Diffusion of resonance radiation in atomic vapor imaging

The effect of resonance radiation diffusion due to radiation trapping has been studied in an atomic vapor imaging filter. Using a cesium resonance fluorescence imaging monochromator, the spatial distortions due to resonance radiation trapping by Cs atoms in the pumping/imaging region have been investigated. It was found that the spatial distortions were dependent on the number density of the Cs atoms, as well as the irradiance of the signal photons at 852.12 nm (6²S_1/2→6²P^o_3/2). The pump laser (917.23 nm, 6²P^o_3/2→6²D_5/2) did not influence the radiation diffusion to the same degree as the signal beam. It is shown that there is a compromise between maximum optical density and spatial resolution. The number density of the Cs resonance fluorescence imaging monochromator was optimized to obtain the highest spatial resolution and signal-to-background ratio.     

Ionization-induced nucleation above liquid beam of aqueous solution of phenol after IR laser irradiation

A continuous liquid flow of an aqueous solution of phenol (Ph) in a vacuum (a liquid beam) was irradiated with a pulsed IR laser at 3 μm, which was resonant to the OH-stretching vibration of the solvent water molecules. Phenol molecules ejected from the liquid beam were selectively ionized at about 0.5 mm above it by a pulsed UV laser (270–280 nm). The photoions thus produced were extracted in a pulsed electric field with a given residence time after the photoionization for mass analysis. It was shown that photoions, Ph⁺, were solvated into Ph⁺(H₂O)_n in a dense cloud of water vapor ejected from the liquid beam by IR irradiation.     

Continuous flow hydride generation laser induced fluorescence spectrometry for trace determination of lead in water and sediment samples

Continuous flow hydride generation coupled with laser induced fluorescence spectrometry (HG-LIF) has been used for the determination of Pb in aqueous samples. Lead hydride is generated in K₃Fe(CN)₆-HCl medium using NaBH₄ as the reducing agent. Parameters such as acidity and the concentrations of oxidising and reducing agents have been studied in order to obtain the highest sensitivity. Laser excitation of Pb has been performed at 283.306 nm and fluorescence has been detected at 365 nm and 405.8 nm. The limit of detection calculated for the optimised conditions (1% K₃Fe(CN)₆ in 0.3% Oxalic Acid, 0.055 mol L^?1 HCl, 1% NaBH₄ in 0.1% NaOH) is 0.3 ng mL^?1. However, a significant Pb background was observed for blank measurements, which degraded the limit of detection. The limit of detection that is estimated for a Pb free blank was determined by detuning the laser to a wavelength of 282.806 nm and was found to be 0.45 pg mL^?1. Method repeatability is 3.5% RSD at the 10 ng mL^?1 level. The accuracy of this method has been evaluated by analysis of a water reference material. The results obtained for a multielement standard determined using the HG-LIF approach have been found to be in agreement with those obtained by using a comparison ICP-AES approach. The HG-LIF approach has been applied to the measurement of Pb in a contaminated sediment sample material. The results of this study demonstrate that a small tunable laser system combined with hydride generation sample introduction can be used to measure Pb with high sensitivity, precision and selectivity in different sample matrices.     

Measurements of light scattering changes induced by a strong optical field in solutions of tRNA

Changes in light scattering induced by a strong laser beam, as predicted theoretically by Kielich, were measured for unfractionated yeast transfer ribonucleic acid (tRNA) solutions. The vertically polarized electric field of a strong laser pulse (λ = 1060nm) amounted to 4.5 × 10³ esu cgs; its duration was 10 nsec. A weak incident laser beam (λ = 630nm) was also polarized vertically and the vertical and horizontal intensity components of the light scattered through 90° at the latter wavelength were measured. These measurements together with previous results from measurements of Rayleigh light scattering and light scattering in a magnetic field permitted evaluation of the tensor of third-order polarizability (c = 3 × 10^?30 esu cgs, c = ?373 × 10^?30 esu cgs) and the anisotropy of the third-order polarizability components with its sign (δ_c = +56 × 10^?2, δ_c = +0.25 × 10^?2 for tRNA monomer and aggregate, respectively). The new method described may be useful for studies of macromolecules and macromolecular complexes of biological importance.     

Ultrasensitive determination of gold in geogas by laser excited atomic fluorescence spectrometry

Ultratrace gold (Au) in geogas samples has been determined by means of laser excited atomic fluorescence spectrometry combined with graphite electrothermal atomization and time-gate technique. Gold atoms were excited from the ground state to the 6p²P_3/2 state by a pulsed laser beam with a wavelength of 242.8 nm. Fluorescence photons with a wavelength of 312.3 nm were measured by a photon-counting unit. The time-gate technique was used to reduce the background radiation caused by the furnace. This method has proved to be highly sensitive with minimal background interference. Eighty-two geogas samples were analysed and the Au contents obtained were in the range of 0.002–0.182 ng l⁻¹. The study of Au concentration of geogas in soil is of great interest in prospecting gold deposits.     

Visible Up-Conversion Luminescence in Ho3+: BaTiO3 Nano-Crystals Prepared by Sol Gel Technique

Visible up-conversion emissions at (435, 545, 580, 675 and 690 nm) and (437, 547 575 and 675 nm) have been observed from the sol-gel derived nano-crystalline Ho³⁺: BaTiO₃ powders and thin films respectively, under 808 nm laser diode excitation emissions. Combined with the energy level structure of Ho³⁺ ions and the kinetics of the visible emissions, the up-conversion mechanism has been analyzed and explained. The blue, green and red emissions of both samples has been attributed to the ground state-directed transition from (⁵F₁), (⁵S₂) and (⁵F₅), which are populated through excited state absorption (ESA) for 808 nm excitation. Nano-structure pure barium titanate and doped with different concentrations of Ho³⁺ ions in the from of powder and thin film have been prepared by sol-gel technique, using barium acetate (Ba(Ac)₂), and titanium butoxide (Ti(C₄H₉O)₄), as precursors. The thin films were prepared by sol-gel spin coating method. The as-grown thin films and powders were found to be amorphous, which crystallized to the tetragonal phase after heating at 750°C in air for 30 minutes. The crystallite sizes of the thin film and powder both doped with 4% Ho³⁺ ions was found to be equal to 11 and 16 nm, respectvely.     

Effect of Medium Acidity and Photostability of 3‐(4‐Dimethylamino‐phenyl)‐1‐(2,5‐dimethyl‐thiophen‐3‐yl)‐propenone (DDTP): A New Green Emitting Laser Dye

On the line of a previous work on the spectral properties of some of heteroaryl chalcone, the effect of medium acidity and photoreactivity of 3‐(4‐dimethylamino‐phenyl)‐1‐(2,5‐dimethyl‐thiophen‐3‐yl)‐propenone (DDTP) has been investigated in dimethylformamide and in chloromethane solvents such as methylenechloride, chloroform and carbon tetrachloride. The dye solution (ca. 5×10⁻⁴ mol·L⁻¹ in DMF) gives a good laser emission in the range 470–560 nm with emission maximum at 515 nm upon pumping by nitrogen laser (λ_ex=337.1 nm). The laser parameters such as gain coefficient (α), emission cross section (δ_e) and half life energy (E_1/2) at maximum laser emission are also determined.     

Syntheses and characterization of three mercury(II) complexes, [Hg(phen)2(SCN)2], [Hg(2,2′-bipy)2(SCN)2] and [Hg(phen)2(NO3)2], thermal and fluorescence studies

Mercury(II) complexes of 1,10-phenanthroline (phen) and 2,2′-bipyridine (bipy), [Hg(phen)₂(SCN)₂] (1), [Hg(2,2′-bipy)₂(SCN)₂] (2) and [Hg(phen)₂(NO₃)₂] (3) have been synthesized and characterized by elemental analysis, IR, ¹H NMR and ¹³C NMR spectroscopy. The thermal stability of 1–3 were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The structure of 1 has been confirmed by X-ray crystallography. The complex is a monomer and the Hg atom has an unsymmetrical six-coordinate geometry, formed by four nitrogen atoms of the two phen ligands and two sulfur atoms of the two thiocyanate anions. Solid-state luminescent spectra of phen, 2,2′-bipy and 1–3 indicate emission with the maximum intensity at ca 467 nm upon excitation at 295 nm.     

Experimental transition probability for theE1 intercombination transition in Be-like Xe50+

The 2s^{2 1}S₀ — 2s2p³P°₁ intercombination transition in Be-like Xe⁵⁰⁺ has been observed and the intensity decay with time has been measured using a foil-excited fast ion beam. The transition wavelength value is found to be λ = (9.81±0.05) nm and the upper level lifetime to be τ = (0.47±0.05) ns. Both values agree with recent theoretical predictions.     

Dye laser-induced photodetachment of electrons from SH− studied by ion cyclotron resonance spectroscopy

The photodetachment of electrons from gaseous SH^? ions has been studied in an ion cyclotron resonance mass spectrometer using a flashlamp-pumped organic dye laser as a light source. The onset of the photodetachment process at 538.7 ± 0.3 nm (2.301₆ ± 0.001₃ eV, 18563 ± 10 cm^?1) agrees well with that obtained in an earlier study. Coarse structure in the photodetachment curve with a spacing of 11.8 nm (0.052 eV, 422 cm^?1) has been identified with spin-orbit coupling in the SH^. radical. Finer structure, with a spacing of ca. 2.5 nm (0.011 eV, 89 cm^?1), has also been observed in the curve, but remains unexplained.     

Pulsed,Crossed, Supersonic Molecular Beam Studies of Refractory Atom Reactions

Dynamics of refractory atom reactions have been studied with a crossed beam apparatus combining two pulsed, supersonic molecular beam sources, a pulsed UV laser for creating the refractory atoms in the gas phase by laser ablation, and a pulsed dye laser to probe the reaction products by laser-induced fluorescence. Examples of the A1(²P_j) + O₂(X³∑_g)→ A10(X²∑⁺) + O(³P_j), Mg(¹S_o) + N₂O(X¹∑⁺) → MgO(X¹∑⁺,a³Π) + N₂(X¹∑_g⁺) andC(³P_j) + NO(X²Π_r) → CN(X²∑⁺) + 0(³P_j) systems are given. Comparisons with the studies performed using the conventional steady-state beam approach are made.     

Synthesis, characterization and emission properties of quinolin-8-olato chelated ruthenium organometallics

The reaction of Ru(RL¹)(PPh₃)₂(CO)Cl,1, with quinolin-8-ol (HQ) has afforded complexes of the type [Ru(RL²)(PPh₃)₂(CO)(Q)],3, in excellent yield (RL¹ is C₆H₂O-2-CHNHC₆H₄R(p)-3-Me-5, RL² is C₆H₂OH-2-CHNC₆H₄R(p)-3-Me-5 and R is Me, OMe, Cl). In this process, quinolin-8-olato (Q) undergoes five-membered chelation, the iminium-phenolato function tautomerizing to the imine-phenol function. In dichloromethane solution,3 displays a quasireversible3 ⁺/3 couple near 0·50 V vs SCE (3 ⁺ is the ruthenium (III) analogue of3). Coulometrically generated solutions of3 ⁺ display a strong absorption near 395 nm associated with a shoulder near 475 nm and rhombic EPR spectra withg values near 2·55, 2·13, 1·89. Solutions of3 absorb near 415 nm and emit near 510 nm at 298 K and 585 nm at 77 K. The fluorescence is believed to originate from the³MLCT state     

Studies of Sb and Bi cluster produced by laser desorption

Direct production of cations and anions of metal clusters of Sb and Bi by laser evaporation in a vacuum has been studied. Bulk sample substrates are irradiated by 1064, 532 and 355 nm beams at variable intensity, and the ions produced are accelerated and identified by time-of-flight mass spectrometry. At 1064 nm, the cation distributions show that Sb ₃ ⁺ and Bi ₃ ⁺ are the most abundant species, while the monomer and dimer cations are almost non-existent. The anion spectra indicate very low yields of Sb^? and Bi^? with dominant dimer anion species. These patterns persist with laser power variation within the stable operation domain. With lower incident laser wavelength, the mass distributions are modified, favouring the production of the light cluster ions. In no circumstances were Sb and Bi ions withn>5 observed. Many of the observed phenomena can be explained if one assumes that for these elements, clusters withn<6 are formed on the substrate surface. Cluster ions are produced via a prompt desorption process, and are subjected to photon induced reactions due to the same incident laser beam. However, more detailed investigation of the desorption properties will be necessary to confirm such a desorption mechanism.     

The photochemistry of a potential diphenylsilylene precursor. Time-resolved spectroscopic studies of the reactivity of a transient vinylsilirane

The photochemistry of 3,4-dimethyl-1,1-diphenylsilacyclopent-3-ene (2), a potential precursor to diphenylsilylene (SiPh₂), has been studied in hydrocarbon and methanol solution by steady state and laser flash photolysis techniques. The results are consistent with the formation of three major photoproducts: SiPh₂ (ca. 20%), 2,3-dimethyl-1,3-butadiene (DMB; ca. 20%), and 2-methyl-2-(methylethenyl)-1,1-diphenylsilirane (9; ca. 75%), the product of formal photochemical (1,3)-sigmatropic rearrangement of 2. Attempts to detect the silylene by laser flash photolysis were unsuccessful, but the vinylsilirane could be easily detected as a long-lived transient exhibiting λ_max=285 nm and lifetime τ=1.3 s in hexane at 25 ^{^}C. The same spectrum is observed in neat methanol solution, where the lifetime of the species is shortened to τ=36 ms and it is quenched by sodium methoxide and methanesulfonic acid with absolute rate constants of k _MeO-=2.0×10⁶ M⁻¹ s⁻¹ and k_H+ =2.6×10³ M⁻¹ s ⁻¹, respectively. The photochemistry of 2 is compared to that of the corresponding germanium homologue (1), whose photolysis in solution has been previously shown to afford diphenylgermylene and DMB cleanly and in high yields. The corresponding vinylgermirane (11a), though not detectable as a primary photoproduct from 1 in solution, is the exclusive product of photolysis of 1 in a 3-methylpentane glass at 78 K, where it exhibits an essentially identical UV/vis spectrum to that of 9. The rate constant for its unimolecular thermal isomerization to regenerate 1 is three orders of magnitude larger than that of the corresponding process in the homologous vinylsilirane (9) in hydrocarbon solution at 25 ^C.     

Photophysical and photochemical processes of riboflavin (vitamin B2) by means of the transient absorption spectra in aqueous solution

Using time-resolved techniques of 337 and 248 nm laser flash photolysis, the photo physical and photochemical processes of riboflavin (RF, vitamin B₂) were studied in detail in aqueous solution. The excited triplet state of riboflavin (³RF^*) was produced with 337 nm laser, while under 248 nm irradiation, both³RF^* and hydrated electron (e_aq) formed from photoionization could be detected. Photobiological implications have been inferred on the basis of reactivity of³RF^* including energy transfer, electron transfer and hydrogen abstraction. The RF^·+ was generated by oxidation of SO₄ ^·-radical with the aim of confirming the results of photolysis.     

Use of photothermal deflection spectrometry (PDS) for studies of analytes in aqueous solutions

Summary A crossed-beam photothermal deflection spectrophotometer (PDS) instrument was built, evaluated and applied to the determination of lanthanide neodymium. A dye laser filled with rhodamine 6 G and pumped by an argon ion laser at 514 nm was operated with outputs between 4 and 500 mW at the cuvette position and chopped at 2 Hz. The deflection of a He-Ne probe laser beam, crossing the exciting dye laser, was measured by a two-dimensional position sensitive device and two lock-in amplifiers. The setup was evaluated with a solid carbon sample and the liquids toluene and Nd³⁺/HClO₄.A calibration curve for Nd³⁺ in HClO₄ was obtained and the limit of detection (LOD) for Nd³⁺ was determined to be 2·10^–6 mol/l. This LOD is, on the one hand, by 2 orders of magnitudes lower than the value obtained with the Cary 2400 spectrophotometer and, on the other hand, this transverse PDS technique is highly competitive to collinear thermal lensing and laser-induced photoacoustic spectroscopy.     

Photophysical and photochemical processes of riboflavin (vitamin B2) by means of the transient absorption spectra in aqueous solution

Using time-resolved techniques of 337 and 248 nm laser flash photolysis, the photo physical and photochemical processes of riboflavin (RF, vitamin B₂) were studied in detail in aqueous solution. The excited triplet state of riboflavin (³RF^*) was produced with 337 nm laser, while under 248 nm irradiation, both³RF^* and hydrated electron (e_aq) formed from photoionization could be detected. Photobiological implications have been inferred on the basis of reactivity of³RF^* including energy transfer, electron transfer and hydrogen abstraction. The RF^·+ was generated by oxidation of SO₄ ^·-radical with the aim of confirming the results of photolysis.     

Laser photolysis of C2H2 and CF3C2H at 193 nm: Production of C2(d3Πg and CH(A2Δ) and their quenching by Xe

The 193 nm laser photodissociation of CH₂H₂ and CF₃C₂H has been studied. With the laser beam focused, C₂(d³Π_g) and CH(A²Δ) radicals were formed by multiphoton processes in both C₂H₂ and CF₃C₂H; however, the one-photon process forming C₂H is still predominant in CF₃C₂H photolysis. The production of C₂(d³Π_g) and CH(A²Δ) emissions is prompt,and the emission intensities show similar (less than quadratic) dependence on laser power whether the radicals are produced from C₂H₂ or CF₃C₂H. In addition, the vibrational distribution of the Swan system is nearly the same in CF₃C₂H as in C₂H₂. The results indicate that the overall photolytic processes are similar in two molecules. Both the C₂(d³Π_g) and CH(A²Δ) emissions are quenched by Xe with rate constants of 4.8×10^?11 and 1.8×10^?11 cm³ molecule^?1 s^?1, respectively.     

Near-infrared range photorefractive composites based on poly(vinylcarbazole), multiwall carbon nanotubes, and fullerene C60 1

For composites based on poly(vinylcarbazole) and multiwall carbon nanotubes, photorefractive characteristics at 1064 nm have been studied in the presence and absence of fullerene C₆₀. It has been found that the introduction of fullerene C₆₀ provides an increase in the two-beam gain coefficient of a laser beam and a reduction in the time of hologram recording. The preillumination of the fullerene-containing layer with a continuous light from a He-Ne laser (633 nm) leads to an additional increase in the two-beam gain coefficient.     

Isotope ratio analysis on micron-sized particles in complex matrices by Laser Ablation-Absorption Ratio Spectrometry

Laser ablation has been combined with dual tunable diode laser absorption spectrometry to measure ¹⁵²Gd:¹⁶⁰Gd isotope ratios in micron-size particles. The diode lasers are tuned to specific isotopes in two different atomic transitions at 405.9 nm (¹⁵²Gd) and 413.4 nm (¹⁶⁰Gd) and directed collinearly through the laser ablation plume, separated on a diffraction grating, and detected with photodiodes to monitor transient absorption signals on a shot-by-shot basis. The method has been characterized first using Gd metal foil and then with particles of GdCl₃·xH₂0 as binary and ternary mixtures with ¹⁵²Gd:¹⁶⁰Gd isotope ratios ranging from 0.01 to 0.43. These particulate mixtures have been diluted with Columbia River sediment powder (SRM 4350B) to simulate environmental samples and we show the method is capable of detecting a few highly-enriched particles in the presence of a >100-fold excess of low-enrichment particles, even when the Gd-bearing particles are a minor component (0.08%) in the SRM powder and widely dispersed (1178 particles detected in 800,000 ablation laser shots). The implications for monitoring ²³⁵U:²³⁸U enrichment ratios in airborne particle samples, as related to the nuclear industry, are discussed.