Preionization and discharge stability study of long optical pulse duration UV-preionized XeCl lasers

This paper presents a complete study of the temporal and spatial characteristics of the preionization of a XeCl rare-gas halide laser. The detailed study was made possible using the technique of laser-induced preionization which utilizes the uv radiation from a KrF laser to preionize a second rare-gas halide laser. In addition to the preionization study, high spatial and temporal resolution framing camera photographs have been used to investigate the growth of discharge instabilities which can lead to the premature termination of the XeCl optical pulse. The roles played by HCl, Xe, the buffer gas as well as the discharge energy loading in the development of discharge instabilities have been determined experimentally.     

RF exciplex halogen source of UV radiation on an argon-xenon-chlorine mixture

An exciplex halogen source of UV radiation that is excited by an rf transverse discharge is studied experimentally. The active medium of the source is an Ar-Xe-Cl₂ mixture kept at a low pressure (100–1000 Pa), and its working spectral range is 220–450 nm. The radiation spectrum contains 235 nm XeCl(D-X), 257 nm Cl₂(D′-A′), 306 nm XeCl(B-X), 390 nm XeCl(C-A), and 430 nm XeCl(B-A) lines. The results of optimization of the UV power as a function of the pressure, Ar-Xe-Cl₂ mixture composition, and excitation power are reported.     

Dual excimer and CO2 laser etching studies of polyethylene terephthalate

Polyethylene terephthalate (PET) films preheated with a pulsed CO₂ laser have been ablatively etched with an XeCl laser. The observed reduction in ablation threshold, from 170 to 140 mJ cm^–2, is consistent with a thermal mechanism for XeCl laser ablation of PET. Transient changes in the UV absorption coefficient of PET caused by heating with pulsed CO₂ laser radiation have also been studied and a significant increase in absorption observed at 308 nm. Permanent changes in the ultraviolet absorption of PET following exposure to low fluence XeCl laser radiation are also reported.     

Excimer lasers and laser systems

The results of the experimental study of UV lasers and laser systems pumped by different methods are presented. Two lasers were pumped by electron beams from Marx generators. Three lasers were pumped by transverse discharge with UV preionization. An XeCl laser pumped by electric discharge using a generator with inductive energy storage and semiconducting opening switch is investigated. The highest laser radiation energies of 2000, 90, and 0.7 J have been obtained at 5=308, 249, and 222 nm, respectively. The amplification of the laser beam from the master oscillator under conditions of strong amplified spontaneous emission is considered. In particular, formation of the output from an amplifier in the wings of the XeCl laser band and in the case of a large-aperture XeCl amplifier are investigated. The output beam divergence in these experiments was measured to be ~10^-4 rad.     

Simulation of the UV lamp source based on the longitudinal repetitively pulsed discharge in the Xe-CsCl mixture

An original kinetic model is used to simulate the characteristics of the XeCl exciplex UV source based on the mixture of Xe and CsCl vapor that is excited using the longitudinal repetitively pulsed discharge. The dependences of the radiation power and excitation efficiency of the XeCl exciplex molecules on the xenon and CsCl concentrations and the excitation pulse repetition rate are obtained. The calculated results are compared with the experimental data. The reasons for the limitations of the output radiation powers of the working mixture are discussed.     

Electric-discharge UV radiation source based on a Xe-CsCl vapor-gas mixture

A source of spontaneous UV radiation (excilamp) with a maximum radiation intensity at a wavelength of 308 nm is created. The active medium of the excilamp consists of a mixture of Xe with a CsCl vapor, and this mixture is excited in a longitudinal pulsed-periodic discharge. The B → X transition in the XeCl* exciplex molecule most strongly contributes to the total UV radiation power of the excilamp. The spectral composition of the UV radiation, the time characteristics of the source, and the formation of exciplex molecules as a function of the main discharge excitation parameters are studied.     

放电泵浦的多波长激光器

采用高气压紫外预电离放电装置和更换激射气体的方法,在一台器件上获得10个体系:F原子,Ne原子,N₂分子,N₂⁺离子,XeF,XCl,XeBr,KrF,KrCl,ArF相干辐射,并给出了激光器件的有关参数和输出特性等。 关键词：     

Spectral investigation of photochemical properties of polypropylene microfiber

Using the fluorescence, IR, and electronic spectroscopy methods, we have investigated the spectral characteristics of the surface of a polypropylene microfiber before and after their UV irradiation. We have studied the degradation of naphthalene and phenol in water exposed to UV radiation in the presence of fibers. As a radiation source, we used a KrCl excilamp with a radiation wavelength of 222 nm. It has been revealed that, after irradiation, photooxidation of the fiber surface occurs. The degree of crystallinity of examined samples remains almost the same after their irradiation. We show that, as a result of the adsorption of naphthalene and phenol on the fiber surface, their concentration in aqueous solutions efficiently decreases. Maximally, the concentration of naphthalene decreased 21-fold and that of phenol decreased 4-fold. Under UV irradiation of the system toxicant + water + fiber by the KrCl excilamp, fluorescent photoproducts are formed in the system and are adsorbed on the fiber surface.     

Luminescent analysis of photoinduced detoxification of phenol in the presence of humic substances

We have studied the effect of two detoxifying factors on aqueous solutions of phenol: UV radiation from different sources, and humic substances. The phenol photoconversion processes were monitored by the fluorescent method; the toxicity of the phenol solutions was monitored using a bioluminescence test. It was shown that effective detoxification of an aqueous phenol solution occurs as a result of addition of humic substances; the most effective photoinduced detoxification was detected when using UV radiation from an exciplex lamp (λ_rad = 308 nm). Other UV irradiation sources and the combined action of UV irradiation and humic substances are characterized by a smaller detoxifying effect. In this case, irradiation using an exciplex lamp (λ_rad = 222 nm) increases the toxicity of the phenol solution both in the presence and in the absence of humic substances. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 741–745, November–December, 2006.     

Xe-KCl excilamp

A source of UV radiation based on the B → X transition in the XeCl exciplex molecule entering into a Xe-KCl vapor-gas mixture is created. The emission properties of the excilamp (power, spectral composition, and time characteristics) are studied. Optimal conditions for excitation of the excilamp by a high-voltage pulsed-periodic discharge are found. The mean output and the efficiency of the excilamp are one order of magnitude higher than those of a Xe-NaCl lamp. The parameters of both radiation sources are analyzed in terms of the pumping efficiency.     

High brightness operation of a XeCl laser with negative branch unstable resonators

Confocal and non-confocal negative branch unstable resonators with an intracavity spatial filter have been applied to a high-gain short-pulse UV preionized XeCl laser. The near- and far-field radiation characteristics have been investigated in both configurations. Laser beams of larger brightness have been obtained with non-confocal schemes. A maximum beam brightness of 1.3×10¹⁴ Wcm^–2Sr^–1 has been achieved.     

具有高光学质量共焦和非共焦自滤波非稳腔的激光束

具有腔内滤光器的共焦和非共焦负支非稳腔应用于高增益、短脉冲紫外予电离氯化氙激光器,在上述两种腔结构,研究了各种空间滤光器条件下的近场和远场辐射特性,获得了有规则强度空间剖面的高亮度激光束,特别是非共焦机构,最大束亮度达1.3×10~(14)瓦·厘米平方·立体角,并且观察到,这种腔结构对于失调的低灵敏度.     

A simple tunable short-pulse XeCl laser with high spectral brightness

A simple tunable short-pulse XeCl laser system with a compact Blumlein circuit is described. In this system, radiation from a XeCl amplifier in order to achieve a wide tunable range and high spectral brightness. The generated radiation is tunable over 307.6–308.6 nm and the maximum peak power is 3 MW. Output pulse duration is shorter than 0.8 ns FWHM with a bandwidth of about 4 pm.     

UV Radiation of Low Pressure XeCl* and KrCl* Glow Discharges

The positive column of low pressure DC glow discharges in Xe/Cl₂ and Kr/Cl₂ gas mixtures has been investigated with respect to its UV radiation power and radiative efficiency for a wide range of parameters (total gas pressure: 1–30 mbar, current 10–30 mA, partial pressure of Cl₂: 1–33%). Also the radial distribution of the particle number densities of XeCl* (B) and KrCl* (B) has been determined by absolutely calibrated emission spectroscopy. Optimum UV (190–350 nm) output and efficiency has been found in gas mixtures with a relative Cl₂ partial pressure of 2–3% and total gas pressure of 12–18 mbar. At these parameters, the UV radiation power per column length is greater than 40 Watt/m with a radiative efficiency of 15–18%. These discharges could be used for UV induced photochemical processes.     

Luminescence of XeCl* and XeBr* exciplex molecules initiated by a longitudinal pulsed discharge in a three-component mixture of Xe with CsCl and CsBr vapors

The excitation of simultaneous luminescence of XeCl* and XeBr* exciplex molecules in a longitudinal pulsed-periodic discharge has been studied. To generate exciplex molecules, a three-component mixture of xenon with cesium bromide and chloride vapors was used. Spectral, energetic, and pulse-temporal characteristics of the discharge have been investigated, and the dependences of the UV luminescence yield on the composition and excitation conditions of the mixture have been studied. The average specific power of the discharge UV radiation in the Xe-CsBr-CsCl mixture has been determined to be 0.25 W/cm³, which corresponds to the total efficiency value ～0.7%. Also, mechanisms by which exciplex molecules are formed in a low-pressure vapor-gas mixture of the inert gas with halogenides of alkali metals have been considered.     

Biomaterial immobilization on polyurethane films by XeCl excimer laser processing

The surface chemical modification of polyurethane (PU) films was performed by an UV laser-induced chemical reaction in a polysaccharide solution. This process may be applicable as hydrophilic packaging of implantable medical devices and in vivo sensors. When a PU film in contact with an aqueous alginic acid (AAC) solution was irradiated with a XeCl laser, the PU film turned hydrophilic. Contact angles of water on the film were reduced from 110° to 60°. Since light absorption of the AAC solution at 308 nm was negligibly small, reactive sites were generated solely on the PU surface. There, AAC could be immobilized by chemical bonds thus allowing for a nanometer-scaled grafting of this biomolecule. The mechanism was investigated by surface analyses with Fourier-transform infrared spectroscopy (FT-IR), dye staining, ultraviolet-visible (UV-VIS) spectroscopy, and scanning electron microscopy (SEM) techniques. A one-photon photochemical process could beidentified. Received: 30 June 2000 / Accepted: 4 July 2000 / Published online: 13 September 2000     

Efficient rotational Raman conversion of XeCl laser radiation in H2

2 is investigated with a XeCl laser. It is shown that energy conversion to rotational Stokes radiation can be efficiently obtained by properly choosing the focusing geometry of pump radiation and the pressure of the Raman medium even at moderate pulse energies. Energy conversion to the first rotational Stokes at 313.8 nm with efficiencies as high as 38% is obtained with a circularly polarised XeCl pump beam of 10-mJ energy focused in 30 bar of H₂. The spectral and optical characteristics of the pump and the rotational Stokes radiation are analysed. Received: 29 May 1996/Revised version: 7 March 1997     

Aryltriazene photopolymer thin films as sacrificial release layers for laser-assisted forward transfer systems: study of photoablative decomposition and transfer behavior

Thin films of a tailor-made photodecomposible aryltriazene polymer were applied in a modified laser-induced forward transfer (LIFT) process as sacrificial release layers. The photopolymer film acts as an intermediate energy-absorbing dynamic release layer (DRL) that decomposes efficiently into small volatile fragments upon UV laser irradiation. A fast-expanding pressure jet is generated which is used to propel an overlying transfer material from the source target onto a receiver. This DRL-assisted laser direct-write process allows the precise deposition of intact material pixels with micrometer resolution and by single laser pulses. Triazene-based photopolymer DRL donor systems were studied to derive optimum conditions for film thickness and laser fluences necessary for a defined transfer process at the emission wavelength of a XeCl excimer laser (308 nm). Photoablation, surface detachment, delamination and transfer behavior of aryltriazene polymer films with a thickness from 25 nm to ∼400 nm were investigated in order to improve the process control parameters for the fabrication of functional thin-film devices of microdeposited heat- and UV-sensitive materials.     

A Miniaturized XeCl Dielectric Barrier Discharge as a Source of Short Lived,Fast Decaying UV Radiation

A dielectric barrier discharge (DBD) of coaxial geometry has been examined as source of intensive, short‐lived UV radiation. A binary gas mixture consisting of 98% Xe + 2% Cl₂ and a ternary composition of 96% Ne + 6% Xe + 0.2% HCl were investigated in the pressure range between 10 and 750 mbar. The discharge was excited by unipolar high voltage square pulses with amplitudes of 3 to 7 kV at a repetition rate of 100 Hz. UV radiation intensity is increased by combining 5 square pulses with a period of 1 μs each in one train (burst). Radiation decay on three orders of magnitude within 10 μs was obtained for both gas mixtures in burst mode. Maximum energy of the light pulse was the same for both gas mixtures and estimated as 40 nJ. It is shown that the optimum gas pressure for highest radiation intensity depends not only on gas composition but also on applied voltage and number of pulses in the train. A variation of the spectral band shape of XeCl emission during the pulse is detected (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Degradation and protection of polyaniline from exposure to ultraviolet radiation

The effect of UV radiation on both pure and additive-containing polyaniline thin films is described. Experimental investigations included optical transmittance spectroscopy and electrical conductivity measurements. Exposure to UV radiation in the range of 380 to 400 nm was seen to increase film transmittance by 4% through photobleaching. Different gas ambients were employed for this experiment and progressively more photobleaching was observed for nitrogen, air and oxygen atmospheres. This effect arises due to the destruction of quinoid and benzenoid chromophores on the polymer backbone. Concomitantly, a decrease in film resistivity was also observed and this can be attributed to increased oxidative doping of the film material. The addition of controlled amounts of Tinuvin 213—an ultraviolet absorber (UVA) material—was seen to reduce the UV-induced degradation of polyaniline thin films by absorption of UV photons through regenerative intramolecular photolysis.