Laser-induced fluorescence thermometry and concentration measurements on NOA–X (0-0) transitions in the exhaust gas of high pressure CH4/air flames

Laser-Induced Fluorescence (LIF) excitation spectra in the NOA–X (0-0) band were used for temperature measurements in the postflame region of high-pressure CH₄/air flames. To improve the quality of the measured spectra and to perform reliable line-shape measurements, the initial mixture was doped with approximately 400 ppm NO. At pressures up to 18 bar, excellent agreement was obtained between NO LIF temperatures and NARS/rotational Raman temperatures. Effective broadening coefficients were also determined in these flames. Problems with quantitative concentration measurements of NO and single-pulse temperature measurements at high pressures are discussed.     

Laser-induced fluorescence detection of acetylene in low-pressure propane and methane flames

Laser-induced fluorescence is used to detect and record profiles of acetylene formed as an intermediate species in 10-Torr premixed propane and methane flames. In low-temperature regions of the flames, excitation spectra confirm acetylene as the spectral carrier. The spectra of acetylene overlap those of O₂ and NO in terms of both excitation and detection wavelengths, however, acetylene can be detected with relatively little interference in the vicinity of 228 nm, using a detection wavelength of 260 nm. The fluorescence lifetime of acetylene in the flame conditions studied is approximately 20 ns, much shorter than the radiative lifetime, due to a high quenching rate for all the colliders investigated. This can be exploited in low-pressure flames to avoid interference from acetylene in monitoring nitric oxide. The acetylene mole fraction in propane flames reaches its peak value at nearly the same location as that of HCO, slightly closer to the burner than the peak CH mole fraction. The acetylene fluorescence signal is easily detected in propane flames over equivalence ratios from 0.6 to 1.2, although it increases under fuel-rich conditions. In methane flames, the acetylene signal is much weaker and is undetectable for fuel-lean conditions. Received: 5 August 2002 / Revised version: 30 September 2002 / Published online: 20 December 2002 RID="*" ID="*"Corresponding author. Fax: +1-202/767-1716, E-mail: brad@code6185.nrl.navy.mil     

Detection of low gas densities by resonance fluorescence in the vacuum ultraviolet

An experimental arrangement is described which allows the detection of low gas densities by resonance fluorescence in the vacuum ultraviolet. As a light source a capillary discharge through helium was used. Fluorescence signals as a function of density have been measured in krypton, deuterium, and hydrogen, and the results have been compared with calculations. Detection limits of 3·10⁹ atoms/cm³ have been obtained.     

Calibration of OH laser-induced fluorescence temperature measurements using thermally dissociated H2O

A method for the calibration of OH temperature measurements using laser-induced fluorescence is demonstrated. The technique depends on the thermal dissociation of water vapor in a furnace. The calibration was demonstrated for the excitation of theA ^{2 +}( = 3) – ² ( = 0) band with a tunable KrF laser. Consistent discrepancies of 3% between calculated and measured temperatures with a standard deviation of 8 % were observed.     

Absolute concentration measurements of C2 in a diamond CVD reactor by laser-induced fluorescence

By use of Laser-Induced Fluorescence (LIF) the absolute concentration of the C₂ radical in a microwave excited diamond chemical vapour deposition plasma has been measured for the first time. LIF spectra of thed ³ _g–a ³ _u (1,0) Swan band near 473 nm were recorded and synthesized theoretically allowing the plasma temperature of 2100 ± 200 K to be inferred. Quenching rates were determined from time-resolved measurements of the fluorescence decay. By calibrating the LIF detection system, using spontaneous Raman scattering in H₂ in the reactor vessel, the absolute concentration of C₂ was determined to be (7.5 ± 1.7) × 10¹⁰ cm^–3. Observations of the C₂ density under varying plasma conditions are reported.     

The application of a raman-shifted tunable KrF excimer laser for laser-induced fluorescence combustion diagnostics

Four wavelength extensions have been investigated by stimulated Raman scattering in hydrogen or deuterium gas of the 248 nm fundamental output of a narrow-band tunable KrF excimer laser. They have been used to acquire laser-induced fluorescence spectra of NO and OH in flames at atmospheric pressure. NO is detected in relatively high rotational states within the -band electronic system at 225 nm. OH was excited at 291.5 nm in the (1–0), at 313 nm in the (1–1) and at 268.5 nm in the predissociative (3–1) band of the ²–² electronic band system, respectively. Prospects of 2D imaging for concentration and temperature measurements in flames using these wavelength extensions are discussed.     

Detection of aromatic pollutants in the environment by using UV-laser-induced fluorescence

Fluorescence spectra, decay times, and detection limits of the 16 US-EPA polycyclic aromatic hydrocarbons (PAH) have been measured and the results are discussed in terms of separability of single PAHs in a multicomponent mixture. The results of a mathematical analysis of a 16-component mixture is presented. Spectra from natural water samples contaminated with gasoline and tar are also presented and the potential and limits of the LIF technique are discussed. Received: 19 March 1998/Revised version: 2 June 1998     

Laser-induced fluorescence of Pb2

Pb₂, which occurs in lead vapor, was studied by the technique of laser-induced fluorescence using single-mode Ar-laser excitation. The fluorescence observed could be classified into the F-X system. Ten progressions involving vibrational quantum numbers v′ = 0?9 and v″ = 0?22 were analyzed. Including collision-induced lines, rotational quantum numbers from J = 25 to J = 300 were observed. The vibrational constants and the numbering of the states had to be reassigned. For the first time rotational constants were determined for the Pb₂ molecule. The internuclear distances of ²⁰⁸Pb₂ in the F and X state are $\text{r = 3.079}\text{A}\text{?}$ and $\text{r}{}_{\mathrm{<mtext>e</mtext>}}\text{= 2.930}\text{A}\text{?}$, respectively. Using the constants derived RKR potentials and Franck-Condon factors were calculated, which confirmed the vibrational assignments and constants.     

Time-resolved spectroscopy of the fluorescence quenching of a donor — acceptor pair by halothane

Donor (anthracene) sensitized acceptor (perylene) fluorescence is quenched more efficiently by halothane than is intrinsic perylene fluorescence. The underlying process of dynamic fluorescence quenching is investigated by time-resolved fluorescence spectroscopy.     

Laser-induced fluorescence of estrogens

Spectra of the laser-induced fluorescence of estrogens—estradiol, estriol, and estrone—were measured under excitation by the fourth harmonic (λ=266 nm) of a Nd:YAG laser. Quantum yields of the fluorescence were evaluated by the relative technique to be 0.107 for estradiol, 0.116 for estriol, and 0.0052 for estrone. The water solution of tryptophan is used as the standard.     

Laser-induced fluorescence of GdO

A semiempirical calculation of the energy level diagram of GdO based on the ligand field theory is presented here. The main frame of the resulting scheme is very simple and should be useful in order to link together the numerous observed systems of GdO. Pulsed dye laser-induced fluorescence experiments made possible the evaluation of some of the ligand field theory predictions, particularly that a Y⁷Σ⁻ level is lying 1840 cm⁻¹ above the X⁹Σ⁻ ground state. The I and II systems are shown to arise from the B⁹Σ⁻-X⁹Σ⁻ and B₁⁷Σ⁻-Y⁷Σ⁻ transitions, respectively. Continous wave laser-excitation spectra have been recorded and rotational analysis of the A⁹Π₄ → X⁹Σ⁻ transition carried out, confirming previous results of N. N. Dmitriev, L. A. Kaledin, E. A. Shenyavkaya, and L. V. Gurvich (Acta Phys. Hung. 55, 467–479 (1984)).     

TEA CO2 laser-induced photodissociation of UF6 via interspecies V-V energy transfer from multiple photon excited halomethanes

The dissociation of UF₆ sensitized by multiple photon excitation of a series of halomethanes: CF₄, CF₃Cl, and CF₂Cl₂ has been investigated. The roles of various experimental parameters like exciting frequency, fluence and pressures of sensitizer/UF₆ on the dissociation yield were studied to examine (1) the characteristics of the sensitizer/UF₆ system and (2) the coupling of vibrational energy between two molecular systems. The efficiency of the energy transfer process was estimated on the basis of long range dipole-dipole interaction to gain an understanding of the dissociation process.     

OH laser-induced fluorescence at high pressures: spectroscopic and two-dimensional measurements exciting the A–X (1,0) transition

Received: 11 January 1996/Revised version: 25 July 1996     

激光诱导血红蛋白分子的多光子荧光

本文首次报道了血红蛋白吸收二个和四个1.06μm的光子后所发射的荧光特性,并分析了其产生的原因。     

Laser-induced thermal desorption mass spectrometry of functionalized silicon surfaces

Functionalization of materials and laser patterning of chemisorbed layers play an increasing role in tailoring and structuring surface properties on the nanoscale. An attractive method of investigating organic functionalizations is laser-induced thermal desorption (LITD). The analysis of well-defined H- and D-terminated Si(1 1 1)-(1 × 1):H(D) surfaces was used to quantify the LITD technique. Moreover, oxidized silicon surfaces were functionalized with trimethylsilyl (TMS) and (3,3,3-trifluoropropyl)-dimethylsilyl (TFP) hydrophobic end groups. The samples were irradiated normal to the surface with focused XeCl laser pulses. The desorbed species were monitored at an oblique angle and their time-of-flight (TOF) distributions were measured with a quadrupole mass analyzer. The TOF temperatures of silicon were calibrated for different laser pulse energies by desorption of H₂ and D₂. In the LITD experiments, the desorption of trimethylsilanol groups was observed for TMS terminations, indicating that essentially the whole molecule desorbs from the surface. The TOF data could be fitted to Maxwellian distributions, providing the desorption yield of the emitted species, their mass, and temperature. On the other hand, several characteristic fragments were found for the TFP-terminated surface. The TOF distributions indicate that the fragments detected with the analyzer derived from different desorbed species.     

Sensitive detection of H2 molecules by two-photon excited laser-induced fluorescence

The sensitive detection of H₂ molecules was demonstrated by means of twophoton excited laser-induces fluorescence spectroscopy with a narrow-band ArF excimer laser. A detection limit of 2×10¹⁴ cm^–3 was obtained with an excitation power of 150 kW. This is already comparable with that obtained by the coherent anti-Stokes Raman scattering (CARS). This technique was successfully applied to measure a spatial distribution of H₂ in a town-gas burner.     

Laser-induced oxidation of the Si(111) surface

Pulsed laser induced oxidation of clean Si(111) surfaces has been studied by Auger electron spectroscopy and electron energy loss spectroscopy. The short duration time of the pulse has allowed a precise investigation of the first stages of the oxidation. About 1–2 oxide monolayers first grow in less than 10 s. Their stoichiometry evolves from SiO_x towards SiO₂ with increasing beam energy densities. Once this superficial layer has formed, no evolution is seen with further irradiation, suggesting that oxygen diffusion during the pulse duration cannot sustain the oxide growth.     

Measurement of molecular hydrogen densities by resonance fluorescence

Using a pulsed capilary discharge through helium as a light source fluorescence within the Lyman bands (transitionX ¹ ∑ _g ⁺ →B ¹ ∑ _u ⁺ of molecular hydrogen and deuterium has been investigated. Selecting a narrow spectral range (width ≈ 8 ?) from the continuum radiation with a spectrometer, lines in the wavelength range from 1060 ? to 1110 ? have been excited having a vibrational quantum number υ″=0 in the lower state, and ≦υ′≦4 in the upper state. The fluorescence intensity has been measured as a function of υ′ and of the hydrogen density. Agreement with calculations has been found to be within ±30%. The method at present allows the determination of densities between 10¹⁰ and 10¹⁵ molecules per cm³ with a temporal resolution of 1μs and with a spacial resolution of 0.1 cm³     

Laser-induced fluorescence decays of polyethylene films

The fluorescence lifetime of photo-oxidative emission at 360 nm becomes shorter when stabilizer is added to polyethylene film. A broad emission band at 450 nm is attributed to the emission from a charge transfer complex. The preliminary results show that the quenching of photo-oxidative emission and the fluorescence intensity decay can be used to evaluate the extent of photo-stability of polyethylene films.