Diode laser atomic fluorescence temperature measurements in low-pressure flames

Temperature measurements have been performed in a low-pressure flame by the technique of diode laser induced atomic fluorescence. The experiments were done in a near-stoichiometric flat-flame of premixed methane, oxygen and nitrogen, at a pressure of 5.3 kPa. Indium atoms were seeded to the flame and probed using blue diode lasers; the lineshapes of the resulting fluorescence spectra were used to determine the flame temperature at a range of heights above the burner plate. The particular issues associated with the implementation of this measurement approach at low pressure are discussed, and it is shown to work especially well under these conditions. The atomic fluorescence lineshape thermometry technique is quicker to perform and requires less elaborate equipment than other methods that have previously been implemented in low-pressure flames, including OH-LIF and NO-LIF. There was sufficient indium present to perform measurements at all locations in the flame, including in the pre-heat zone close to the burner plate. Two sets of temperature measurements have been independently performed by using two different diode lasers to probe two separate transitions in atomic indium. The good agreement between the two sets of data provides a validation of the technique. By comparing thermocouple profiles recorded with and without seeding of the flame, we demonstrate that any influence of seeding on the flame temperature is negligible. The overall uncertainty of the measurements reported here is estimated to be ±2.5% in the burnt gas region.     

Measurement of temperature, fuel concentration and equivalence ratio fields using tracer LIF in IC engine combustion

A technique based on planar laser-induced fluorescence of 3-pentanone, for measurements of absolute concentration, temperature and fuel/air equivalence ratios in turbulent, high-pressure combustion systems such as an internal combustion engine is presented. Quasi-simultaneous excitation with 248 nm and 308 nm of 3-pentanone that is used as a fluorescence tracer doped to iso-octane, yields pairs of strongly temperature-dependent fluorescence images. Previous investigations have resulted in information on temperature and pressure dependence of absorption cross-sections and fluorescence quantum yields. Using these data the ratio of corresponding fluorescence images can be converted to temperature images. Instantaneous temperature distribution fields in the compression stroke and in the unburned end-gas of an SI engine were measured. The temperature fields obtained from the two-line technique are used to correct the original tracer-LIF images in order to evaluate quantitative fuel distributions in terms of number densities and fuel/air equivalence ratio. Received: 10 March 2000 / Revised version: 19 April 2000 / Published online: 16 August 2000     

Two-dimensional atomic hydrogen concentration maps in hot-filament diamond-deposition environment

This paper reports the two-dimensional mapping of atomic hydrogen concentration with two-photon excited laser induced fluorescence in a multi-wire grid hot-filament chemical vapor deposition reactor. The measurements were made in a diamond film deposition environment under different filament temperatures and wire configurations. The measurement was calibrated with a titration reaction using NO₂ as a titrant. The kinetic gas temperature in the reactor was measured from the Doppler broadening of the Lyman-β transition excited in the fluorescence. The filament temperature was found to have a significant effect on atomic hydrogen production and transfer to the substrate. The axial concentration distributions were compared to a one-dimensional kinetic gas–surface chemistry model with good agreement. The model produced a reasonable estimate for the bulk diamond film growth rate. Received: 25 June 2001 / Revised version: 15 February 2002 / Published online: 2 May 2002     

用激光感生荧光法测量亚稳态原子寿命

本文用激光感生荧光法(LIF)分析了Gd原子亚稳态能级215cm~(-1),533cm~(-1),999cm~(-1)在原子束中的速度分布。由原子束轴线上两不同点上的亚稳态原子速度分布的变化得到了亚稳态原子的寿命。理论分析和实验结果表明这是一种简单、灵敏并且有效的亚稳态原子寿命测量方法。     

Nonlinear optical techniques for plasma diagnostics

The application of various nonlinear optical laser spectroscopic techniques to plasma diagnostics are reported. The techniques discussed in this paper are two-photon laser induced fluorescence spectroscopy, double-resonant four-wave mixing, coherent anti-Stokes Raman-scattering (CARS), and a combination of emission spectroscopy and CARS. They are applied to measurements of atomic hydrogen densities, molecular temperature, chemical composition, electric field distributions, and vibrational population distribution. The basic principles are described and important aspects of the methods are discussed in context with application to various kinds of discharges at low and elevated pressures     

A thermometry technique based on atomic lineshapes using diode laser LIF in flames

We report on the development of a novel diode laser thermometry technique permitting temperature measurements in flames based on the fluorescence lineshapes of an atomic tracer species. The technique, which we term OLAF (one-line atomic fluorescence) requires only a single diode laser source for excitation, is simple to implement, and has excellent spatial resolution. Temperatures are deduced from the 5²P_1/2 → 6²S_1/2 transition of atomic indium, the lineshape of which is highly sensitive to temperature changes at typical flame conditions. A rigorous validation is performed in a reference flame with comparisons to measurements by CARS and by Na-line reversal, and to numerical simulations.     

Optimized temperature measurement with time-of-flight method

Driven by resonance probe light background Rubidium gas can emit fluorescence, which interacts with the falling atomic cloud in the temperature measurement with the time-of-flight (TOF) method and influence the experimental results. The dependencies of the acceleration and the temperature of the atomic cloud on the detuning of the probe beams were studied. We propose that the deviation of the acceleration from the gravity acceleration can be taken as a criterion of the accuracy of the temperature measurement using TOF method. Moreover, using the principle of the radiation force on the cold atomic cloud, one may measure the considerably weak intensity of the fluorescence.     

An investigation of the photothermal deflection spectroscopy technique for temperature measurements in a flame

The technique of photothermal deflection spectroscopy (PTDS) is investigated for temperature measurements in a flame. The spatial distribution of temperature is measured in two different types of burners operating with methane and oxygen, and methane and air. The spatial distributions of the temperature are in qualitative agreement with our expectations. At two points, the temperatures measured by PTDS have been compared with those measured by Boltzmann distributions. The measurements agree within their uncertainties. All the effects that affect the reliability of this technique are investigated and discussed. Finally, the pros and cons of the PTDS technique for temperature measurement are discussed. Received: 31 January 2002 / Published online: 8 August 2002     

Two-line atomic fluorescence as a temperature probe for highly sooting flames

We investigate the applicability of two-line atomic fluorescence (TLAF) from seeded indium atoms for temperature measurements in highly sooting flames. The results show that TLAF holds promise for two-dimensional temperature measurements in sooting and fuel-rich flames under conditions in which other thermometry techniques fail, a result that is attributed to the superior characteristics of the indium atomization process. Furthermore, no native species was found to interfere spectrally with the detected TLAF wavelengths. Advantages of and problems with the technique are discussed.     

Atomic probes of electromagnetic and weak interactions with trapped radioactive atoms

The alkali element francium has a simple electronic structure, and copious amounts of a wide range of isotopes can be produced in present and future rare isotope facilities. The atomic parity violating weak interaction in Fr is 18 times larger than in Cs, which makes it one of the best candidates to search for the effects of the weak interaction and its isotopic dependence. Atomic trapping methods now offer new ways to study these atoms with precision, and we will discuss some of our recent measurements with trapped Fr atoms. Future measurements of the spin-independent weak interaction can be used to test the standard model, but advances in atomic theory and improved understanding of the neutron distribution in nuclei are needed to make progress. We have made precise hyperfine-anomaly measurements in Fr and have shown that they are sensitive to the radial distribution of the neutron magnetization. Measurements of this type can help to constrain the neutron distributions. Future measurements of the spin-dependent weak interaction should allow extraction of the nuclear anapole moments for a sequence of isotopes, and allow separation of the neutron and proton weak interactions between hadrons. Received: 1 May 2001 / Accepted: 4 December 2001     

Two-line planar fluorescence for temporally resolved temperature imaging in a reacting supersonic flow over a body

An instantaneous temperature imaging technique for chemically reacting, supersonic flows over bodies is described and demonstrated in a H₂/O₂/Ar shock tube flow (M=1.3, 0.7 atm, 1760K freestream). Based on a planar fluorescence measurement, the approach uses a two-line rotational population ratio to infer temperature. The measured 2-d temperature profiles qualitatively match the expected flowfield structure around the blunt body, and the temperature increase across the bow shock in a single-shot measurement agrees within 5–10% of the prediction of a 1-d shock analysis. The significant systematic error sources for the technique are detailed, and the random error effects associated with shot-noise-limited fluorescence images are statistically analyzed to identify transitions which minimize the temperature errors for instantaneous and average measurements. Even for average temperature measurements, the analysis predicts errors which can be as large as 5–10% when noisy fluorescence images are used in conjunction with low temperature sensitivity. In general, temperature errors can be reduced by increasing sensitivity, i.e., the energy separation of the two rotational levels, until the fluorescence shot-noise rises to a value of 30–50% within the temperature range of interest.     

Quantum nondemolition measurement of transverse atomic position in Kapitza-Dirac atomic beam scattering

It is demonstrated that one can measure the distribution of the transverse position of an atom crossing one or more optical cavities by monitoring the phase of the standing wave fields in the cavities. For the atom-field interaction the Kapitza-Dirac regime is assumed; it is shown that in this regime the method represents a quantum nondemolition measurement of the atomic position. On the other hand it can be applied to prepare narrow distributions of the transverse atomic position. In order to show this, a numerical simulation is performed, which illustrates the collapse of a broad initial Gaussian wavepacket, which can be coherent or incoherent, to a distribution with narrow peaks. Preparing the cavity fields in a squeezed state, one can greatly enhance the impact of the cavity field measurements on the atomic density matrix.     

Monte Carlo studies of the resonance fluorescence technique for atmospheric atomic oxygen measurements

The resonance fluorescence of the O (³P³S) triplet has been used extensively for rocket-borne measurements of atomic oxygen in the mesosphere and lower thermosphere. The accuracy and compatibility of different experimental configurations are however still a subject of controversy. In order to better quantify the measurements, we have developed a 3-dimensional Monte Carlo model which simulates the radiative transfer inherent to atom detection by means of resonance lamps. Angle-dependent partial frequency redistribution describes the fluorescence process, natural broadening becoming significant when the line center optical thickness exceeds 10. Applying the model to a recently flown rocket instrument, a strong temperature dependence and nonlinear relations between atomic oxygen abundance and fluorescence signal are found at densities above 5.10¹⁰ cm⁻³. Above 1.10¹² cm⁻³, the signal gradually saturates and useful measurements cannot be obtained. The spatial distribution of the scattering events and effects of the payload motion are analyzed. A discussion of the results is applied to different calibration techniques for rocket instruments.     

Lifetimes and oscillator strengths of neutral vanadium

Oscillator strengths of 105 V(I) lines in the spectral range 2800–6000 Å were obtained by lifetime, emission, and hook measurements. Relative sets of ?-values were determined by combining emission measurements on a hollow cathode with hook measurements in a high temperature furnace, whereby no assumption concerning the plasma state is used and no temperature determination is required. The determination of the radiative lifetimes was performed by selective laser excitation of an atomic beam of vanadium and time-resolved observation of the reemitted fluorescence after the pulse. The absolute ?-values have an uncertainty of 12% on average. Both for the lifetimes and the ?-values a comparison with literature data is performed.     

Resonance fluorescence and quantum jumps in single atoms: Testing the randomness of quantum mechanics

When a single trapped ¹⁹⁸Hg⁺ ion is illuminated by two lasers, each tuned to an appropriate transition, the resulting resonance fluorescence switches on and off in a series of pulses resembling a bistable telegraph. This intermittent fluorescence can also be obtained by optical pumping with a single laser. Quantum jumps between successive atomic levels may be traced directly with multiple-resonance fluorescence. Atomic transition rates and photon antibunching distributions can be inferred from the pulse statistics and compared with quantum theory. Stochastic tests also indicate that the quantum telegraphs are good random number generators. During periods when the fluorescence is switched off, the radiationless atomic currents that generate the telegraph signals can be adjusted by varying the laser illumination: if this coherent evolution of the wave functions is sustained over sufficiently long time intervals, novel interactive precision measurements, near the limits of the time-energy uncertainty relations, are possible.     

Comparison of Detection Limits in Atomic Fluorescence and Absorption Spectroscopy

Dagnall, Taylor, and West have recently compared detection limits for a number of metals in atomic fluorescence and absorption spectroscopy and have concluded that “atomic fluorescence measurements using an electrodeless discharge tube are inherently more sensitive than those obtainable by atomic absorption measurements”. Likewise West and Williams have compared the two techniques for magnesium²and silver³, using high-intensity hollow-cathode lamps as sources, and have found much lower detection limits in fluorescence than in absorption.     

Zur Statistik der atomteilcheninduzierten Elektronenauslösung aus Festkörpern

In this paper measured probability distributions of the electron ejection from solids due to bombardment by atomic particles with kinetic energy are compared with theoretical distributions. With regard to the applied measuring parameters, it is shown that best adaption is obtainable by use of one of the suggested theoretical distributions respectively. A heuristic foundation is given for this fact, and the assumption is confirmed that careful measurements of the probability distributions are additional sources of information with regard to the investigation of the atomic particle-induced electron ejection.     

Spectroscopic and lasing characterisation of a dicarbazovinylene-MEH-benzene dye

The dye 1,4-bis(9-ethyl-3-carbazovinylene)-2-methoxy-5-(2′-ethyl-hexyloxy)-benzene (abbreviated 2CzV-MEH-B) dissolved in tetrahydrofuran (THF) and as neat film is characterised by optical absorption and emission spectroscopy. The absorption and stimulated emission cross-section spectra, the fluorescence quantum distributions, fluorescence quantum yields, degrees of fluorescence polarisation, and fluorescence lifetimes are determined. A lasing characterisation is carried out by pumping with single second harmonic pulses of a mode-locked ruby laser (wavelength 347.15 nm, pulse duration 35 ps). The excited-state absorption at the pump laser wavelength is determined by saturable absorption measurements. Laser oscillation of the dye in THF in a rectangular cell is achieved by transverse pumping using the uncoated cell windows for light feedback. From the emission behaviour around threshold the excited-state absorption cross-section spectrum in the laser active spectral region is extracted. The wave-guided travelling-wave lasing behaviour of the dye as neat film is studied by analysis of the amplification of the transverse pumped spontaneous emission. Surface emitting distributed-feedback lasing was achieved with a neat film on corrugated second-order periodic gratings.     

Investigation of partial sputtering of lithium from a binary Al/Li alloy with laser induced fluorescence

Sputtering investigations of an Al/Li alloy containing 9.1 at-% of lithium have been performed for 6 keV helium ion bombardment. Absolute particle densities and velocity distributions of the sputtered neutral lithium atoms were measured with laserinduced fluorescence. The amount of sputtered lithium was found to be constant for target temperatures ranging from room temperature up to 500° C. The mean transport velocity and the sputtering yield of the Li component have been calculated from the measurements. Thermal evaporation of neutral Li atoms could be measured independently of the presence of the helium beam for target temperatures above 300° C. The experimental results indicate that the surface is covered by lithium with at least several atomic layers even under highcurrent ion irradiation.Preliminary results have been presented at the SYMPOSIUM ON SPUTTERING, Spitz/Austria (1986)     

Single molecule acid-base kinetics and thermodynamics

We report a method in which temperature dependent single-molecule fluorescence measurements are used to study the kinetics and thermodynamics of the acid-base interaction in films of photoresist polymer. We use the two distinct fluorescent prototropic forms of Coumarin 6 (C6-->C6+) to indicate the state of the acid-base system. Data are analyzed using a statistical model of the intensity probability distributions, yielding temperature dependent proton exchange rates, which is confirmed through agreement with a simple two-state Monte Carlo model. The temperature dependent rates are used to calculate the activation enthalpy for proton exchange.