of this treatment has been discussed on the basis of energy-dispersive hopping processes along the chromophor array of aromatic polymer with typical, diagonal disorder. The analytical solutions, however, might have more general significance, presumably, with respect to forthcoming, subnanosecond reconvolution procedures in the transient fluoresence analysis of dilute aromatic vinylpolymers.

IMPROVED ANALYSIS OF TIME‐RESOLVED SINGLE PHOTON COUNTING FLUORESCENCE DATA OF EXCIMER/EXCIPLEX SYSTEMS USING A DUAL ANALYSIS ITERATED RECONVOLUTION PROGRAM ON A DEDICATED LABORATORY MICROCOMPUTER

Abstract A novel iterative reconvolution program for the simultaneous analysis of two sets of time‐resolved single photon counting (TRSPC) fluorescence data is described. Each set of data may be fit to a function containing up to three exponential terms and any of the parameters may be constrained to both sets. This dual analysis approach offers great advantages for the study of a coupled photokinetic scheme such as an excimer or exciplex system, both in terms of the accuracy of the results and in the simplicity and speed of the analysis.

Photophysical studies of pyrene on oxide supports. The effect of surface modification on probe dispersion and mobility

The pyrene monomer—excimer system was studied, under oxygen-free conditions, on silica and silylated silica in the loading range 2–200 μmole pyrene/g oxide. An analysis of the non-exponential monomer fluorescence decays in terms of a statistical model for probe adsorption and diffusive excimer formation is reported.

Laser induced phonons: A probe of intermolecular interactions in molecular solids

A new type of density dependent spectroscopy is developed and applied to the study of acoustics phonons and excited state–phonon interactions in molecular crystals. It is shown that intermolecular separations in solids can be varied in a controlled manner along a selected crystalline direction and that the consequences of the molecular displacements can be observed optically in time-resolved transient grating, absorption, and fluorescence experiments. The technique involves the generation of specific acoustic waves (phonon modes of definite wave vector) by transient grating optical excitation of the sample. The resulting time-dependent density changes cause time-varying spectral shifts, the magnitude of which are dependent on the detailed nature of the anisotropic intermolecular interactions in the crystal, e.g., anisotropic van der Waals interactions in molecular crystals can be directly investigated. First a formalism is presented which permits the determination of the nature of the phonons produced (longitudinal, quasilongitudinal, or quasitransverse) by transient grating excitation in anisotropic crystals. Next, the effect of the transient grating generated phonons on experimental observables (absorption, fluorescence, and transient grating) due to anisotropic spectral shifts is obtained. Model calculations illustrate the results. Finally experimental data for the perylene pure crystal excimer system and the pentacene in p-terphenyl mixed system are presented. In the perylene system, the various types of phonons predicted by theory are observed and phonon dispersions are obtained for several crystal directions. In pentacene in p-terphenyl, the theoretically predicted phonon-induced spectral shifts are clearly observed.