Laser-induced Fluorescence Emission Research Articles

Studies on the plasma localization of a magnetic neutral loop discharge using normalized radio frequency electric field

In order to establish the conditions required for the formation of a neutral loop discharge (NLD) plasma, the distributions of excited atoms that are closely related to that of the ionization rates were measured under various discharge conditions. Also, computer-based simulations in three dimensions were used to examine the experimental results obtained. The measurements of the distributions of excited atoms were performed using laser-induced fluorescence and optical emission spectroscopy(s). The results of the measurements were consistent with the theoretically predicted dependencies of electron heating on the magnetic field strength, electric field, frequency and NL radius. In addition, it was found that the plasma localization increased with the normalized rf electric field (F0), which can be used to characterize the localization degree of the plasma production region.

Exploring the Bermuda triangle of homonuclear diatomic spectroscopy: The electronic spectrum and structure of Ge2

The optical spectrum of jet-cooled Ge2 has been observed for the first time. Laser-induced fluorescence (LIF) and wavelength resolved emission spectra were recorded using the pulsed discharge technique with a tetramethylgermane precursor. Analysis of the spectra yielded the vibrational constants ωe″=287.9(47), ωexe″=0.81(55), ωeye″=0.0037(18), ωe′=189.0(15), ωexe′=6.41(30), and Te′=20 610.8(16) cm−1. High-resolution rotationally resolved spectra of several bands of Ge274 show two strong P and R branches and two very weak Q branches. We have assigned the band system as a Hund’s case (c) Ω′=1−Ω″=1 transition from the ground Σg−3 state to a Σu−3 excited state. The bond lengths derived from the rotational constants are r0″=2.3680(1) Å and re′=2.5244(18) Å, an ∼0.16 Å increase on electronic excitation. Arguments are presented for assigning the transition to a σg2πu2→σg2πuπg electron promotion, although the observed increase in the bond length is much less than predicted by previous ab initio calculations. The absence of the 0u+–0g+ component in the spectra has been attributed to an excited state predissociation.

Applications of autofluorescence for characterisation of biological systems (biomonitoring).

We describe a system capable of measuring the laser induced fluorescence emission of two coenzymes (NADH and FAD) via an optical fibre for in vivo monitoring of anatomical, physiological or pathological changes in biological systems. This optical technique permits the measurement of changes in the metabolism of cells in real-time and is nearly non-destructive. We present results of examinations on the localisation of transitions between different tissue and the monitoring of the oxygenation level (ischemia) in muscle or changes in the cellular activity of bacteria in a bioreactor.

Low-frequency large-amplitude vibrations of julolidine in the S 0 and S 1 states

The vibrational modes of julolidine in the ground- and the first-excited states have been investigated by laser-induced fluorescence (LIF), multiphoton ionization (MPI) and dispersed emission spectroscopy. In the observed LIF excitation spectrum the mode 140 cm −1 appears and is assigned to the N-inversion mode of the S 1 state which gets coupled with the ring puckering modes of the fused saturated six-membered ring. A progression of 148 cm −1 intervals appears in the dispersed emission spectra, which on the basis of semi-empirical calculations has been identified as the N-inversion mode of the ground state.

A measurement method of absolute hydrogen atom density in plasmas by (2+1)-photon laser-induced fluorescence spectroscopy

A technique of (2+1)-photon laser-induced fluorescence (LIF) spectroscopy has been developed for measuring hydrogen atom density in plasmas. In this method, the following two-step excitation scheme is employed to excite ground-state H atoms to the 4p state. In the first step, H atoms at the ground (1s) state are excited to the 2s state by two photons at a wavelength of 243 nm. Subsequently, the 2s state is excited to the 4p state by the third photon at 486 nm in the second step. Fluorescence emission at 486 nm (4p→2s, Hβ line) is detected to determine the H atom density at the ground state. Since the wavelength used in the first-step excitation is the half of the wavelength used in the second-step excitation, one tunable laser with a system for second harmonic generation can be utilized in the measurement. The absolute density was evaluated by comparing the intensity of LIF emission from H with that from Xe at a known gas pressure. The present method is suitable for diagnostics of reactive plasmas since optical dissociation of molecules and radicals can be avoided because of the low photon energy of the laser radiation.

A study of N,N′-dicarboxyalkylthiacarbocyanines as cyanine direactive dyes covalently bound to cellulose

The synthesis of N,N′-dicarboxyalkylthiacarbocyanines and their spectroscopic properties before and fixation to microcrystalline cellulose are described. Fixation yields were determined by FTIR spectroscopy, giving an alternative to the classical indirect spectroscopic method that uses the ratio of the areas of the absorption bands for cellulose and fixed dye. Diffuse reflectance spectrometry was used to compare chemically bound dye on cellulose to physically adsorbed dye. These results, in tandem with laser induced fluorescence emission data, revealed the formation of aggregates and considerable molecular distortion, the latter resulting from a decrease in molar absorptivity compared to the case in which the dye is physically absorbed.

Electronic spectroscopy of B atoms and B2 molecules isolated in para-H2, normal-D2, Ne, Ar, Kr, and Xe matrices

We report spectroscopic observations on B atoms isolated in cryogenic parahydrogen (pH2), normal deuterium (nD2), Ne, Ar, Kr, and Xe matrices, and of B2 molecules in Ne, Ar, Kr, and Xe matrices. The 2s23s(2S)←2s22p(2P) B atom Rydberg absorption suffers large gas-to-matrix blue shifts, increasing from +3000 to +7000 cm−1 in the host sequence: Xe<Kr<Ar≈Ne≈nD2≈pH2. Much smaller shifts are observed for the 2s2p2(2D)←2s22p(2P) B atom core-to-valence transition. We assign pairs of absorption peaks spaced by ≈10 nm in the 315–355 nm region to the B2 (A 3Σu−←X 3Σg−) Douglas–Herzberg transition. We assign a much weaker progression in the 260–300 nm region to the B2 (2)3Πu←X 3Σg− transition. We report a novel progression of strong peaks in the 180–200 nm region which we suspect may be due to B2 molecules, but which remains unassigned. Ultraviolet (UV) absorption spectra of B/pH2 solids show two strong peaks at 216.6 and 208.9 nm, which we assign to the matrix perturbed 2s23s(2S)←2s22p(2P) and 2s2p2(2D)←2s22p(2P) B atom absorptions, respectively. This assignment is supported by quantum path integral simulations of B/pH2 solids reported in the following article in this journal [J. R. Krumrine, S. Jang, G. A. Voth, and M. H. Alexander, J. Chem. Phys. 113, 9079 (2000)]. Laser induced fluorescence emission spectra of B/pH2 solids show a single line at 249.6 nm, coincident with the gas phase wavelength of the 2s23s(2S)→2s22p(2P) B atom emission. The UV laser irradiation results in photobleaching of the B atom emission and absorptions, accompanied by the formation of B2H6.

Probability distribution of laser-induced breakdown and ignition of ammonia

Laser-induced breakdown and ignition of atmospheric pressure ammonia and ammonia/oxygen mixtures were studied using a nominal 7-ns pulsed Nd : YAG laser source. The probability distribution functions (pdf) for the breakdown and ignition events were determined. For the pdf measurements, the NH-radical ground electronic state was observed using resonant laser-induced fluorescence (LIF), and comparison of the LIF and spontaneous emission of the NH A-state emission is shown. The NH X-state concentration is shown to give a reliable indicator of ignition at 5 μ s following breakdown.

Tensor density matrix theory for determining population and alignment of symmetric top molecule using rotationally unresolved fluorescence

General expressions used for transforming raw laser-induced fluorescence (LIF) intensity into the population and alignment parameters of a symmetric top molecule are derived by employing the density matrix approach. The molecular population and alignment are described by molecular state multipoles. The results are presented for a general excitation-detection geometry and then applied to some special geometries. In general cases, the LIF intensity is a complex function of the initial molecular state multipoles, the dynamic factors and the excitation-detection geometrical factors. It contains a population and 14 alignment multipoles. How to extract all initial state multipoles from the rotationally unresolved emission LIF intensity is discussed in detail.

Characteristics of Laser-Ablated Plasma and Properties Of Diamond-Like Carbon Film In Pulsed Laser Deposition

AbstractCharacteristics of laser-ablated carbon plasma and properties of diamond-like carbon film in KrF pulsed laser deposition were investigated using laser-induced fluorescence (LIF) and optical emission spectroscopy. Two-dimensional LIF images of C2 (Swan band, d3Φg – a3Φu) and C3 (Comet Head System, A1Φu –X1Σg+) molecules were detected as a function of laser energy density by narrow band pass filters and an intensified CCD camera. C2 LIF intensity is found to be weaker in the central part of the plume than that at the periphery at incident energy greater than 6 J/cm2. It is conjectured that C2 molecules are dissociated by collision with energetic species in the central part of the ablation plume, and degrade the diamond-like property of deposited films.

Photophysics of Cyanine Dyes on Surfaces: Laser-Induced Photoisomer Emission of 3,3'-Dialkylthiacarbocyanines Adsorbed on Microcrystalline Cellulose

The photophysics of three thiacarbocyanine dyes, 3,3'-dimethylthiacarbocyanine iodide (DMTCC), 3,3'-diethylthiacarbocyanine iodide (DETCC), and 3,3′-dipropylthiacarbocyanine iodide (DPTCC) was studied when adsorbed on microcrystalline cellulose in the concentration range from 5.0 · 10-4 to 10.0 μmol g-1. Using ground-state diffuse reflectance absorption technique, only H aggregate formation was detected for all the probes. The amount of aggregate formed depends on the hydration degree of the sample, always decreasing with sample dryness. The fluorescence quantum yields for all the adsorbed dyes are one order of magnitude higher than those observed in nonviscous solvents, being 0.98 for DMTCC, 0.96 for DETCC, and 0.63 for DPTCC. Laser-induced fluorescence emissions were recorded (using an intensified-charge-coupled-device detection system) as a function of the laser power, showing that for dry concentrated samples irradiated with high laser intensity, a second fluorescence emission band (bathochromically shifted relative to the monomer emission) was detected. This emission shows a supralinear dependence on laser power. The new emissions here detected arise from fluorescent photoisomers formed via singlet monomers, by a two-photon absorption process.

Detection of transplant vasculopathy in a rat aortic allograft model by fluorescence spectroscopic optical analysis.

Transplant vasculopathy is a leading cause of late cardiac graft loss. We have examined laser-induced fluorescence (LIF) spectroscopy as an optical diagnostic tool for detection of intimal plaque development and inflammatory cellular invasion in a rat model of aortic allograft transplant. Infrarenal aortic segments were transplanted from Lewis to Sprague Dawley rats. A range of vasculopathy development was produced by treatment with a viral anti-inflammatory protein. LIF spectra were recorded from the intima of aortic implants at 28 days. Fluorescence intensity was analyzed for correlation with vasculopathy development. Significant differences in LIF intensity at 400-450 nm (P < or = 0.05 by ANOVA) were detected. LIF emission was correlated with plaque growth (R2 = 0.980), vessel narrowing (R2 = 0.964), and cellular invasion (R2 = 0.971) by regression analysis. LIF optical analysis provides a nontraumatic diagnostic approach for detection of atherosclerosis prior to cardiac transplant or during development of vasculopathy after transplant.

Design and application of a lidar fluorosensor system for remote monitoring of phytoplankton

A characterization of diVerent phytoplankton cultures has been carried out in the laboratory in combination with laser-induced fluorescence (LIF) measurements aimed at investigating the possibility of remote monitoring by means of lidar fluorosensor systems. Cultures of microalgae characterized by diVerent pigment contents were analysed in the visible region on near UV laser excitation. The measured spectra allowed us to obtain a fingerprint of each species and to identify the emission wavelengths in relation to the main pigment contents. The remote-sensing apparatus was upgraded with a double-pulse laser source to test the eVectiveness of a LIF technique based on a pump-and-probe laser excitation scheme suitable for directly measuring the algal quantum yield. In combination with photosynthetic active radiation, the electron transport rate of the investigated phytoplankton was obtained directly in the sea water. The instrumentation for local and remote analysis of phytoplankton was applied at the ICES/IOC workshop at the Kristineberg Marine Research Station (Sweden, 9‐15 September 1996), where the LIF emission of natural communities and cultures has been monitored in vivo obtaining information on the algae species present and on their photosynthetic activity. ? 1998 International Council for the Exploration of the Sea

Spatial variability of oceanic phycoerythrin spectral types derived from airborne laser-induced fluorescence emissions

We report spatial variability of oceanic phycoerythrin spectral types detected by means of a blue spectral shift in airborne laser-induced fluorescence emission. The blue shift of the phycoerythrobilin fluorescence is known from laboratory studies to be induced by phycourobilin chromophore substitution at phycoerythrobilin chromophore sites in some strains of phycoerythrin-containing marine cyanobacteria. The airborne 532-nm laser-induced phycoerythrin fluorescence of the upper oceanic volume showed distinct segregation of cyanobacterial chromophore types in a flight transect from coastal water to the Sargasso Sea in the western North Atlantic. High phycourobilin levels were restricted to the oceanic (oligotrophic) end of the flight transect, in agreement with historical ship findings. These remotely observed phycoerythrin spectral fluorescence shifts have the potential to permit rapid, wide-area studies of the spatial variability of spectrally distinct cyanobacteria, especially across interfacial regions of coastal and oceanic water masses. Airborne laser-induced phytoplankton spectral fluorescence observations also further the development of satellite algorithms for passive detection of phytoplankton pigments. Optical modifications to the NASA Airborne Oceanographic Lidar are briefly described that permitted observation of the fluorescence spectral shifts.

Autofluorescence Bronchoscopy in the Detection of Squamous Metaplasia and Dysplasia in Current and Former Smokers

New methods are needed to detect precancerous lesions in lung tissue. We conducted a study to determine the utility of LIFE (laser-induced fluorescence emission) autofluorescence bronchoscopy for the detection of squamous metaplasia and dysplasia in current and former smokers. In this prospective, single-center study, 53 participants underwent standard white-light bronchoscopy and 39 underwent both white-light and LIFE bronchoscopy. Bronchial biopsy specimens were obtained from all participants at six pre-determined sites using white-light bronchoscopy and from all other sites that appeared to be abnormal in participants who underwent LIFE bronchoscopy. Relationships between LIFE imaging and histologic findings were examined for 245 biopsy specimens obtained from those participants who had undergone LIFE bronchoscopy. LIFE imaging revealed abnormalities designated as either class II or class III in 89 (36.3%) and 16 (6.5%) of the 245 sites examined, respectively, and histopathologic examination showed dysplasia and metaplasia in eight (3.3%) and in 52 (21.2%) of the 245 specimens, respectively. Among the 105 biopsy specimens obtained from sites with abnormal LIFE imaging, only 26 (24.8%) exhibited squamous metaplasia and/or dysplasia, similar to the findings for sites with normal LIFE imaging (34 [24.3%] of 140). Comparison of individuals examined by LIFE imaging with those who underwent white-light bronchoscopy alone revealed no increase in the detection of dysplasia or metaplasia with LIFE bronchoscopy. In this population of current and former smokers, abnormalities detected by LIFE bronchoscopy did not improve the detection of squamous metaplasia or dysplasia.

Airborne laser-induced oceanic chlorophyll fluorescence: solar-induced quenching corrections by use of concurrent downwelling irradiance measurements

Airborne laser-induced (and water Raman-normalized) spectral fluorescence emissions from oceanic chlorophyll were obtained during variable downwelling irradiance conditions induced by diurnal variability and patchy clouds. Chlorophyll fluorescence profiles along geographically repeated inbound and outbound flight track lines, separated in time by approximately 3-6 h and subject to overlying cloud movement, were found to be identical after corrections made with concurrent downwelling irradiance measurements. The corrections were accomplished by a mathematical model containing an exponential of the ratio of the instantaneous-to-average downwelling irradiance. Concurrent laser-induced phycoerythrin fluorescence and chromophoric dissolved organic matter fluorescence were found to be invariant to downwelling irradiance and thus, along with sea-surface temperature, established the near constancy of the oceanic surface layer during the experiment and validated the need for chlorophyll fluorescence quenching corrections over wide areas of the ocean.

Spectroscopy and dynamics of jet-cooled 2-methoxynaphthalene

The S 1−S 0 electronic transition of jet-cooled 2-methoxynaphthalene has been investigated by the use of laser-induced fluorescence, dispersed fluorescence and time-resolved emission spectroscopy. Two electronic origin transitions were observed, separated by 660 cm −1. They are caused by the presence of a cis (syn) and a trans (anti) conformation of the methoxy group with respect to the naphthalene frame. Intramolecular vibrational energy redistribution was identified by vibrational quantum beats in the case of the cis isomer 978 cm −1 above the S 1−S 0 origin.

Laser-Induced Fluorescence Spectroscopy of Jet-Cooled Benzophenone Ketyl Radical

The D1 ← D0 transition of jet-cooled benzophenone ketyl radical (BPK) and its deuteride was studied by using laser-induced fluorescence (LIF) spectroscopy. BPK was generated by the 248 nm photolysis of α-phenylbenzoin, and its vibrationally resolved LIF excitation and emission spectra were obtained for the first time. The 18 451 cm-1 band was assigned to the band of the D1 ← D0 transition of BPK. Two vibrational modes of BPK with 65 and 84 cm-1 in the first excited state were assigned to the in-phase and out-of-phase torsional motions of the phenyl rings, respectively. The vibrational mode with 980 cm-1 was tentatively assigned to the C−O stretching mode. The mode of 74 cm-1 in the ground state was assigned to the in-phase torsional mode. It was confirmed that the torsional motions do not couple with the C−O stretching and O−H rotational motions. The force field analysis and the simple Franck−Condon calculation were made. The measured fluorescence lifetimes of BPK and its deuteride are short and consistent with those in the gas and liquid phases at room temperature.

Electronic states of Bi2

Laser-induced fluorescence and thermal emission spectra of Bi2 have been recorded at high resolution by Fourier transform spectrometry. Extensive analyses, involving the assignment of more than 20 000 lines, have been made of transitions involving the states X 0+ g, a lu(3Σ+ u), A 0+ u(3Σ- u) and E lg. The electronic states of Bi2 are reviewed, and comparison is made with the results of ab initio calculations.

Plif imaging measurements of a co-axial rocket injector spray at elevated pressure

A small-scale rocket combustion chamber has been developed for fundamental investigations on liquid oxygen/gaseous hydrogen (LOX/GH2) combustion under high-pressure conditions. The combustion chamber is designed for pressures up to 2M Pa equipped with a unielement shear co-axual injector. The intention of the experimental work is to apply optical diagnostic techniques to show their feasibility in two-phase high-pressure flows and to characterize the phenomenology of the LOX/GH2 spray flamelike liquid oxygen injection, atomization, evaporation, turbulent mixing, and combustion. Planar laser-induced predissociation fluorescence (PLIPF) and spontaneous emission of OH have been applied at three different chamber pressures in the near field of a shear co-axial injector in the optically accessible rocket chamber. Single shot and averaged images have been measured to map the flame zone, delivering qualitative information of the reactive flow field. Additionally, dispersed fluorescence spectra of OH in the wavelength range of the A2(v′=3)←X2H (v″=2) fluorescence band have been measured to evaluate interferential effects arising from O2 that occur with increasing chamber pressures.