Spectroscopic studies of UV production from ARC sources in iodine laser gas mixtures

Time-integrated spectral measurements of the light from multiple arc sources in iodine laser gas mixtures (He:SF₆:i-C₃F₇I and Ar:SF₆:i-C₃F₇I) are described. Copious soft-UV output, fully sufficient as a pump source, is observed with no adverse decrease in UV production for i-C₃F₇I concentrations as high as 3% by volume. Conversion efficiencies of 3–4% for stored electrical energy into UV radiation within the iodide compound band were determined.     

Subject index

Lead iodide is known to dissociate under band gap illumination. We investigated the decomposition products from sintered samples by quadrupole mass spectrometry and found that neutral atomic and molecular iodine species desorb from the illuminated surface. The desorption rate was measured as a function of light intensity and surface temperature. Atomic iodine desorption seems to be thermally activated throughout the temperature range (300–500 K), while molecular iodine has that feature only up to 400 K. We performed measurements of the dark and photoconductivity of PbI₂ as functions of temperature and light intensity. Correlations of those results with the photolysis mass-spectrometric data indicate a possible model for the dissociation process. It suggests a diffusion-controlled mechanism of iodine desorption as well as of the dark conductivity, which seems to be ionic in that temperature range. The molecular iodine is apparently formed in surface sites, such as grain boundaries, which have a longer life-time for adsorbed iodine atoms as well as a dominant role in surface electronic conduction.     

The formation of a surface iodide on Ni{100} and adsorption of I2 at low temperatures

Iodine adsorption on clean Ni[100] has been investigated using low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). At temperatures below 340 K. a saturated surface of adsorbed iodine atoms in a c(2 × 2) structure is observed. Adsorption of iodine on clean Ni{100} at temperatures in exces of 370 K forms a structure identified as a single layer of the layered compound NiI₂ on the metal substrate. Solid iodine is shown to grow epitaxially on both the c(2 × 2) chemisorbed surface and the surface iodide at temperatures less than 185 K. Heating to 185 < T < 226 K leaves a physisorbed molecular iodine layer, while on returning to room temperature the original c(2 × 2) or iodide is restored.     

127)I2在633nm波段的超精细强谱线及稳频半导体激光器

报道了观察到的碘分子（¹²⁷I₂）在633nm波段的5组超精细强谱线,并对每组谱线的频率间距及相应振转能级的跃迁强度作出了计算,结果和实验吻合得很好．利用计算结果,对这5组谱线对应的振转能带作出了甄别．由于这些新谱线比用于氦氖激光器稳频的R（127）11.5跃迁强几百倍,因此利用这些新谱线作为半导体激光稳频的参考谱线,得到了功率为3mW的激光输出,这种半导体激光可成为新型光频标． 关键词：     

Multiphoton ionization of iodine atoms and CF<Subscript> 3</Subscript>I molecules by XeCl laser radiation

We report about effective ionization of iodine atoms and CF₃I molecules under the action of intense XeCl laser radiation (308 nm). The only ion fragment resulting from the irradiation of the CF₃I molecules is the I⁺ ion. We have studied the influence of the intensity, spectral composition, and polarization of the laser radiation used on the intensity of the ion signal and the shape of its time-of-flight peak. Based on the analysis of the results obtained, we have suggested the mechanism of this effect. The conclusion drawn is that the ionization of the iodine atoms by the ordinary XeCl laser with a nonselective cavity results from a three- (2 + 1)-photon REMPI process. This process is in turn due to the presence of accidental two-photon resonances between various spectral components of the laser radiation and the corresponding intermediate excited states of the iodine atom. The probability of ionization of the atoms from their ground state I(²P_3/2) by the radiation of the ordinary XeCl laser is more than two orders of magnitude higher than the probability of their ionization from the metastable state I^*(²P_1/2). The ionization of the CF₃I molecules by the XeCl laser radiation occurs as a result of a four-photon process involving the preliminary one-photon dissociation of these molecules and the subsequent (2 + 1)-photon REMPI of the resultant neutral iodine atoms.     

Iodine photodissociation laser SOFIA with MOPO-HF as?a?solid-state oscillator

The hybrid iodine photodissociation laser SOFIA has been constructed. The pulse feeding the amplifier chain is the idler wave of an optical parametric oscillator (OPO) tuned to the atomic iodine transition at 1315 nm. This solid-state oscillator enables ps-synchronization to other laser systems. A homemade automatic stabilization of the OPO idler wave as to wavelength and pointing ensures long-term stable operation of the whole system. The active medium of the SOFIA amplifiers is a mixture of C₃F₇I and He. The SOFIA pulses are frequency-tripled in two KD*P crystals and then serve as the driver in a two-stage optical parametric amplification scheme in which chirped broadband Ti:sapphire laser pulses are amplified (OPCPA).     

Influence of parameters of gas medium on the fluorescence of iodine molecules 129I2, 127I129I and 127I2 excited by semiconductor laser radiation

Calculated and experimental results of studies of the influence of vapor temperature of iodine molecules (¹²⁹I₂, ¹²⁷I¹²⁹I, and ¹²⁷I₂) and pressure of the analyzed medium on the intensity of fluorescence of the molecules excited by semiconductor laser radiation in the red spectrum region are reported. It is demonstrated that depending on the wavelength of laser radiation there exist different ranges of temperatures and pressure values at which the fluorescence intensities of each of the indicated iodine molecules reach their maximum values.     

Kinetics of I2 and HI photodissociation with implications in flame diagnostics

This paper investigates the application of iodine (I₂) tracer in reactive flows to image the concentration filed by using photodissociation spectroscopy (PDS). The PDS technique first uses a short laser pulse to completely photodissociate iodine-containing species into iodine atoms, and then uses a second laser pulse to image the iodine atoms. Due to the completeness and rapidity of the photodissociation (PD), the concentration of I atoms after PD represents that of the iodine element seeded into the flow, which forms a conserved scalar and can be used to image the concentration field. The feasibility of the PDS technique is evaluated in three steps. First, a multi-level kinetic model was developed to capture the major physics relevant to the PDS technique. Second, controlled experiments were conducted to validate the multi-level kinetic model. Third, the validated model was applied to evaluate the applicable range and accuracy of the PDS technique in representative hydrocarbon flames. The results suggest a simple approach to implement the PDS technique using I₂ seeding in flames, which can provide good accuracy across a wide range of mixture fractions and strain rates.     

Effect of composition on properties of reactive Al·B·I2 powders prepared by mechanical milling

Metal-based fuels producing halogen-containing combustion products are being developed to enable rapid inactivation of harmful aerosolized spores and bacteria. Ternary reactive materials containing aluminum, boron, and iodine were prepared by mechanical milling with systematically varied Al:B ratio. The aluminum mass fraction varied from 0% to 70%, and most materials included 20 wt% of iodine. Prepared powders were inspected by electron microscopy; particle size distributions were measured using low angle laser light scattering. Stability of materials was studied using thermo-gravimetry and differential scanning calorimetry. As-prepared as well as pre-heated and quenched samples were analyzed using x-ray diffraction. Iodine was released upon heating in several stages. Low-temperature iodine release was relatively small. It overlapped with decomposition of B(OH)₃ releasing water. The most significant amounts of iodine were released when the samples were heated to 400–500 °C, when AlB₂ formed. Both AlB₂ formation and iodine release were further accelerated by melting of aluminum. For the boron-rich samples, in which boron remained after all aluminum was used to form AlB₂, an additional, high-temperature iodine release stage was observed near 900 °C. The results show that both boron and aluminum are capable of stabilizing substantial quantities of iodine in the metal matrix. The iodine is released at temperatures much greater than its boiling point. The mechanism by which iodine is retained in boron and aluminum remains unclear.     

n2-measurements at 1.32 μm of some organic compounds usable as solvents in a saturable absorber for an atomic iodine laser

We have measured the nonlinear index of refraction n₂ of 12 organic compounds by means of a time integrating interferometric technique using pulses of about 0.7 ns duration from an atomic iodine laser working at 1.32 μm. The accuracy of the n₂-values obtained is ± 20%. The results may help to facilitate the proper choice of a solvent for a dye usable as a saturable absorber for an atomic iodine laser.     

Time structure of iodine laser pulse in the free running mode of operation

Time structure of iodine laser pulse in the free running mode of operation was studied using the power amplifier of laser system PERUN as the laser oscillator. Two characteristic shapes of laser pulse correspond to different regimes of laser operation, the existence of which is ascribed to the critical concentration of I₂ molecules. Simultaneously an additional chemical pumping was proved at least in the initial phase of photodissociation and in a late-time lasing after the end of flashlamps pumping light.     

Production of fullerenes by a near infrared laser

Preparation of macroscopic amount of C₆₀ clusters (fullerenes) by the iodine laser is reported.     

Characteristics of 20 year old iodine cell and compact iodine stabilized laser

Spectral quality and reliability of four kinds of¹²⁷ I ₂ cells for an wavelengtn standard were investigated. A 20 year old 10 cm long sealed off iodine cell has shown its long life and had sufficient absorption characteristics comparable to the newly made three cells in regard to spectral line width and signal-to-noise ratio of the absorption signal. A dispersion of absolute frequencies of the three cells including the 20 year old cell is in a range of 35 kHz, which is equivalent to a frequency reproducibility of 7.4X10^-11. A compact iodine stabilized 633 nm He-Ne laser with a 23 cm long resonator and 4 cm iodine cell has been developed. Its frequency stability has been estimated to be 9X10^-13 by the Allan deviation at integration time of 4000 s. The laser supplies 14 wavelength standards being locked at iodine absorption lines from a ton.     

Description and application of an intense and short diagnostic source between 1000 and 1600 nm

We describe a possibility to obtain by a mode-locked YAG neodynium laser and a simple Raman conversion into O₂ and NO gas, a very fast and intense source for diagnosis centered on convenient wavelength (1060-1300-1600 nm) which allows to characterize devices used for optical fiber systems or for iodine laser.     

Development of the Chemical Oxygen-Iodine Laser (COIL) with chemical generation of atomic iodine

This article addresses the development of a Chemical Oxygen-Iodine Laser (COIL) with alternative chemical ways of generating atomic iodine. Injection of atomic iodine as opposed to molecular iodine has the potential to improve the COIL efficiency. This paper describes two chemical methods for generating iodine atoms based on the gas phase reactions of hydrogen/deuterium iodide with fluorine or chlorine atoms, which are also produced chemically. Simplified one-dimensional gas dynamic modeling that describes the stream-wise profiles of species concentrations within both reaction systems is used to gain a theoretical understanding of both reaction systems under COIL conditions. The modeling results are used for the design of an experimental device and the interpretation of experimental data. The first experimental investigation studies the production of iodine atoms produced from reactions of Cl with HI. Atomic iodine yields of 70–100% in nitrogen are obtained, and the gain on the I(² P _1/2)–I(² P _3/2) transition in a flow of singlet oxygen is measured. Received: 7 October 2002 / Accepted: 8 February 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +420-2/8689-0527, E-mail: kodym@fzu.cz     

Novel concept of electric discharge oxygen-iodine laser

A novel concept of discharge oxygen-iodine laser (DOIL) is presented. The supersonic DOIL includes a discharge singlet oxygen generator (DSOG) and discharge atomic iodine generator (DAIG). The operation of DSOG is based on a fast mixing of hybrid argon plasma jet of DC electric arc and RF discharge with a neutral molecular oxygen stream. The goal of our effort is achievement of DOIL oscillations by this new discharge technique, which should provide the singlet oxygen yields exceeding 30% at the total pressures higher than 10 torr. The DAIG operation is based on a cw/pulse RF discharge dissociation of iodine donors directly inside a laser iodine injector. This method substitutes the classic dissociation of molecular iodine by energy of singlet oxygen, which saves its energy for laser generation and so can increase the laser efficiency. The laser power could be thus enhanced by up to 25% if this method is employed in a chemical oxygen-iodine laser (COIL) operation, and even 3 times in DOIL without increase in the iodine laser pumping by singlet oxygen.     

Minimization of the photolysis-driven density gradients by slow pumping in the iodine laser amplifier with regard to the beam quality

The UV photolytical pumping of perfluoralkyl iodides C₃F₇I in the large atomic iodine laser amplifier gives rise to density waves in the gas mixture. The increasing gas temperature during photolysis contributes to the increase of the sound wave velocities. Our calculations of the time interval during which the influence of the oscillating part of the gradient of the refractive index on the focusability was at a minimum was made at a constant gas temperature, which was regarded as a parameter. The results are given in a nomographic chart for various parts of He and SF₆ in gas mixture and for various laser tube diameters. The applicability of a heavier buffer gas-argon and a lighter iodine CF₃I considering the sound waves velocities was investigated.The authors wish to thank dr. K. Rohlena for many useful discussions.     

Raman spectrum and cross sections of n-C3F7I. Implications for a large-scale atomic iodine laser

The Raman spectrum of gaseous n-C₃F₇I has been recorded.Raman cross sections, depolarization ratios, and line widths were measured for the four strongest Raman-active modes. Using the measured values for the 280 cm^-1 mode, the stimulated-Raman gain for a large-scale iodine laser was calculated. The results indicate that losses due to stimulated-Raman scattering will be negligible for a fusion-driver iodine laser.     

Chemical oxygen-iodine laser with external production of iodine atoms in CH3I/Ar dc glow discharge

A cw chemical oxygen-iodine laser (COIL) operating in a subsonic mode with a high water content of ～15% and external production of iodine atoms in CH₃I/Ar dc glow discharge has been demonstrated. A straightforward comparison of COIL performance for two cases—conventional, when I₂ was injected in the singlet oxygen flow, and when iodine atoms produced externally together with other discharge products were injected—was made. In the latter case nearly four times increase in output power was observed, suggesting that the relaxation of the energy stored in the singlet oxygen slowed down substantially, when the laser operated using CH₃I/Ar discharge products instead of iodine molecules.     

On-line computer controlled cw dye laser spectrometer for laser isotope separation

An on-line cw dye laser multichannel spectrometer is described, which can be controlled by FORTRAN. Automatic tuning of a dye laser to the wavelength of maximum excitation selectivity for photochemical isotope separation is achieved. Applying the system to the selective photoaddition of iodine chloride ICl to acetylene, an enrichment factor of³⁷Cl in the photoproduct C₂H₂ICl of β=100±5 was obtained. Both stable chlorine isotopes can be enriched to more than 97% purity in a single step, starting from natural samples in both cases.