| 1. |
- Hellström, Jonas, et al.
(author)
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Efficient Yb : KGW lasers end-pumped by high-power diode bars
- 2006
-
In: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 82:2, s. 235-239
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Journal article (peer-reviewed)abstract
- The laser performance of Yb:KGW under end-pumping with high-power diode bars has been investigated. In one configuration, the pump is delivered through an optical fiber yielding a symmetric but unpolarized pump spot. In the second configuration, the pump is delivered through an optical lens system yielding a polarized but asymmetric pump spot. Both configurations resulted in a maximum optical to optical efficiency of 47% and a maximum power of 12.4 W has been generated with the fiber coupled pump source. The output power was limited by crystal fracture, which occurred at an estimated temperature gradient of 1.2 x 10(5) K/m. Thermal lensing and laser tuning characteristics are also investigated.
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| 2. |
- Abou Nada, Fahd Jouda, et al.
(author)
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Improved measurement precision in decay time‑based phosphor thermometry
- 2016
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 1432-0649 .- 0946-2171. ; 122
-
Journal article (peer-reviewed)abstract
- This study comprises a continuation of the previous efforts of the authors to characterize different sources of errors in phosphor thermometry based on the determination of luminescence decays from thermographic phosphors. Whereas earlier investigations focused on point detectors utilizing different sensor technology, this work presents a comparison of four PMTs that are identical in terms of their product type. These detectors are supposedly identical, but the investigations revealed that their response is strictly individual. This study also shows a linear excitation energy dependence for the decay time of cadmium tungstate (CdWO4), the phosphor being used in this work. In addition, the potential influence of the intense and short fluorescence peak preceding the weaker and longer exponential decay in some phosphor materials, was investigated using the electrical signal gating capability of the PMT. Finally, the evaluated decay time also appeared to be affected by the oscilloscope settings used when recording the phosphorescence signals. The presented results indicate that all operating parameters from the calibration measurement need to be rigorously reproduced in order to avoid systematic temperature errors in phosphor thermometry experiments that are based on reproducible measurements of the decay time. These results should be of more general interest also outside the phosphor community as the findings, presented herein, in principal concern all kinds of measurements that are dependent on reproducible measurements of signal shapes or time-transients.
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| 3. |
- Afzelius, Mikael, et al.
(author)
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Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. I. Inter-branch interference effect
- 2002
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 75:6-7, s. 763-769
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Journal article (peer-reviewed)abstract
- An improved model for pure rotational coherent anti-Stokes Raman scattering (CARS) has been developed or the dual-broadband approach. This model takes into account the fact that coherent anti-Stokes as well as Stokes radiation are generated simultaneously, and these two branches overlap and interact at high pressures giving rise to an inter-branch interference effect. In combustion studies, the anti-Stokes branch is used to determine temperature and concentrations of key species, of which nitrogen is the most widely used, and we have found that the interference effect on the anti-Stokes side is of such magnitude that it clearly needs to be taken into account at pressures of a few MPa. The necessary modifications to the total third-order susceptibility are presented and a derivation of the convolution integral for a finite-bandwidth pump source is given.
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| 4. |
- Afzelius, Mikael, et al.
(author)
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Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. II. Rotational Raman line widths
- 2002
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 75:6-7, s. 771-778
-
Journal article (peer-reviewed)abstract
- Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic technique for thermometry at pre-combustion temperatures an atmospheric pressure. However, at pressures of several MPa, a previous investigation revealed large discrepancies between experimental data and the theoretical model. A re-evaluation has been made of these data (at room temperature and in the range 1.5-9 MPa) with two improvements to the spectral code. The first is the inclusion of an inter-branch interference effect, which is described in detail in Paper I. The second is the use of experimental S-1-branch Raman line widths measured at 295 K, with a temperature dependence extracted from semi-classical calculations following the Robert-Bonamy formalism. It is shown that these two modifications significantly improve the theoretical model, since both the spectral fits and the accuracy of the evaluated temperatures are considerably improved.
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| 5. |
- Aldén, Marcus, et al.
(author)
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Applications of two-photon absorption for detection of CO in combustion gases
- 1984
-
In: Applied Physics B. - 0946-2171. ; 33:4, s. 205-208
-
Journal article (peer-reviewed)abstract
- Laser-induced fluorescence has been used for detection of CO in different environments. The fluorescence light was obtained by using a two-photon transition between theX1?- and theB1?- electronical states around 230 nm. Cell measurements indicate a detection limit lower than 0.1 ppm. Measurements in a CH4/air flame and in a low pressure dc discharge were realized with a diode-array detector, which was used in an imaging mode, permitting single-shot CO distributions to be captured.
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| 6. |
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| 7. |
- Alnis, Janis, et al.
(author)
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Laser spectroscopy of free molecular oxygen dispersed in wood materials
- 2003
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 77:6-7, s. 691-695
-
Journal article (peer-reviewed)abstract
- The recently introduced Gas in Scattering Media Absorption Spectroscopy (GASMAS) technique is applied to the study of various wood samples. Molecular oxygen in the pores of the strongly scattering material is detected using diode laser spectroscopy around 760 nm. Diffuse light propagation in these media is studied by time-dispersion measurements. Furthermore, anisotropy related to the fibre structure of wood and gas diffusion properties are studied. Promising extensions of the experiments are discussed.
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| 8. |
- Alonso, Benjamin, et al.
(author)
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Characterization of sub-two-cycle pulses from a hollow-core fiber compressor in the spatiotemporal and spatiospectral domains
- 2013
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 112:1, s. 105-114
-
Journal article (peer-reviewed)abstract
- We have post-compressed 25 fs (Fourier limit) amplified pulses in an argon-filled hollow-core fiber. The output pulses were compressed using a pair of wedges and chirped mirrors down to 4.5 fs (Fourier limit of 4.1 fs), which corresponds to less than two optical cycles. We then performed the characterization of the pulses by combining the d-scan and the STARFISH techniques. The temporal (and spectral) measurement of the pulses is done with d-scan, which is used as the reference to extend the characterization to the spatiotemporal (and spatiospectral) amplitude and phase of the pulses by means of STARFISH. The post-compressed pulses at the output of the hollow-fiber had an energy of 150 mu J. The analysis of the pulses revealed larger spectral broadening and blue-shift, and shorter duration at the center of the beam. For the first time, we demonstrate the complete characterization of intense ultra-broadband pulses in the sub-two-cycle regime, which provides an improved insight into the properties (space-time and space-frequency) of the pulses and is highly relevant for their applications.
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| 9. |
- Aurand, Bastian, et al.
(author)
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Reduction of X-ray generation in high-intensity laser ion acceleration
- 2015
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 118:2, s. 247-251
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Journal article (peer-reviewed)abstract
- In this paper, we report on measurements of bremsstrahlung in laser ion acceleration experiments from ultra-thin, polymer-based target foils. The influence of laser polarization on the generated radiation, the maximum achievable proton energy and the total proton number is investigated. A clear benefit in terms of radiation reduction by the use of circular polarized light can be observed. At the same time, the total number of accelerated protons was increased.
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| 10. |
- Axelsson, Boman, et al.
(author)
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Laser-induced incandescence for soot particle size and volume fraction measurements using on-line extinction calibration
- 2001
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 72:3, s. 367-372
-
Journal article (peer-reviewed)abstract
- A novel technique for two-dimensional measurements of soot volume fraction and particle size has been developed. It is based on a combined measurement of extinction and laser-induced incandescence using Nd:YAG laser wavelengths of 532 nm and 1064 nm. A low-energy laser pulse at 532 nm was used for extinction measurements and was followed by a more intense pulse at 1064 nm, delayed by 15 ns, for LII measurements. The 532-nm beam was split into a signal beam passing the flame and a reference beam, both of which were directed to a dye cell. The resulting fluorescence signals, from which the extinction was deduced, together with the LII signal, were registered on a single CCD detector. Thus the two-dimensional LII image could be converted to a soot volume fraction map through a calibration procedure during the same laser shot. The soot particle sizes were evaluated from the ratio of the temporal LII signals at two gate time positions. The uncertainty in the particle sizing arose mainly from the low signal for small particles at long gate times and the uncertainty in the flame temperature. The technique was applied to a well-characterized premixed flat flame, the soot properties of which had been previously thoroughly investigated.
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| 11. |
- Badiei, Shahriar, 1969, et al.
(author)
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The Rydberg matter laser: excitation, delays and mode effects in the laser cavity medium
- 2005
-
In: Applied Physics B-Lasers and Optics. - : Springer Science and Business Media LLC. ; 81:4, s. 549-559
-
Journal article (peer-reviewed)abstract
- Temporal and temperature effects are studied in Rydberg matter (RM) formed from K atoms and N-2 molecules as the active medium in a cavity. The function of this setup as a laser was recently described. Temperature-variation studies show that the photons re-exciting the RM clusters usually have a longer wavelength than the photons emitted in the stimulated emission process in the cavity. The deficit is probably covered by background photons. Very long time constants observed after emitter temperature changes indicate that long-wavelength photon energy is accumulated in the RM clusters. Long-wavelength modes are located farther from the RM emitter. The modal structure can be TEM01 or TEM00, as observed clearly by the spatial structure in rapid pulsing experiments. The in-cavity chopped beam signal is delayed by approximately 50 mu s. The initial growth rate of the signal during chopping is temperature dependent. Tailing is also observed by chopping, but rapid pulsing of the beam with a spinning mirror does not show any delay of the start of the lasing. The conclusion is that delays exist in the stimulated emission process. The broad intense band appearing at 11 000 nm is shown to be formed partly by light in the range 3500-5000 nm, probably by standing wave interaction at the grating surface (grating bands).
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| 12. |
- Balcou, P, et al.
(author)
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High-order-harmonic generation: towards laser-induced phase-matching control and relativistic effects
- 2002
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 74:6, s. 509-515
-
Journal article (peer-reviewed)abstract
- We present a review of some recent results on high-order-harmonic generation, aiming at optimizing the photon flux to allow for future applications in extreme-ultra-violet non-linear optics. We first present new schemes to control phase matching of high harmonics in gases, by using the effect of the spatially varying atomic phase displayed by the high harmonics. An enhancement by a factor of 50 is observed in neon in conditions for which the gradient of the atomic dispersion balances the electronic dispersion. A new scheme to manipulate the laser field was demonstrated, and shown to improve phase matching. We then turn to high-harmonic generation by solid targets, and show that high harmonics generated by an intense 30-fs laser pulse remain collimated even at the threshold of the relativistic regime.
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| 13. |
- Bengtsson, P. E., et al.
(author)
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Soot-visualization strategies using laser techniques - Laser-induced fluorescence in C2 from laser-vaporized soot and laser-induced soot incandescence
- 1995
-
In: Applied Physics B. - 0946-2171. ; 60:1, s. 51-59
-
Journal article (peer-reviewed)abstract
- Strategies for spatially resolved soot volume-fraction measurements have been investigated in sooting laboratory flames with known soot characteristics. Two techniques were compared: Laser-Induced Fluorescence in C2 from Laser-Vaporized Soot (LIF(C2)LVS), and Laser-Induced Incandescence of soot (LII). The LII signal is the increased temperature radiation from soot particles which have been heated to temperatures of several thousand degrees as a consequence of absorption of laser radiation. The LIF(C2)LVS technique is based on the production of C2 radicals from laser-vaporized soot which occurs for laser intensities ≥107 W/cm2. A laser wavelength is chosen such that besides vaporizizng the soot, it also excites the C2 radicals, and the subsequent C2 fluorescence signal is detected. The signals from both techniques showed good correlation with soot volume fractions in the studied flame. The dependence of the signals on experimental parameters was studied, and the influence of interfering radiation, such as background flame luminosity and fluorescence from polyaromatic hydrocarbons, on studied signals was established. The potential of the two techniques for imaging of soot volume fractions in laboratory flames was demonstrated. Advantages and disadvantages of the studied techniques are discussed.
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| 14. |
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| 15. |
- Berrocal, Edouard, et al.
(author)
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Quantitative imaging of a non-combusting diesel spray using structured laser illumination planar imaging
- 2012
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 109:4, s. 683-694
-
Journal article (peer-reviewed)abstract
- Due to its transient nature, high atomization process, and rapid generation of fine evaporating droplets, diesel sprays have been, and still remain, one of the most challenging sprays to be fully analyzed and understood by means of non-intrusive diagnostics. The main limitation of laser techniques for quantitative measurements of diesel sprays concerns the detection of the multiple light scattering resulting from the high optical density of such a scattering medium. A second limitation is the extinction of the incident laser radiation as it crosses the spray, as well as the attenuation of the signal which is to be detected. All these issues have strongly motivated, during the past decade, the use of X-ray instead of visible light for dense spray diagnostics. However, we demonstrate in this paper that based on an affordable Nd:YAG laser system, structured laser illumination planar imaging (SLIPI) can provide accurate quantitative description of a non-reacting diesel spray injected at 1,100 bar within a room temperature vessel pressurized at 18.6 bar. The technique is used at lambda = 355 nm excitation wavelength with 1.0 mol% TMPD dye concentration, for simultaneous LIF/Mie imaging. Furthermore, a novel dual-SLIPI configuration is tested with Mie scattering detection only. The results confirm that a mapping of both the droplet Sauter mean diameter and extinction coefficient can be obtained by such complementary approaches. These new insights are provided in this article at late times after injection start. It is demonstrated that the application of SLIPI to diesel sprays provides valuable quantitative information which was not previously accessible.
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| 16. |
- Bjurshagen, Stefan, et al.
(author)
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Efficient generation of blue light by frequency doubling of a Nd:YAG laser operating on 4F3/2 → 4I9/2 transitions
- 2003
-
In: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 76:2, s. 135-141
-
Journal article (peer-reviewed)abstract
- Efficient room-temperature operation of F-4(3/2) --> I-4(9/2) transitions in diode-end-pumped Nd:YAG lasers at 946 nm and 938.5 nm is reported. 7.0-W continuous-wave output power at 946 nm and 3.9 W at 93 8.5 nm have been obtained. An analytical model has been developed for the quasi-three-level laser including the influence of energy-transfer upconversion. Frequency doubling of these transitions in periodically poled KTP generated blue light at 473 nm and 469 nm. Both single-pass extra-cavity as well as intracavity schemes have been investigated.
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| 17. |
- Bladh, Henrik, et al.
(author)
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Characteristics of laser-induced incandescence from soot in studies of a time-dependent heat- and mass-transfer model
- 2004
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 78:2, s. 241-248
-
Journal article (peer-reviewed)abstract
- The temporal behavior of the laser-induced incandescence (LII) signal is often used for soot-particle sizing, which is possible because the cooling behavior of a laser-heated particle is dependent on the particle size. The heat- and mass-transfer model describing the temporal LII-signal behavior has in this work been extended to include the influence of the primary particle-size distribution and the spatial distribution of laser energy. When evaluating primary particle size, a monodisperse size distribution is often assumed, although it is well known that a polydisperse distribution is a better description of the real situation. In this work the impact of this assumption is investigated for Gaussian and lognormal size distributions of different widths, and the result is a significant bias towards larger particle sizes because of the higher influence of larger particles on the LII signal. Moreover, the dependence of the LII signal on the laser fluence is studied for different spatial distributions of the laser energy. The top-hat, Gaussian sheet and Gaussian beam distributions were tested and it is established that the LII signal is strongly dependent on the choice of distribution. However, in this case the influence of particle size is minor.
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| 18. |
- Bladh, Henrik, et al.
(author)
-
Experimental and theoretical comparison of spatially resolved laser-induced incandescence (LII) signals of soot in backward and right-angle configuration
- 2006
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 83:3, s. 423-433
-
Journal article (peer-reviewed)abstract
- In-situ measurements of soot volume fraction in the exhausts of jet engines can be carried out using the laser-induced incandescence (LII) technique in backward configuration, in which the signal is detected in the opposite direction of the laser beam propagation. In order to improve backward LII for quantitative measurements, we have in this work made a detailed experimental and theoretical investigation in which backward LII has been compared with the more commonly used right-angle LII technique. Both configurations were used in simultaneous visualization experiments at various pulse energies and gate timings in a stabilized methane diffusion flame. The spatial near-Gaussian laser energy distribution was monitored on-line as well as the time-resolved LII signal. A heat and mass transfer model for soot particles exposed to laser radiation was used to theoretically predict both the temporal and spatial LII signals. Comparison between experimental and theoretical LII signals indicates similar general behaviour, for example the broadening of the spatial LII distribution and the hole-burning effect at centre of the beam due to sublimation for increasing laser pulse energies. However, our comparison also indicates that the current heat and mass transfer model overpredicts signal intensities at higher fluence, and possible reasons for this behaviour are discussed.
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| 19. |
- Bladh, Henrik, et al.
(author)
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Influence of Soot Particle Aggregation on Time-Resolved Laser-Induced Incandescence Signals
- 2011
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 104:2, s. 331-341
-
Journal article (peer-reviewed)abstract
- Laser-induced incandescence (LII) is a versatile technique for quantitative soot measurements in flames and exhausts. When used for particle sizing, the time-resolved signals are analysed as these will show a decay rate dependent on the soot particle size. Such an analysis has traditionally been based on the assumption of isolated primary particles. However, soot particles in flames and exhausts are usually aggregated, which implies loss of surface area, less heat conduction and hence errors in estimated particle sizes. In this work we present an experimental investigation aiming to quantify this effect. A soot generator, based on a propane diffusion flame, was used to produce a stable soot stream and the soot was characterised by transmission electron microscopy (TEM), a scanning mobility particle sizer (SMPS) and an aerosol particle mass analyzer coupled in series after a differential mobility analyzer (DMA-APM). Despite nearly identical primary particle size distributions for three selected operating conditions, LII measurements resulted in signal decays with significant differences in decay rate. However, the three cases were found to have quite different levels of aggregation as shown both in TEM images and mobility size distributions, and the results agree qualitatively with the expected effect of diminished heat conduction from aggregated particles resulting in longer LII signal decays. In an attempt to explain the differences quantitatively, the LII signal dependence on aggregation was modelled using a heat and mass transfer model for LII given the primary particle and aggregate size distribution data as input. Quantitative agreement was not reached and reasons for this discrepancy are discussed.
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| 20. |
- Bladh, Henrik, et al.
(author)
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Influence of spatial laser energy distribution on evaluated soot particle sizes using two-colour laser-induced incandescence in a flat premixed ethylene/air flame
- 2009
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 96:4, s. 645-656
-
Journal article (peer-reviewed)abstract
- Time-resolved laser-induced incandescence (LII) has been developed rapidly during the last decade as a useful non-intrusive technique for particle size determination. Still several parameters should be investigated in order to improve the accuracy of LII for particle sizing and the spatial distribution of the laser energy is one of these. Generally a top-hat profile is recommended, as this ensures a uniform heating of all particles in the measurement volume. As it is generally not straightforward to create a uniform beam profile, it is of interest to establish the influence of various profiles on the evaluated particle sizes. In this work we present both an experimental and a theoretical investigation of the influence of the spatial profile on evaluated sizes. All experiments were carried out using a newly developed setup for two-colour LII (2C-LII) which provides online monitoring of both the spatial and temporal profile as well as the laser pulse energy. The LII measurements were performed in a one-dimensional premixed sooting ethylene/air flame, and evaluated particle sizes from LII were compared with thermophoretically sampled soot particles analysed using transmission electron microscopy (TEM). The results show that although there is some influence of the spatial laser energy distribution on the evaluated particle sizes both in modelling and experiments, this effect is substantially smaller than the influence of the uncertainties in gas temperature and the thermal accommodation coefficient.
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| 21. |
- Bladh, Henrik, et al.
(author)
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On the dependence of the laser-induced incandescence (LII) signal on soot volume fraction for variations in particle size
- 2008
-
In: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. ; 90:1, s. 109-125
-
Journal article (peer-reviewed)abstract
- “The laser-induced incandescence (LII) signal is proportional to soot volume fraction” is an often used statement in scientific papers, and it has – within experimental uncertainties – been validated in comparisons with other diagnostic techniques in several investigations. In 1984 it was shown theoretically in a paper by Melton that there is a deviation from this statement in that the presence of larger particles leads to some overestimation of soot volume fractions. In the present paper we present a detailed theoretical investigation of how the soot particle size influences the relationship between LII signal and soot volume fraction for different experimental conditions. Several parameters have been varied; detection wavelength, time and delay of detection gate, ambient gas temperature and pressure, laser fluence, level of aggregation and spatial profile. Based on these results we are able, firstly, to understand how experimental conditions should be chosen in order to minimize the errors introduced when assuming a linear dependence between the signal and volume fraction and secondly, to obtain knowledge on how to use this information to obtain more accurate soot volume fraction data if the particle size is known.
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| 22. |
- Bood, J., et al.
(author)
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Temperature and concentration measurements in acetylene-nitrogen mixtures in the range 300-600 K using dual-broadband rotational CARS
- 2000
-
In: Applied Physics B. - 0946-2171. ; 70:4, s. 607-620
-
Journal article (peer-reviewed)abstract
- Pure rotational coherent anti-Stokes Raman scattering (CARS) experiments have been performed in acetylene for temperatures ranging from 294 to 582 K, and in mixtures of acetylene and nitrogen in the mole fraction range of 0.06-0.32 for acetylene at room temperature. The experimental spectra are evaluated by a least-square fitting to libraries of theoretically calculated spectra using two different Raman linewidth models, one with and one without dependence on the rotational quantum number J. It is found that a J-dependent model is favourable, both regarding temperature measurements in pure acetylene, and simultaneous acetylene concentration and temperature measurements in different mixtures of acetylene and nitrogen. For the temperature measurements performed in pure acetylene the temperature inaccuracy is generally less than 2% when the J-dependent model for the Raman linewidths is used. It is found that fitting the value of the non-resonant susceptibility significantly improves the quality of the spectral fits and is a requirement for high temperature accuracy with the present model. The evaluated concentrations show a maximum error of 13% on a relative scale. Potential sources of systematical errors both regarding measured temperatures and acetylene concentrations are discussed.
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| 23. |
- Borggren, Jesper, et al.
(author)
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Diode laser-based thermometry using two-line atomic fluorescence of indium and gallium
- 2017
-
In: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 123:12
-
Journal article (peer-reviewed)abstract
- A robust and relatively compact calibration-free thermometric technique using diode lasers two-line atomic fluorescence (TLAF) for reactive flows at atmospheric pressures is investigated. TLAF temperature measurements were conducted using indium and, for the first time, gallium atoms as temperature markers. The temperature was measured in a multi-jet burner running methane/air flames providing variable temperatures ranging from 1600 to 2000 K. Indium and gallium were found to provide a similar accuracy of ~ 2.7% and precision of ~ 1% over the measured temperature range. The reliability of the TLAF thermometry was further tested by performing simultaneous rotational CARS measurements in the same experiments.
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| 24. |
- Borggren, Jesper, et al.
(author)
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Temperature imaging in low-pressure flames using diode laser two-line atomic fluorescence employing a novel indium seeding technique
- 2016
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 122:3
-
Journal article (peer-reviewed)abstract
- The use of diode lasers for spatially resolved temperature imaging is demonstrated in low-pressure premixed methane–air flames using two-line atomic fluorescence of seeded indium atoms. This work features the advantages of using compact diode lasers as the excitation sources with the benefits of two-dimensional planar imaging, which is normally only performed with high-power pulsed lasers. A versatile and reliable seeding technique with minimal impact on flame properties is used to introduce indium atoms into the combustion environment for a wide range of flame equivalence ratios. A spatial resolution of around 210 µm for this calibration-free thermometry technique is achieved for three equivalence ratios at a pressure of 50 mbar in a laminar flat flame.
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| 25. |
- Brackmann, Christian, et al.
(author)
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Characterization of ammonia two-photon laser-induced fluorescence for gas-phase diagnostics
- 2014
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 115:1, s. 25-33
-
Journal article (peer-reviewed)abstract
- Two-photon laser-induced fluorescence (LIF) of ammonia (NH3) with excitation of the C'-X transition at 304.8 nm and fluorescence detection in the 565 nm C'-A band has been investigated, targeting combustion diagnostics. The impact of laser irradiance, temperature, and pressure has been studied, and simulation of NH3-spectra, fitted to experimental data, facilitated interpretation of the results. The LIF-signal showed quadratic dependence on laser irradiance up to 2 GW/cm(2). Stimulated emission, resulting in loss of excited molecules, is induced above 10 GW/cm(2), i.e., above irradiances attainable for LIF imaging. Maximum LIF-signal was obtained for excitation at the 304.8 nm bandhead; however, lower temperature sensitivity over the range 400-700 K can be obtained probing lines around 304.9 nm. A decrease in fluorescence signal was observed with pressure up to 5 bar absolute and attributed to collisional quenching. A detection limit of 800 ppm, at signal-to-noise ratio 1.5, was identified for single-shot LIF imaging over an area of centimeter scale, whereas for single-point measurements, the technique shows potential for sub-ppm detection. Moreover, high-quality NH3-imaging has been achieved in laminar and turbulent premixed flames. Altogether, two-photon fluorescence provides a useful tool for imaging NH3-detection in combustion diagnostics.
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