共查询到20条相似文献,搜索用时 734 毫秒
1.
A. Brockhinke A.T. Hartlieb K. Kohse-Höinghaus D.R. Crosley 《Applied physics. B, Lasers and optics》1998,67(5):659-665
2 in a flame, excited by a tunable KrF laser near 248 nm. The first comprises several P and R lines of the (1,0) band of the
e 3Πg-a 3Πu Fox–Herzberg system, with fluorescence bands extending past 350 nm. The second is the band head region of the (7,1) band
of the D 1Σu
+←B′ 1Σg
+ system, with fluorescence at 232 nm from D to the X 1Σg
+ ground state. Neither band has been previously observed in any environment. The flame in these experiments is highly sooting,
and the C2 seen here is likely produced by laser vaporization of the soot with subsequent laser photolysis of a C2 precursor. In a rich flame, this fluorescence could cause interferences in other studies such as KrF laser Raman scattering.
Moreover, signal level calculations suggest native C2 near 10 ppm could be readily observed using the Fox–Herzberg excitation. Raman measurements of major species (X≥0.01) in
the same flame, using the KrF laser, are in good agreement with a model prediction.
Received: 2 April 1998/Revised version: 8 June 1998 相似文献
2.
W.G. Bessler C. Schulz T. Lee D.-I. Shin M. Hofmann J.B. Jeffries J. Wolfrum R.K. Hanson 《Applied physics. B, Lasers and optics》2002,75(1):97-102
Planar laser-induced fluorescence (PLIF) images of NO concentration are reported in premixed laminar flames from 1–60 bar
exciting the A-X(0,0) band. The influence of O2 interference and gas composition, the variation with local temperature, and the effect of laser and signal attenuation by
UV light absorption are investigated. Despite choosing a NO excitation and detection scheme with minimum O2-LIF contribution, this interference produces errors of up to 25% in a slightly lean 60 bar flame. The overall dependence
of the inferred NO number density with temperature in the relevant (1200–2500 K) range is low (<±15%) because different effects
cancel. The attenuation of laser and signal light by combustion products CO2 and H2O is frequently neglected, yet such absorption yields errors of up to 40% in our experiment despite the small scale (8 mm
flame diameter). Understanding the dynamic range for each of these corrections provides guidance to minimize errors in single
shot imaging experiments at high pressure.
Received: 13 May 2002 / Published online: 8 August 2002 相似文献
3.
This paper presents experimental evidence that using the KrF excimer laser for quantitative laser-induced fluorescence (LIF)
studies of the OH A-X (3,0) system is highly problematic if the effects of both photobleaching and photochemistry are not included for laser spectral irradiances greater than 20 MW/cm2 cm-1. Pump-probe and time-resolved measurements of the OH LIF signal in an atmospheric pressure, premixed CH4-air flame at low- and high-laser-spectral-irradiance conditions show that a significant amount of OH is produced from photofragments
resulting from the simultaneous 2-photon predissociation of H2O molecules in the C-X system. A 5+2-level rate-equation model that includes the effects of both photobleaching and photochemical
OH production is shown to satisfactorily predict the data using a single adjustable parameter given by the effective, spectrally
integrated 2-photon cross-section of H2O near 248 nm. The time-integrated OH LIF signal was found to depend on both the laser spectral irradiance and the local concentration of H2O. Additionally, use of the KrF excimer laser for 2-line rotational thermometry can produce temperature errors as great as
+550 K at high laser-pulse energies.
Received: 21 August 2000 / Revised version: 30 October 2000 / Published online: 21 February 2001 相似文献
4.
The absorption of OH∗ chemiluminescence and laser-induced fluorescence (LIF) in the exhaust gas of confined premixed laminar CH4/air flames at atmospheric pressure was investigated. One flame was used as source and a second as absorber. OH LIF was excited
in the ν″=0→ν′=1 band of the A–X electronic system around ≈283 nm and spectrally resolved detected in the (0,0) and (1,1) vibrational bands
around 305–320 nm. For OH∗ chemiluminescence, spectrally resolved detection was performed in the wavelength range 280–340 nm. For an absorption path
of 54 mm and at T≈2000 K, signal trapping on the order of 10–40% was observed. Signal trapping was most pronounced in the (0,0) band, as expected
from the thermal population distribution of OH in the electronic ground state. The spectral distribution of the signals and
the wavelength dependence of the signal trapping are addressed in this paper. Implications from the results with respect to
detection strategies and chemiluminescence-based equivalence ratio measurements are discussed. 相似文献
5.
2 +? O2→H2O on polycrystalline Pt foils has been studied by detection of desorbing OH radicals using the Resonance Enhanced Multiphoton
Ionization, REMPI, technique. The measurements were performed at catalyst temperatures of 1000–1400 K and a total pressure
below 10-4 mbar. The studies of OH desorption by REMPI were achieved using a two-photon excitation D2Σ-–X2Π (1–0), followed by one-photon ionization. The ions were detected in a time-of-flight mass spectrometer, TOF-MS, in order
to avoid interference from non-resonantly ionized molecules. By applying TOF-MS, a simultaneous non-resonant ionization and
detection of H2, O2 and H2O was achieved. Recorded REMPI spectra were compared with spectra simulated using known molecular constants. The kinetics
of the reaction derived from the measurements were compared with what was obtained in earlier LIF detection of OH, performed
at higher total reactant pressure using the A–X transition. REMPI TOF-MS is shown to be a complement to LIF for reaction studies
below 5×10-4 mbar total pressure, where LIF is too insensitive for quantification. The reaction kinetics was found to be in agreement
with a theoretic model and previous LIF studies.
Received: 8 March 1996/Revised version: 4 October 1996 相似文献
6.
C. Wang N. Srivastava 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,60(3):465-477
OH radical number density in multiple atmospheric pressure microwave plasma
jets is measured using UV cavity ringdown spectroscopy of the OH (A–X) (0–0) band at 308 nm. The plasma cavity was excited
by a
2.45 GHz microwave
plasma source and plasma jets of 2–12 mm long were generated by using
three different plasma gases, argon (Ar), Ar/N2, and Ar/O2.
Comparative characterization of the plasma jets in terms of plasma shape,
stability, gas temperature, emission intensities of OH, NO, and N2, and
absolute number density of the OH radical was carried out under different
plasma gas flow rates and powers at various locations along the plasma jet
axis. With three different operating gases, the presence of OH radicals in
all of the plasma jets extended to the far downstream. As compared to the
argon plasma jets, the plasma jets formed with Ar/N2 and Ar/O2 are more diffuse and less stable. Plasma gas temperatures along
the jet axis were measured to be in the range of 470–800 K for all of the
jets formed in the different gas mixtures. In each plasma jet, OH number
density decreases along the jet axis from the highest OH density in the
vicinity of the jet tip to the lowest in the far downstream. OH density
ranges from 1.3 × 1012 to 1.1 × 1016, 4.1 ×
1013 to 3.9 × 1015, and 7.0 × 1012 to 4.6
× 1016 molecule/cm3 in the Ar, Ar/N2, and Ar/O2
plasma jets, respectively. The OH density dependence on plasma power and gas
flow rate in the three plasma jets is also investigated. 相似文献
7.
M. Jackson E.M. Telles M.D. Allen K.M. Evenson 《Applied physics. B, Lasers and optics》2001,72(7):815-818
A significantly improved far-infrared laser has been used to generate optically pumped laser emissions from 26 to 150 μm for
CD3OH. Using an X–V-pumping geometry, several new laser emissions have been found for CD3OH. In addition, an increase in power, by factors from 10 to 1000, for many of the previously known shorter-wavelength laser
lines, below 100 μm, has been observed. Frequency measurements for several lines have also been performed and have been reported
to a fractional uncertainty up to ±2×10-7, permitting the spectroscopic assignment of the laser transition. One of the frequency-measured lines, 44.256 μm observed
using the 10R34 pump, has confirmed the assignment of the previously reported FIR emission (n,K;J)=(1,7;20)?(0,8;20)A in the
ground vibrational state.
Received: 26 October 2000 / Published online: 7 February 2001 相似文献
8.
K.M. Evenson Q. Sanford C. Smith J. Sullivan D. Sutton E. Vershure M. Jackson 《Applied physics. B, Lasers and optics》2002,74(6):613-614
The partially deuterated isotopes of methanol, CH2DOH and CHD2OH, have been reinvestigated as sources of far-infrared (FIR) laser emissions using an optically pumped molecular laser (OPML)
system recently designed for wavelengths below 150 μm. With this system, 10 new FIR laser emissions from these isotopes ranging
from 32.8 to 174.6 μm have been discovered. This includes the shortest known OPML emission from CHD2OH, at 32.8 μm. These lines are reported with their operating pressure, polarizations relative to the CO2 pump laser and wavelengths, measured to ±0.5 μm. In addition, polarizations for three previously observed FIR laser lines
from CHD2OH were measured for the first time.
This paper is dedicated to the memory of Dr. K.M. Evenson, a pioneer in the field for his role in the development of optically
pumped molecular lasers and their use in laser frequency measurements and the laser magnetic resonance technique. His scientific
expertise, guidance, mentoring and friendship will be greatly missed.
Received: 27 March 2002 / Published online: 8 May 2002 相似文献
9.
The perovskite structured material LaGaO3 doped with 10 mol-% strontium and 20 mol-% magnesium was prepared by two different wet-chemical synthesis routes. The total
conductivity was measured in air and under an oxygen partial pressure of 10−20 bar. There was a decrease by 10 % in 4 days when the atmosphere was changed from air to 10−20 bar. This process is reversible. Hebb-Wagner measurements resulted in values for the electronic minority charge carrier conductivities
in pure oxygen of log σh [S/cm]=−4.02 and log σe [S/cm]=−15.5 for the holes and electrons, respectively, at 600 °C. In the partial pressure range 10−3 bar≤p(O2)≤1 bar, a slope of +1/4 was observed for d(log (σh)) / d(log (p(O2)) at T=600, 650 and 700 °C. That is in agreement with the assumption of a large number of oxygen vacancies. The diffusion
coefficient of the holes was evaluated from the relaxation curves to be 1.1*10−7 cm2/s at 600 °C. Degradation effects were observed under highly reducing conditions which are attributed to the formation of
gallium-platinum alloys and the loss of gallium oxide if O2 is available in the gas phase.
Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999. 相似文献
10.
S.T. Sanders 《Applied physics. B, Lasers and optics》2002,75(6-7):799-802
A swept-wavelength source is created by connecting four elements in series: a femtosecond fiber laser at 1.56 μm, a non-linear
fiber, a dispersive fiber and a tunable spectral bandpass filter. The 1.56-μm pulses are converted to super-continuum (1.1–2.2 μm)
pulses by the non-linear fiber, and these broadband pulses are stretched and arranged into wavelength scans by the dispersive
fiber. The tunable bandpass filter is used to select a portion of the super-continuum as a scan-wavelength output. A variety
of scan characteristics are possible using this approach. As an example, an output with an effective linewidth of approximately
1 cm-1 is scanned from 1350–1550 nm every 20 ns. Compared to previous scanning benchmarks of approximately 1 nm/μs, such broad,
rapid scans offer new capabilities: a gas sensing application is demonstrated by monitoring absorption bands of H2O, CO2, C2H2 and C2H6O at a pressure of 10 bar.
Received: 5 August 2002 / Revised version: 23 September 2002 / Published online: 22 November 2002
RID="*"
ID="*"Corresponding author. Fax: +1-608/265-2316, E-mail: ssanders@engr.wisc.edu 相似文献
11.
J. Luque J.B. Jeffries G.P. Smith D.R. Crosley 《Applied physics. B, Lasers and optics》2001,73(7):731-738
The combination of two-dimensional, planar laser-induced fluorescence (PLIF) and cavity ring-down (CRD) absorption spectroscopy
is applied to map quantitatively the spatial distributions of CH2O and CH in a methane/air flame at 25 Torr. Both species are detected in the same spectral region using the overlapping CH2O A 1
A
2
-X
1
A
1
41
0 and CH B-X(1,0 )bands. The combination of diagnostic techniques exploits the spatial resolution of LIF and the quantitative
CRD absorption measure of column density. The spatially resolved PLIF provides the distribution of absorbers and line-of-sight
CRD absorption the absolute number density needed for quantitative concentration images. The peak CH2O concentration is (3.5±1.4 )×1014 cm-3, or 1450±550 ppm at 1000 K. The lack of precise absorption cross-section data produces these large error limits. Although
a flame model predicts lower amounts, these large uncertainties limit this measurement’susefulness as a test of the flame
chemistry.
Received: 24 April 2001 / Revised version: 10 July 2001 / Published online: 10 October 2001 相似文献
12.
4 /N2/O2 flame to spectral simulations based on a two-level theory for stationary, saturable absorbers by Abrams et al. Temperatures
determined from least-squares fits of simulations to experimental spectra in the A2Σ+?X2Π+(0,0) band are compared to temperatures obtained from OH absorption spectroscopy and a radiation-corrected thermocouple. We
find that DFWM rotational temperatures derived from Q-branch spectra agree with thermocouple and are independent of pump laser
intensity for low to moderate saturation (I≈Isat). However, the temperatures are systematically low and depend on pump intensity if the analysis neglects saturation effects.
We demonstrate a method for obtaining an effective pump saturation intensity for use with the two-level model. This approach
for analyzing saturated DFWM line intensities differs from previous work in that the use of the theory of Abrams et al. rather
than a transition-dipole-moment power law allows treatment of a much wider range of saturation. Based on the observed signal-to-noise
ratio an NO detection sensitivity of 25 ppm is projected, limited by a DFWM background interference specific to hydrocarbon
flames.
Received: 15 September 1998 / Revised version: 18 November 1998 / Published online: 24 February 1999 相似文献
13.
Potentiometric CO2 gas sensors with Li conducting glasses/glass ceramics of the system Li2O-Al2O3-SiO2 (different nominal composition) as solid electrolytes have been investigated. Li2CO3 was used as CO2 and O2 sensitive auxiliary electrode. During the sensor test measurements, the CO2 partial pressure was varied between 1×10−3 and 1×10−1 bar at a constant O2 partial pressure of 2.1×10−1 bar whereas N2 was used as carrier gas. Comparative measurements were accomplished with sensors comprising Na and K ion conducting glasses.
A metastable reference electrode was formed at the contact zone between the Au metal electrode and the former Li glasses of
definite nominal composition by crystallization processes taking place, which lead to stable, reproducible CO2 dependent EMF signals for more than 90d. The thermodynamically expected EMF difference and the observed EMF difference agree
quite well between 500 and 600 °C.
At 600 °C, the drift of sensors with glasses as solid electrolytes and direct Au glass/glass ceramics contact as reference
electrode amounts typically 0.32 mV/d (p(CO2)=1×10−3 bar, p(O2)=2.1×10−1 bar at the measuring electrode), if a metastable multiphase equilibrium is formed. At identical partial pressures of CO2 and O2, the signal reproducibility of these sensors with different solid electrolyte glasses of the same nominal composition lies
within 30 mV at 600 °C.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
14.
S. Böckle J. Kazenwadel T. Kunzelmann D.-I. Shin C. Schulz 《Applied physics. B, Lasers and optics》2000,70(5):733-735
Single-shot formaldehyde laser-induced fluorescence (LIF) imaging measurements in a technical scale turbulent flame have been
obtained using XeF excimer laser excitation in the ?1A2-˜X1A1 transition at 353.2 nm. Measurements have been carried out in a 150 kW natural gas swirl burner where formaldehyde distribution
fields have the potential, in combination with OH concentration fields, to visualize the heat release distribution and therefore
give an optimal visualization of flame-front positions. The extended areas where formaldehyde was detected in the swirl flame
indicates the presence of low temperature chemistry in preheated gas pockets before ignition.
Received: 31 January 2000 / Revised version: 2 March 2000 / Published online: 5 April 2000 相似文献
15.
A.T. Hartlieb D. Markus W. Kreutner K. Kohse-Höinghaus 《Applied physics. B, Lasers and optics》1997,65(1):81-91
2 Σ+) was measured in a low-pressure H2/O2 flame for three rotational levels of OH (v′=1). Rate coefficients for collisions with H2O and N2 were determined. At 1600 K, kVET (N2) is (in 10-11 cm3s-1) 10.1±2, 6.1±1.8, and 3.8±1.3 for N′=0, 5, and 13, respectively. The kVET (H2O) is <1.1±1.8. The kQ (N2) is <2.4±8 for both vibrational levels. The kQ (H2O) in v′=1 is 59.1±6.5, 54.7±6.4, and 54.9±6.6 for N′=0, 5, and 13, respectively, and, determined indirectly, 74.6±10.4, 70.6±10.3, and 63.4±7.3 for N′=0, 5, and 13 in v′=0. A multi-level model of OH population dynamics, which is being developed for the quantitative simulation of experimental
LIF spectra, was extended to include VET. It was attempted to simulate state-to-state-specific VET coefficients for N2 collisions. From these simulations it appears that angular momentum conservation does not determine the N dependence of the
vibrational relaxation step.
Received: 9 September 1996/Revised version: 6 January 1997 相似文献
16.
The use of mid-infrared polarization spectroscopy (PS) for the detection of CO2 has been demonstrated. The P(13) and P(14) resonances of the (0 00 0)→(1 00 1) transition of CO2 were probed using a single-mode optical parametric generator system to produce a high-intensity laser beam at approximately
2.7 μm. The experiments were performed in an atmospheric pressure CO2 jet and also in a sub-atmospheric pressure gas cell. The experimental results were compared with the results of the time-dependent
density-matrix equations using direct numerical integration. The Zeeman-state structure of the upper and lower energy levels
was included in the multi-state formulation of the density-matrix equations. Fifty-eight Zeeman states and two bath levels
were included in the numerical analysis of the P(14) transition. The measured and calculated PS line shapes were in good agreement,
and the absolute experimental signal level agreed with the theoretical calculation to within a factor of five.
Received: 20 March 2002 / Revised version: 16 August 2002 / Published online: 11 December 2002
RID="*"
ID="*"Present address: Innovative Scientific Solutions Inc., 2766 Indian Ripple Road, Dayton, OH 45 440, USA
RID="**"
ID="**"Corresponding author. Fax: +1-765/494-0539, E-mail: Lucht@purdue.edu
RID="***"
ID="***"Present address: School of Mechanical Engineering, Purdue University, W. Lafayette, IN 47807-2040 USA 相似文献
17.
Z. Liu X. Sun X. Zhou X. Lei Y. Guo Y. Zhang X. Chen H. Jin Y. Luo S.X. Wen C.X. Yang G.J. Yuan G.S. Li X.A. Liu W.D. Luo Y.S. Chen 《The European Physical Journal A - Hadrons and Nuclei》1998,1(2):125-135
High-spin states of 117Xe were investigated by means of in-beam γ-ray spectroscopic techniques via the reaction of 28Si bombarding a 92Mo target at beam energies of 100-120 MeV. A positive-parity rotational band decaying into the yrast negative-parity band
by a series of enhanced E1 transitions was observed for the first time, implying the existence of octupole correlations in
117Xe. The B(E1) values increase with spin. The νd5/2 band was firmly established up to 27/2+ and the B(M1)/B(E2) ratios were extracted from the relative intensities of γ-rays in this band. The previously known νh11/2 and νg7/2 [413]5/2+α=−1/2 bands were confirmed and extended up to high spins and two bandcrossings are observed in the latter at ħω=0.33 and
0.44 MeV, respectively. The bandcrossings and configurations of these bands are discussed by TRS and CSM calculations. In
a γ–γ–t measurement, the 11/2− and 7/2− levels were identified as two isomers with half-lives of 59.4±20 ns and 16.5±8.0 ns, respectively.
Received: 17 June 1997 / Revised version: 29 September 1997 相似文献
18.
C. S. Lee J. H. Ha J. H. Lee J. Y. Huh J. C. Kim C. -B. Moon S. J. Chae T. Komatsubara T. Shizuma H. Kimura K. Matsuura K. Kato Y. Sasaki H. Ishiyama K. Furuno 《The European Physical Journal A - Hadrons and Nuclei》2000,8(1):1-3
High-Spin states of odd-odd 166Lu were populated using the 139La(30Si,3nγ)166Lu at a beam energy of 120 MeV. Twelve new γ-rays were placed on top of the previously known two rotational bands built upon πg
7/2⊗νi
13/2 and πh
11/2⊗νi
13/2. Extending high-spin states up to 21+ and 25− for each band, we have observed the onset of band crossing near ħω
c ≈ 0.35 MeV. The band crossing frequency of the yrast πh
11/2⊗νi
13/2 band is consistent with the neutron BC band crossing observed in lighter odd-odd Lu isotopes. 相似文献
19.
W. Urban J.A. Pinston T. Rzaca-Urban A. Złomaniec G. Simpson J.L. Durell W.R. Phillips A.G. Smith B.J. Varley I. Ahmad N. Schulz 《The European Physical Journal A - Hadrons and Nuclei》2003,16(1):11-15
A new band, populated by the spontaneous fission of 248Cm and studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array, was observed in 99Zr. The 1038.8 keV band head with a half-life T
1/2 = 54(10) ns is interpreted as a K-isomer, corresponding to the 9/2[404] neutron-hole excitation. It is the first observation of this orbital in the mass A ∼ 100 region. The quadrupole moment, Q
0 = 3.9(3) eb deduced for the new band indicates a large deformation of β = 0.41, which is produced by a specific shape-coexistence
mechanism, known in other regions and now found in the A ∼ 100 nuclei.
Received: 11 September 2002 / Accepted: 31 October 2002 / Published online: 17 January 2003
RID="a"
ID="a"e-mail: urban@fuw.edu.pl
Communicated by D. Schwalm 相似文献
20.
Crystalline structure and optical spectroscopy of Er3+-doped KGd(WO4)2 single crystals 总被引:2,自引:0,他引:2
M.C. Pujol M. Rico C. Zaldo R. Solé V. Nikolov X. Solans M. Aguiló F. Díaz 《Applied physics. B, Lasers and optics》1999,68(2):187-197
4 )2 single crystals doped with Er3+ have been grown by the flux top-seeded-solution growth method. The crystallographic structure of the lattice has been refined,
being the lattice constants a=10.652(4), b=10.374(6), c=7.582(2) Å, β=130.80(2)°. The refractive index dispersion of the host
has been measured in the 350–1500 nm range. The optical absorption and photoluminescence properties of Er3+ have been characterised in the 5–300 K temperature range. At 5 K, the absorption and emission bands show the (2J+1)/2 multiplet
splittings expected for the C2 symmetry site of Er in the Gd site. The energy positions and halfwidths of the 72 sublevels observed have been tabulated
as well as the cross sections of the different multiplets. Six emission band sets have been observed under excitation of the
4F7/2 multiplet. The Judd–Ofelt (JO) parameters of Er3+ in KGW have been calculated: Ω2=8.90×10-20 cm2, Ω4=0.96×10-20 cm2, Ω6=0.82×10-20 cm2. Lifetimes of the 4S3/2, 4F9/2, and 4I11/2 multiplets have been measured in the 5–300 K range of temperature and compared with those calculated from the JO theory.
A reduction of the 4S3/2 and 4I11/2 measured lifetimes with increasing erbium concentration has been observed, moreover the presence of multiphonon non-radiative
processes is inferred from the temperature dependence of the lifetimes.
Received: 15 December 1997/Revised version: 10 July 1998 相似文献