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A full-dimensional ab initio potential energy surface for the H2–HF van der Waals complex was constructed by employing the coupled-cluster singles and doubles with noniterative inclusion of connected triples with augmented correlation-consistent polarised valence quadruple-zeta basis set plus bond functions. Using the improved coupled-states approximation including the nearest neighbor Coriolis couplings, we calculated the state-to-state scattering dynamics for pure rotational and ro-vibrational energy transfer processes. For pure rotational energy transfer, our results showed a different dynamical behavior for para-H2 and ortho-H2 in collision with hydrogen fluoride (HF), which is consistent with the previous study. Interestingly, some strong resonant peaks were presented in the cross sections for ro-vibrational energy transfer. In addition, the calculated vibrational-resolved rate constant is in agreement with the experimental results reported by Bott et al. These dynamics data can be further applied to the numerical simulation of HF chemical lasers. [ABSTRACT FROM AUTHOR]

In this work, by utilizing ionic liquid as the gain medium solvent, which is a new category of materials, we demonstrated a droplet-based dye laser system in a co-flowing microfluidic device. We characterized the droplet laser system and achieved a lasing threshold of 40.1 μJ/mm2. Owning to the unique properties of ionic liquids, such as negligible vapor pressure and good thermal and chemical stability, they offer great potentials for the development of on-chip light sources, tunable optofluidic devices, and sensitive biochemical analysis. [ABSTRACT FROM AUTHOR]

In recent times, the use of Chemical Warfare (CW) agents against civilian and military by terrorists and rogue countries are recurrent. The examples of such attacks are available in open literature. They are highly dangerous due to their acute toxicity nature. They tend to stimulate and paralyze nerve system of the body and cause other toxic side effects. Once these toxic chemicals are released into the atmosphere, timely detection and identification of the same at standoff distances will help the defensive forces to take proper counter measures. Detection techniques such as ion mobility spectrometry, infrared spectrometry, Raman spectrometry, FTIR, LIDAR, etc. have been used widely. Among all these techniques, Raman spectroscopy techniques and LIDAR (LIght Detection and Ranging) is the only active remote detection method that can detect and discriminate the chemical agents at standoff distances. Infrared DIAL (Differential Absorption Lidar) is a versatile technique for remote detection of various chemicals. DIAL technique can provide spatially resolved measurements of these agents with sufficient sensitivity (at few ppm levels) at ranges of several kilometers by exploiting the concept such as scattering and absorption from the atmosphere. The main objective of this review paper is to bring out the details of highly potential chemical warfare agents, their properties and laser based remote detection sensors. LIDAR technique is emphasized in more detail because of their long range detection capability, sensitivity and selectivity. An overview of existing R&D based and commercial systems is also discussed. [ABSTRACT FROM AUTHOR]

We have developed highly interleaved zigzag-shaped electrodes for collecting charge on the readout plane of various micropattern gaseous detectors (MPGDs), including gas electron multiplier (GEM) and micromega detectors. An optimized zigzag pad (or strip) anode can greatly enhance charge sharing among neighboring pads compared to traditional straight strip or rectangular pad designs and as a result can deliver excellent position resolution with minimal channel count, while exhibiting a virtually uniform response across the detector. We have systematically studied the effects of varying the parameters that define the zigzag geometry using simulations and have measured several printed circuit boards (PCBs) comprising a range of zigzag designs. Recently, we have employed laser ablation to generate zigzag patterns with pad-to-pad gaps smaller than 1 mil (or 25 μm). Reducing the gap well below the 3-mil limit imposed by traditional chemical etching has allowed the production of zigzag electrodes with unprecedentedly small feature sizes. In turn, laser-etched zigzag PCBs were shown to exhibit markedly improved performance over earlier generation PCBs, with position resolutions below 50 $\mu \text{m}$ for a 2-mm pitch. This article will explore in detail the dependence of the position resolution on the structural parameters of a zigzag-shaped anode, specifically for the case of a quadruple GEM detector. [ABSTRACT FROM AUTHOR]

The results of three-dimensional computational fluid dynamics model calculations are compared to available experimental results [V. D. Nikolaev et al., IEEE J. Quantum Electron. 38, 421 (2002)]. It is shown that the model is applicable to high pressure, ejector type chemical oxygen-iodine laser (COIL), reasonably reproducing the measured gain, temperature, static pressure, and gas velocity. A previous model, which included I2(A′3Π2u), I2(A3Π1u), and O2(a1Δg,v) as significant intermediates in the dissociation of I2 [K. Waichman et al., J. Appl. Phys. 102, 013108 (2007)], reproduced the measured gain and temperature of a low pressure supersonic COIL. The previous model is complemented here by adding the effects of turbulence, which play an important role in high pressure COILs. [ABSTRACT FROM AUTHOR]

The mechanism by which I2(B3Π0) is excited in the chemical oxygen-iodine laser was studied by means of emission spectroscopy. Using the intensity of the O2(b1Σ,υ′=0)→O2(X3Σ,υ″=0) band as a reference, I2(B3Π0) relative number densities were assessed by measuring the I2(B3Π0,υ′)→I2(X1Σ,υ″) emission intensities. Vibrationally excited singlet oxygen molecules O2(a1Δ,υ′=1) were detected using infrared emission spectroscopy. The measured relative density of O2(a1Δ,υ′=1) for the conditions of a typical oxygen-iodine laser medium amounted to ∼15% of the total O2(a1Δ) content. Mechanisms for I2(B3Π0) formation were proposed for both the I2 dissociation zone and the region downstream of the dissociation zone. Both pumping mechanisms involved electronically excited molecular iodine I2(A′3Π2u, A3Π1u) as an intermediate. It is proposed that in the dissociation zone the molecular iodine A′3Π2u and A3Π1u states are populated in collisions with vibrationally excited singlet oxygen molecules O2(a1Δ,υ′), whereas in the downstream region of the dissociation zone those intermediate states are populated by the atomic iodine recombination process. I2(B3Π0) is subsequently formed in collisions of I2(A′3Π2u, A3Π1u) with singlet oxygen. We also demonstrated that I2(B3Π0) does not participate measurably in the I2 dissociation process, and that energy transfer from O2(b1Σ) does not excite I2(B3Π0) to a significant degree. [ABSTRACT FROM AUTHOR]

Chemical oxygen-iodine lasers (COILs) oscillate on the 2P1/2→2P3/2 transition of atomic iodine at 1.315 μm by a series of excitation transfers from O2(1Δ). In electrically excited COILs (eCOILs), the O2(1Δ) is produced in a flowing plasma, typically He/O2, at a few to tens of Torr. Many system issues motivate operating eCOILs at higher pressures to obtain larger absolute densities of O2(1Δ) for a given yield and to provide higher back pressure for expansion. In this paper, we discuss results from a computational investigation of O2(1Δ) production in flowing plasmas sustained at moderate pressures (≤50 Torr). Power deposition and flow rates were scaled such that in the absence of second order effects, yield should be constant and absolute O2(1Δ) production should scale linearly with pressure. We found in many cases that absolute O2(1Δ) production scaled sublinearly with pressure. Ozone is found to be one of the major quenchers of O2(1Δ) and its production increases with pressure. Gas heating also increases with increasing pressure due to exothermic three-body reactions. The gas heating reduces O3 production, increases O3 destruction and, for certain conditions, restores yields. With increasing pressure and increasing absolute densities of atomic oxygen and pooling reactions of O2(1Δ), quenching by these species also becomes important, though the influence of O-atom quenching can be controlled by managing the density of O atoms with additives. The yield of O2(1Δ) is also determined by discharge stability which becomes problematic at higher pressure. [ABSTRACT FROM AUTHOR]

The development of high-energy lasers requires optical windows capable of handling megajoule beam energies without compromising the system’s performance. Calcium fluoride (CaF2) has been identified as a prime candidate for windows operating at chemical laser wavelengths due to very low bulk absorption and exceptionally small thermal lensing coefficients; it is, however, vulnerable to structural failure owing to poor mechanical strength characteristics and a large thermal stress factor. It is, therefore, essential to properly assess the ultimate potential of this material, which we attempt to do here in the following manner: (a) We assemble reliable numbers for all pertinent properties of (111)-oriented CaF2 single crystals and polycrystalline isotropic aggregates (PIAs), such as fusion-cast CaF2, which requires addressing issues relating to the elastic properties, the stress-optic coefficients, and the flexural strength. (b) We provide correct analytical expressions for evaluating the impact of pressure- and beam-induced effects on wave-front phase distortions and mechanical failure modes, taking advantage of a previous investigation [J. Appl. Phys. 98, 043103 (2005)]. (c) We perform detailed calculations on “model” windows made of either (111)CaF2 or (PIA)CaF2 that transmit optimally truncated Gaussian beams at wavelengths of 1.15 and 3.39 μm, for run times such that lateral heat conduction and surface cooling can be ignored. Our main conlusions are as follows: (a) With CaF2 windows thermal lensing, as measured in terms of the Strehl ratio and on assuming coating absorptances of no more than 3×10-5, is of no consequence in the sense that catastrophic failure may occur at fluence levels way below the threshold for optical distortion. (b) Evidence of a poor Weibull shape factor (m≃3.5) degrades the design safety margins, which requires operating at peak intensities of no more than 100 kW/cm2 to achieve optimum on-target fluences. (c) Regarding the issue of (111)CaF2 vs (PIA)CaF2, we note that fusion-cast material outperforms single crystals based on the figure of merit for distortion, as well as fracture and yield strengths, but contrary to (111)-oriented material, it exhibits birefringence that may rule out its use if depolarization is of concern. [ABSTRACT FROM AUTHOR]

In chemical oxygen iodine lasers (COILs), oscillation at 1.315 μm in atomic iodine (2P1/2→2P3/2) is produced by collisional excitation transfer of O2(1Δ) to I2 and I. Plasma production of O2(1Δ) in electrical COILs (eCOILs) eliminates liquid phase generators. For the flowing plasmas used for eCOILs (He/O2, a few to tens of torr), self-sustaining electron temperatures, Te, are 2–3 eV whereas excitation of O2(1Δ) optimizes with Te=1–1.5 eV. One method to increase O2(1Δ) production is by lowering the average value of Te using spiker-sustainer (SS) excitation where a high power pulse (spiker) is followed by a lower power period (sustainer). Excess ionization produced by the spiker enables the sustainer to operate with a lower Te. Previous investigations suggested that SS techniques can significantly raise yields of O2(1Δ). In this paper, we report on the results from a two-dimensional computational investigation of radio frequency (rf) excited flowing He/O2 plasmas with emphasis on SS excitation. We found that the efficiency of SS methods generally increase with increasing frequency by producing a higher electron density, lower Te, and, as a consequence, a more efficient production of O2(1Δ). [ABSTRACT FROM AUTHOR]

Chemical oxygen-iodine lasers (COILs) have promising applications due to their high efficiency and ease of scaling to multikilowatt powers. Recent research has focused on pumping the iodine with O2(1Δ) produced by electric discharges. In a previous work, a global model was used to develop reaction mechanisms and determine the specific energy deposition (eV/O2) required to obtain high O2(1Δ) yields for electric discharge COILs. Experiments have recently achieved positive laser gain and oscillation with these energy depositions and have highlighted the importance of axial expansion of the plasma in optimizing excitation of the O2(1Δ). In this work, the consequences of axial transport on O2(1Δ) yields have been computationally investigated in flowing He/O2 plasmas at a few Torrs using a one-dimensional plasma hydrodynamics and kinetics model. We show that the experimentally observed extension of the plasma glow upstream and downstream of the electrodes is due to electron diffusion and capacitive coupling of the radio-frequency power source. We also show that ≈50% higher O2(1Δ) yields can be achieved with a pulsed discharge combined with continuous-wave discharge. [ABSTRACT FROM AUTHOR]

A six-temperature kinetic model for a CO2-N2-He system is used to describe the dynamic processes of a mechanical Q-switched CO2 laser that is set up using a fast chopper. We put special emphasis on the effect of dynamical parameters on the laser intensity. It takes into account the effects of electrical excitation, energy transfer processes, thermal energy transport, as well as the dissociation of CO2 molecules and rotational relaxation of rotational levels. The results calculated are in satisfactory agreement with experimental data. [ABSTRACT FROM AUTHOR]

In conventional chemical oxygen-iodine lasers (COIL) the 1.315 μm transition in atomic iodine is pumped by a sequence of reactions of I2 and I with O2(1Δ) which is generated using liquid chemistry. Ongoing studies are investigating means to produce the O2(1Δ) precursor with an electric discharge (eCOIL) to enable a totally gas phase system. Due to the thermodynamic and power loading requirements, the plasma in eCOIL systems is sustained in a flow of a rare-gas diluent and the O2. In previous investigations, the scaling of production of O2(1Δ) was investigated using global-kinetics and one-dimensional (1D) models. It was found that the production of O2(1Δ) scaled linearly with energy deposition for moderate loadings (a few eV/O2 molecule). In this paper, these previous investigations are extended to two-dimensions using a plasma hydrodynamics model. The goal of this investigation is to determine if multidimensional considerations affect energy scalings for production of O2(1Δ). We found that O2(1Δ) production generally does scale linearly with energy loading, however, the saturation of O2(1Δ) production occurs at lower-energy loadings than predicted with global and 1D models. This trend is a result of the more accurately depicted and more localized energy deposition afforded by the two-dimensional model, and emphasizes the need for volumetrically uniform power deposition to optimize O2(1Δ) production. [ABSTRACT FROM AUTHOR]

We report on a detailed parametric study of the extremely efficient supersonic chemical oxygen-iodine laser recently developed in our laboratory [V. Rybalkin, A. Katz, B. D. Barmashenko, and S. Rosenwaks, Appl. Phys. Lett. 85, 5851 (2004)]. At the early stage of operation, 40.0% efficiency was measured for 1 s followed by a sustained 35.5% chemical efficiency for 20 s. The power and spatial distributions of the gain and temperature across the flow were measured for different supersonic nozzles with both staggered and nonstaggered iodine injection holes, different injection locations along the flow and nozzle throat heights. The effects of the partial pressure of O2 and the residence time of the flow in the generator, as well as the heating of the nozzle, are discussed and shown to be crucial in attaining this high efficiency. By carefully studying and optimizing the operation of the chemical generator, 0.73 yield of singlet oxygen was obtained for conditions corresponding to the highest efficiency. [ABSTRACT FROM AUTHOR]

We demonstrate molecular orientation by using phase-controlled two-color ω+2ω laser pulses with an intensity of 1.0×10[sup 12] W/cm[sup 2] and a pulse duration of 130 fs. The orientation of three iodine-containing molecules (IBr, CH[sub 3]I, and C[sub 3]H[sub 5]I) was monitored by the directional asymmetries of the photofragment angular distribution in dissociative ionization. In all three molecules, the directional asymmetry showed an oscillating behavior dependent on the relative phase difference between ω and 2ω pulses. The phase dependence of the directional asymmetry observed in iodine ions and counterpart ions were out of phase with each other. This result shows that a phase-controlled ω+2ω optical field discriminates between parallel and antiparallel configurations of aligned molecules that have a permanent dipole. This method performed well because (1) molecular orientation can be achieved by all-optical fields; (2) the direction of orientation is easily switched by changing the sign of the quantum interference; and (3) this method is free from any resonance constraint and thus can be applied to any molecule. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports that energy gain is detected theoretically in a pulsed chemical laser amplifier based on a photon-branched chain reaction initiating in a gaseous disperse medium composed of H[sub 2]-F[sub 2]-O[sub 2]-He and Al particles by focused external infrared radiation. Laser-chemical kinetics of the laser amplifier.

State-to-state rotational relaxation processes play a critical role in predicting rotational nonequilibrium, which can significantly affect total laser power and spectral distribution. In this paper, the state-to-state rotational relaxation rate coefficients for the pumping reaction of F + H2, the rotational energy transfer processes of HF(υ, j = 0–10) + HF(υ′, j′ = 0–10) and HF(υ, j = 0–10) + H2 are calculated. Subsequently, a detailed state-to-state chemical kinetic mechanism is constructed including 61 species and 124,482 elementary reactions for HF chemical lasers. All of these rotational relaxation rate coefficients have been expressed with Arrhenius-like formulas. A comparison of the Boltzmann distribution model with the detailed state-to-state chemical mechanism has been analysed and discussed. These results show that rotational nonequilibrium processes can significantly affect the distribution of ro-vibrational excited HF molecules. The rotational distributions of HF(υ = 0–2, j) are far from equilibrium distribution. Conversely, the distributions of HF(υ = 3, 4, j) seem to be a Boltzmann distribution. These results indicate that numerical models must include the rotational nonequilibrium processes and numerical models using a Boltzmann distribution for the rotational populations cannot predict performance of real HF chemical lasers. [ABSTRACT FROM AUTHOR]

Reports on the spectral optimization of a pulsed multiline HF chemical laser for efficient energy delivery through a low-loss fluoride glass optical fiber. Discussion on HF laser line selection methods; effect of carbon dioxide gas pressure on the total multiline output energy; Description of the process of energy delivery through the fluoride glass fiber.

Presents information on a study which investigated the characteristics of a high-pressure pulsed singlet oxygen generator for pulsed chemical lasers. Experimental procedure; Results and discussion; Conclusion.

Presents a numerical model for calculating the performance of a premixed pulsed supersonic hydrogen fluoride chemical laser. Integration of the laser kinetic equations and supersonic gas dynamics; Conditions for maximum gain and maximum laser energy for each of the input parameters; Information on the lasing zone length in the flow direction.

Present a study that theoretically investigated the output performance of a pulsed discharge initiated hydrogen/fluorine chain first vibrational overtone hydrogen fluoride chemical laser. Outline of a model to understand high efficiency overtone lasers; Results; Discussion.

Presents information on a study which investigated a novel computer model of a pulsed H[sub2]/SF[sub6] nonchain first vibrational overtone hydrofluorocarbon chemical laser to assess the overtone and fundamental laser performances. Demonstration of the first lasing of the vibrational overtone laser; Variation of the overtone laser energy with helium pressure; Description of the model.

Discusses the potential use of TII/Xe system as a continuous wave (cw), completely cyclic, self-contained atomic iodine laser. Pumping processes for the excited atomic iodine; Shortcomings of cw photolytically excited atomic iodine lasers; Factors that excited the TII dissociative levels in the rf discharge.

Presents a study which examined the quenching of NF singlet states in a hybrid chemical laser system. Experimental details; Results and discussion; Conclusion.

Focuses on four gain models for use in analyzing source-flow chemical laser resonators. Effect of using the gasdynamic calculation from the single-line model in a rotational nonequilibrium kinetics model; Details of an error introduced by decoupling the solution to the gasdynamic and laser kinetic equations; Impact of rotational nonequilibrium phenomena on lasing performance.

Presents a study that investigated the effects of fluorine donor additives and initiation level on hydrogen fluoride chemical lasers. Methodology; Analysis of the output characteristics of the laser; Measurement of the laser energy.

The laser emission spectrum of a flash initiated XeF2–D2 chemical laser indicated that translationally hot F atoms (31 kcal/mol) react with D2 to yield DF primarily in the v=2 state. Reaction of D+XeF2 was found to be too slow to contribute to the observed laser emission. [ABSTRACT FROM AUTHOR]

The rotational relaxation of HCl (v=1) by HCl is studied by infrared double resonance using two chemical lasers. State-to-state rate constants are derived from the measurements by comparison with a computer simulation based on two different scaling laws. The ECS theory based scaling law seems to provide a better fit to the experimental data than does the exponential gap law. With both scaling laws a correct description of the double resonance is obtained by including multiple rotational quantum transitions. [ABSTRACT FROM AUTHOR]

The chemical kinetics of supersonic hydrogen fluoride (HF) chemical lasers determines combustion characteristics and output power. However, the inherent complexity of chemical reactions and complex structure still challenge the numerical simulations involving a comprehensive chemical mechanism. Therefore, a high fidelity and low computational consuming model is important for design purpose. This paper presents a strategy to generate a reduced mechanism for HF chemical lasers. Based on a detailed HF chemical mechanism consisting of 16 species and 153 elementary reactions, a specific skeletal mechanism including 11 species and 58 elementary reactions is generated. Finally, we obtain a further reduction mechanism including 11 species and 39 elementary reactions by combining sensitivity analysis and rate of production analysis. The computational cost for simulation of supersonic HF chemical lasers with the reduced mechanism is less than that with the detailed model. The principal contribution of the work is to provide a low computational consuming model. [ABSTRACT FROM AUTHOR]

In this paper, the effect of air exposure and acetone cleaning on the secondary electron yield (SEY) of laser treated copper applied in accelerators for the inhibition of electron cloud was investigated and discussed. The SEY of laser treated copper samples after acetone cleaning and air exposure was measured. After 10–21 months air exposure, the maximum SEY increased by about 11%–20%. Furthermore, changes of carbon, copper, and oxygen chemistry states from sample surface after acetone and air exposure were studied by means of X-ray photoelectron spectroscopy. The XPS results show that the concentration of Cu from the surface of the samples with the thickness of 500 and $20~\mu \text{m}$ decreased by about 61%–70% after acetone cleaning and decreased by a further 36%–70% after 10–21 months air exposure. Moreover, the XPS measurement reflects the significant increase of the total percentages of C and O after acetone cleaning, and further increase after 10–21 months air exposure. The increase of SEY is explained in terms of the introduction of impurities, such as oxide and carbide. [ABSTRACT FROM AUTHOR]

Although the melting laser annealing can activate the heavily phosphorus-doped epitaxial Ge on silicon-on-insulator by chemical vapor deposition, the dopant segregation occurs after the rapid thermal process at 550 °C for 3 min even with SiO2 capping. However, the active dopant concentration can be recovered after the second laser annealing to melt Ge again due to higher P solubility in the liquid Ge than the solid Ge. The temperature distribution and the melt depth of epi-Ge is mainly determined by the laser fluence. Selective laser annealing is used to simultaneously reach low dopant concentration in the channel regions for good gate controllability, and high concentration in the source and drain regions with low parasitic resistance for the transistors. As a result, the low specific contact resistivity of $1.2\ \times \,\,10^{-8}\,\,\Omega $ cm2 using the Ni–Ge/n+Ge, the 21% current enhancement of the Ge + Si nFET as compared to the device without the selectively second laser annealing and the Ni–Ge contact, and the similar subthreshold slope after the selectively second laser annealing are achieved. The Si channel underneath the Ge channel also contributes about 38% of the total current. [ABSTRACT FROM AUTHOR]

Al is doped into 4H-SiC by irradiating pulsed KrF excimer laser to 4H-SiC immersed in AlCl 3 aqueous solution. Impact on doping depth of the use of expanded laser-pulse width is investigated. Expanded laser pulse is produced by splitting and recombining the laser beam with mirrors. The laser pulse width was expanded from its original width of 55–100 ns, while the peak power of the expanded pulse is as half as that of the original pulse under the same laser fluence. Multiple shots of the expanded laser pulses increased the doping depth at the Al concentration of 1×10 16 /cm 3 to 100 nm from 30 nm of the single shot of the original short, high-peak power laser. The increased doping depth could be due to enhanced diffusion by extra vacancies generated by the repeated laser irradiations. Due to the smaller laser peak power, the expanded pulse laser can suppress damage generation under multiple laser shots and, as a result, leakage current of the pn junction diode is kept low. [ABSTRACT FROM AUTHOR]

Both femtosecond and dual-wavelength picosecond operations of Nd,La:SrF2 disordered crystal laser have been demonstrated for the first time. In femtosecond operation, the laser generated mode-locked pulses with pulse duration of 156 fs, which is an average power of 90 mW, and a repetition rate of 108 MHz at the central wavelength of 1057 nm. In dual-wavelength picosecond operation, the laser generated synchronously mode-locked pulses with an average power of 500 mW and pulse duration of 9.9 ps. The mode-locked spectrum clearly shows two peaks at 1050.8 and 1059.0 nm, respectively. A periodic beat frequency of 2.2 THz is observed from the intensity autocorrelation trace, indicating the synchronous dual-wavelength mode-locking. Our experimental results show that Nd,La:SrF2 disordered crystal is an excellent laser material for femtosecond and dual-wavelength lasers near 1 μm wavelength. [ABSTRACT FROM PUBLISHER]

A novel resonant standoff quantum cascade laser (QCL) spectroscopy-based technique has been demonstrated for the detection of hazardous molecules (chemicals and explosives) on adsorbed surfaces, such as plastics and cloths, vapors, and in aerosols form in open air. Laser photoacoustic spectra of various trace molecules in the midinfrared spectral band 7– 9~\mu \textm have been recorded. Cylindrical tube coupled with microphone detector has been developed for the detection in trace amounts. The cylindrical tube has been developed for a compatible microphone detector working at resonant frequency of 40 kHz. The devised QCL-based acoustic detection setup has high selectivity and sensitivity. The present technique has been developed for screening of suspicious objects for security applications. It has the potential to be converted into a handy product. [ABSTRACT FROM PUBLISHER]

Directly pumped single-mode and multimode Ho3+-doped sol-gel silica microspheres lasing at $2.0~\mu \text{m}$ are observed, when an 1150-nm fiber Raman laser pump is used in a conventional microfiber-microsphere coupling method. Experimental results show single-mode output at $2~\mu \text{m}$ as well as the characteristic whispering-gallery-mode (WGM). By adjusting the taper contact position on the microsphere, we achieved switching between single-mode and multimode laser operations. [ABSTRACT FROM AUTHOR]

Features a study that analyzed the operational characteristics of the hydrogen-fluoride chain chemical lasers initiated by an intense electron beam in order to further improve the output performances. Optimization of the laser gas mixtures and the electron-beam-current density; Experimental results of the output characteristics; Comparison of theoretical and experimental results.

Presents a study that measured the delay time between the initiating pulse and the development of the laser emission pulse for various vibrational transitions in a supersonic Hartree-Fock chemical laser. Description of the apparatus; Analysis of the laser parameters; Results and discussion.

Presents information on a study which described the dependence of laser output power on the flow velocity at a cavity for a compact chemical oxygen-iodine laser. Description of chemical oxygen-iodine laser; Experimental apparatus; Results and discussion; Conclusions.

Develops a multikilojoule deuterium fluoride (DF) chemical lasers initiated by intense electron beams. Initiation modes of the DF lasers; Calculation of the initiation level; Means used to understand the temporal behavior of the DF laser pulse.

With laser-induced breakdown spectroscopy (LIBS), the elemental compositions of the room temperature-vulcanized silicone rubber and the high-temperature-vulcanized silicone rubber newly prepared samples were analyzed in this paper. The LIBS spectra showed that carbon (C), oxygen (O), aluminum (Al), silicon (Si), iron (Fe), and zinc (Zn) were contained in the samples, consistent with the energy dispersive X-ray spectroscopy (EDS) results. With scanning electron microscopy (SEM), the micromorphology and the depth of the ablation craters were observed. The craters’ sizes were only about 200\sim 400~\mu \textm , and there was nearly no difference between the hydrophobicity of the nonablated area and the ablated area, and the static contact angle of the craters was even larger than that of the nonablated area, meaning that the LIBS analysis was almost nondestructive. The depth of the ablation craters showed linearity relationship with the laser pulse number that would help a lot in the in situ analysis. Increasing the laser energy of the shot, the intensity of spectra lines of definite element and the electron number density would increase at the same time. The study result showed that the LIBS would be a promising element analysis technique of silicone rubber especially on line, and the composition of the composites could be clearly observed. [ABSTRACT FROM AUTHOR]

A chemical flow reactor is used to study the vibrational population distribution of CO produced by a reaction between carbon vapor generated in an arc discharge and molecular oxygen. The results demonstrate formation of highly vibrationally excited CO, up to vibrational level v = 14, at low temperatures, T = 400–450 K, with population inversion at v = 4–7, in a collision-dominated environment, 15–20 Torr. The average vibrational energy per CO molecule formed by the reaction is 0.6–1.2 eV/molecule, which corresponds to 10–20% of reaction enthalpy. The results show feasibility of development of a new CO chemical laser using carbon vapor and oxygen as reactants. [ABSTRACT FROM AUTHOR]

Multiphoton electron extraction spectroscopy (MEES) is an analytical method in which UV laser pulses are utilized for extracting electrons from solid surfaces in multiphoton processes under ambient conditions. Counting the emitted electrons as a function of laser wavelength results in detailed spectral features, which can be used for material identification. The method has been applied to detection of trace explosives on a variety of surfaces. Detection was possible on dusty swabs spiked with explosives and also in the standard dry-transfer contamination procedure. Plastic explosives could also be detected. The analytical limits of detection (LODs) are in the sub pmole range, which indicates that MEES is one of the most sensitive detection methods for solid surface under ambient conditions. Scanning the surface with the laser allows for its imaging, such that explosives (as well as other materials) can be located. The imaging mode is also useful in forensic applications, such as detection of explosives in human fingerprints. [ABSTRACT FROM AUTHOR]

Titanium–water complexes are produced by laser vaporization in a pulsed supersonic expansion, mass selected in a time-of-flight spectrometer, and studied with infrared laser photodissociation spectroscopy using argon complex predissociation. Density functional theory calculations provide structures and vibrational spectra for these ions. Spectra in the O–H stretching region indicate that the water is intact in these complexes, even though inserted structures are computed to be more stable. Although the ground state of Ti(H 2 O) + is established to be a quartet, that predicted and observed for Ti(H 2 O)Ar + is a doublet. Attachment of argon changes the electronic ground state of this system. [ABSTRACT FROM AUTHOR]

Nanostructured Al2O3–13 wt-% TiO2was prepared on AZ91D magnesium alloy surface by laser surface alloying to improve its corrosion resistance. The microstructure of the laser surface alloyed specimens before and after corrosion tests was characterised by scanning electron microscope and optical microscope (OM). The phase and element composition were investigated by X-ray diffractometer and energy-dispersive spectrometry. An electrochemical workstation was used to evaluate the corrosion behaviour of the specimens. Results showed that the laser surface alloyed layer was primarily composed of Mg and Mg17Al12. Al2O3and TiO2existed in the form of agglomerated particles. The corrosion resistance was improved after laser surface alloying. [ABSTRACT FROM AUTHOR]

Coating characteristics are highly dependent on substrate preparation and spray parameters. Hence, the surface must be adapted mechanically and physicochemically to favor coating-substrate adhesion. Conventional surface preparation methods such as grit blasting are limited by surface embrittlement and produce large plastic deformations throughout the surface, resulting in compressive stress and potential cracks. Among all such methods, laser patterning is suitable to prepare the surface of sensitive materials. No embedded grit particles can be observed, and high-quality coatings are obtained. Finally, laser surface patterning adapts the impacted surface, creating large anchoring area. Optimized surface topographies can then be elaborated according to the material as well as the application. The objective of this study is to compare the adhesive bond strength between two surface preparation methods, namely grit blasting and laser surface patterning, for two material couples used in aerospace applications: 2017 aluminum alloy and AISI 304L stainless steel coated with NiAl and YSZ, respectively. Laser patterning significantly increases adherence values for similar contact area due to mixed-mode (cohesive and adhesive) failure. The coating is locked in the pattern. [ABSTRACT FROM AUTHOR]

Transparent ocular tissues, such as the cornea and crystalline lens, can be ablated or dissected using short-pulse lasers. In refractive and cataract surgeries, the cornea, lens, and lens capsule can be cut by producing dielectric breakdown in the focus of a near-infrared (IR) femtosecond laser, which results in explosive vaporization of the interstitial water, causing mechanical rupture of the surrounding tissue. Here, we compare the texture of edges of lens capsule cut by femtosecond lasers with IR and ultraviolet (UV) wavelengths and explore differences in interactions of these lasers with biological molecules. Scanning electron microscopy indicates that a 400-nm laser is capable of producing very smooth cut edges compared to 800 or 1030 nm at a similar focusing angle. Using gel electrophoresis and liquid chromatography/mass spectrometry, we observe laser-induced nonlinear breakdown of proteins and polypeptides by 400-nm femtosecond pulses above and below the dielectric breakdown threshold. On the other hand, 800-nm femtosecond lasers do not produce significant dissociation even above the threshold of dielectric breakdown. However, despite this additional interaction of UV femtosecond laser with proteins, we determine that efficient cutting requires plasma-mediated bubble formation and that remarkably smooth edges are the result of reduced thresholds and smaller focal volume. [ABSTRACT FROM AUTHOR]

The effect of the (CFCO)O (trifluoroacetanhydride) buffer additive on the operation of an iodine photodissociation laser is studied experimentally. Comparative experiments for determining the laser energy of the iodine laser with the replacement of the working substance with this buffer additive and without it and with widely used buffer gas SF (sulfur hexafluoride) are carried out. Optical inhomogeneities in the working volume, emerging during pumping of working mixtures based on i-CFI (perfluoroalkyl iodide) with buffer additives (CFCO)O and CF (perfluorohexane), are measured. The results of experiments are analyzed. [ABSTRACT FROM AUTHOR]

High-power lasers typically form a multidisciplinary technological area laced with innumerable challenges in its realization as a practical system. The prime amongst them are infrared gas laser sources, such as carbon dioxide gas dynamic laser, hydrogen fluoride, deuterium fluoride laser, and chemical oxygen iodine laser. Each of these laser systems is associated with a unique as well as complex active medium environment involving intense interaction between lasing and pumping species under specific gas dynamic conditions. The parameters viz., specie concentration of the lasing, pumping mediums and other by-products, medium homogeneity, individual constituent gas flow rate, pressure and temperature at critical locations, and cavity Mach number are very crucial in determining the output of the gas laser system. It is essential to determine these parameters nonintrusively, with necessary precision so as to optimize these lasers especially in case of large-scale systems. Thus, the focus of this paper is to review and discuss the existing applicable optical detection methodologies ranging from the more established methods, such as optical absorption/emission spectroscopy, to very contemporary, such as Raman spectroscopy, cavity ring down spectroscopy, laser-induced fluorescence/planer laser-induced fluorescence, and so on, which are relevant for the diagnostic needs of gas lasers. [ABSTRACT FROM PUBLISHER]

The surface functional layers of commercial detector-grade CdTe crystals are characterized after different surface treatments such as chemical polishing etching in bromine-containing solutions and laser annealing with nanosecond pulses of the second harmonic of a YAG:Nd laser. The effects of etching and laser irradiation with energy density near the melting threshold of CdTe on the optical properties of the CdTe crystal surface are studied using ellipsometry and photoluminescence (PL). The samples after storage in air are also investigated. The intrinsic emission band at 1.58 eV and broad dopant band peaked at 1.45 eV are observed in the PL spectra excited by a semiconductor laser with wavelength of 405 nm at 80 K. The low energy band is associated with carrier recombination at structural defects in the surface layer. The redistribution of the PL band intensities after chemical polishing is found and it is attributed to transformation of the point defect structure and defect formation in the surface region of CdTe. The laser treatment essentially changes the surface state and structure of the surface layer that can be used for effective modification of characteristics of the functional layers of CdTe crystals particularly band bending before formation of electrical contacts. [ABSTRACT FROM PUBLISHER]

The Prague Asterix Laser System (PALS) Research Infrastructure (RI) in Prague, one of only four kJ-class laser facilities in EU, has been offering its beam time to European researchers for already 14 years, since 2004 in the framework of the LASERLAB-Europe consortium. Till June 2014, the PALS RI has provided 4313 experimental days for a total of 41 projects with 303 international users from 42 different research institutions. Its principal experimental facility is a terawatt sub-ns iodine laser (1315 nm) with an optional plasma-based zinc XUV laser (21.2 nm), and an auxiliary Ti:Sapphire fs laser (1 J, 70 fs) exploited for femtosecond plasma probing and experiments with synchronised femtosecond and sub-nanosecond laser pulses at mean laser intensities of up to 30 PW/cm2. The lasers are equipped with several target facilities and rich sets of instruments for both active and passive plasma diagnostics. The PALS main research areas include development and applications of secondary laser sources of high-energy ions and both coherent and non-coherent high-intensity XUV radiation, laboratory astrophysical and inertial fusion-relevant studies. In this paper, the main results having been achieved at PALS in the framework of LASERLAB-EUROPE international access activities during the last four years are highlighted. [ABSTRACT FROM PUBLISHER]

The pressure matching performance of the constant area supersonic-supersonic ejector has been studied by varying the primary and secondary Mach numbers. The effect of the primary fluid injection configurations in ejector, namely peripheral and central, has been investigated as well. Schlieren pictures of flow structure in the former part of the mixing duct with different stagnation pressure ratio of the primary and secondary flows have been taken. Pressure ratios of the primary and secondary flows at the limiting condition have been obtained from the results of pressure and optical measurements. Additionally, a computational fluid dynamics analysis has been performed to clarify the physical meaning of the pressure matching performance diagram of the ejector. The obtained results show that the pressure matching performance of the constant area supersonic-supersonic ejector increases with the increase of the secondary Mach number, and the performance decreases slightly with the increase of the primary Mach number. The phenomenon of boundary layer separation induced by shock wave results in weaker pressure matching performance of the central ejector than that of the peripheral one. Furthermore, based on the observations of the experiment, a simplified analytical model has been proposed to predict the limiting pressure ratio, and the predicted values obtained by this model agree well with the experimental data. [ABSTRACT FROM AUTHOR]