| 1. |
- Afzelius, Mikael, et al.
(author)
-
Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. I. Inter-branch interference effect
- 2002
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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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| 2. |
- 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
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 75:6-7, s. 771-778
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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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| 3. |
- Alnis, Janis, et al.
(author)
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Laser spectroscopy of free molecular oxygen dispersed in wood materials
- 2003
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 77:6-7, s. 691-695
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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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| 4. |
- 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
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 72:3, s. 367-372
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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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| 5. |
- Balcou, P, et al.
(author)
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High-order-harmonic generation: towards laser-induced phase-matching control and relativistic effects
- 2002
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 74:6, s. 509-515
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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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| 6. |
- 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
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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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| 7. |
- 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
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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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| 8. |
- Denker, Boris, et al.
(author)
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Luminescent and laser properties of Yb-Er:GdCa4O(BO3)3 : a new crystal for eye-safe 1.5-µm lasers
- 2004
-
In: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 79:5, s. 577-581
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Journal article (peer-reviewed)abstract
- We present for the first time 1.5-μm laser emission in Yb-Er:GdCa 4O(BO3)3 (GdCOB). The crystals were grown by the Czochralski method from platinum crucibles. Spectroscopic and laser tests of the crystals are described. A continuous-wave output power of 80 mW was achieved in a monolithic microchip cavity under laser-diode pumping.
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| 9. |
- Dreyer, C, et al.
(author)
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Raman scattering at 532 and 355 nm in atmospheric pressure propane/air flames, with and without liquid fuels
- 2004
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 79:1, s. 121-130
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Journal article (peer-reviewed)abstract
- We discuss an experimental investigation of Raman scattering spectroscopy in the vicinity of a simulated reacting liquid fuel spray. Spray flames are known to produce interference from droplet elastic scattering, laser-induced fluorescence, and laser-induced incandescence of soot. The goal in this work is to evaluate various experimental approaches to this challenging problem. We evaluate Raman scattering from both 532 and 355 nm beams (second and third harmonics of Nd : YAG), at various polarization orientations and over various lifetimes. We discuss tradeoffs between the various approaches and identify operating regimes in which such Raman measurements are possible. Perhaps the most compelling finding of this work is that the third harmonic of Nd : YAG holds more promise for measurement in high-pressure, combusting spray environments than has been previously thought.
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| 10. |
- Gustafsson, U, et al.
(author)
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Simultaneous detection of methane, oxygen and water vapour utilising near-infrared diode lasers in conjunction with difference-frequency generation
- 2000
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 71:6, s. 853-857
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Journal article (peer-reviewed)abstract
- An all-diode-laser-based spectrometer is used for the simultaneous detection of methane, oxygen and water vapour. This is accomplished using a 760-nm diode laser and a 980-nm diode laser in conjunction with difference-frequency generation to 3.4 mum in a periodically poled lithium niobate crystal. Each of the output wavelengths is resonant with one of the molecular species. Simultaneous recordings over a 15-m open path of laboratory air are demonstrated. The recording scheme shows the wide applicability of a diode-laser-based difference-frequency spectrometer for the detection of molecular species in different wavelength ranges. By increasing the frequency of the 760-nm diode laser and decreasing the frequency of the 980-nm diode laser, a maximum continuous tuning range in the mid infrared of 3.6 cm(-1) is achieved. This enables the recording of several methane lines at atmospheric pressure. Pressure-dependence studies of methane lineshapes are also performed in an absorption cell. An indoor-air methane background level of 3 ppm is measured. The signal-to-noise ratio in the recorded methane spectra indicates that sub-ppm detection of methane at atmospheric pressure is feasible.
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| 11. |
- Holmlid, Leif, 1942
(author)
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Detection of frequency red shifts and blue shifts for single-mode IR laser radiation in Rydberg matter
- 2004
-
In: Applied Physics B-Lasers and Optics. - : Springer Science and Business Media LLC. ; 79:7, s. 871-877
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Journal article (peer-reviewed)abstract
- Stimulated emission and laser gain were recently reported for the excited condensed matter Rydberg matter (RM). This shows that RM is in an excited and inverted state. A low-intensity single-mode IR laser beam is here red shifted in reflection from a layer of RM, and blue shifted when it passes through a cloud of RM. The shifts of approximately 0.02 cm(-1) are observed with a temperature-stable Fabry-Perot interferometer. The process giving the wavelength shifts is proposed to be stimulated Raman scattering. RM is here formed from Rydberg states of both K atoms and nitrogen molecules inside a vacuum chamber, and it may be in liquid or solid form.
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| 12. |
- Kaminski, Clemens, et al.
(author)
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Flame growth and wrinkling in a turbulent flow
- 2000
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In: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 71:5, s. 711-716
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Journal article (peer-reviewed)abstract
- High-speed planar laser-induced fluorescence (PLIF) and 3-D large eddy simulations (LES) are used to study turbulent flame kernel growth, wrinkling and the formation of separated flame pockets in methane/air mixtures. Turbulence was effected by a set of rotary fans situated in a cylindrical enclosure. Flame wrinkling was followed on sequential 2-D OH images captured at kHz repetition rates. Under stoichiometric conditions and low turbulence levels the flame kernel remains singly connected and close to spherical in shape. By increasing turbulence or reducing the stoichiometry of the mixture the formation of separated pockets could be observed and studied. The mechanisms behind these phenomena are investigated qualitatively by LES of a level-set G-equation describing the flame surface propagation in turbulent flows.
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| 13. |
- Karlsson, G., et al.
(author)
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Development and characterization of Yb-Er laser glass for high average power laser diode pumping
- 2002
-
In: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 75:1, s. 41-46
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Journal article (peer-reviewed)abstract
- A new strong erbium laser glass (SELG) based on a boro-alumo-phosphate composition is reported. We discuss the synthesis and chemical properties together with spectroscopic and thermo-mechanical data. The new glass composition shows excellent laser performance and withstands high-average power pump radiation. We present laser results at 1.54 mum from flashlamp and laser pumping. In tests with laser-diode pumped Q-switched Er-Yb microchip lasers, we have achieved up to 150 mW of average output power and generated 1.2 kW in peak power. Co2+:MgAl2O4 was here used as the saturable absorber.
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| 14. |
- Korkishko, Y. N., et al.
(author)
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Second-order optical non-linearity of proton exchanged lithium tantalate waveguides
- 2001
-
In: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 73:06-maj, s. 519-522
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Journal article (peer-reviewed)abstract
- A detailed correlation between the fabrication conditions, crystallographic phase state of HxLi1-xTaO3 waveguides and second-order optical non-linearity has been investigated by using reflected SHG measurements from the polished waveguide end face. The non-linearity, strongly reduced after the initial proton exchange, is found to be restored and even increased after annealing. However, this apparent increase in the non-linearity is accompanied by a strong degradation of the quality of the SHG reflected beam in the region of the initial as-exchanged waveguide due to beam scattering. The high temperature proton exchange technique has been shown to produce high-quality alpha -phase waveguides with essentially undegraded non-linear optical properties. There is no phase transition when the alpha -phase waveguides are fabricated by direct exchange. This phase presents the same crystalline structure as that of LiTaO3 and maintains the excellent non-linear properties of the bulk material. The results obtained are important for the design fabrication and optimization of guided-wave non-linear optical devices in LiTaO3.
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| 15. |
- Li, Zhongshan, et al.
(author)
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Detection of methane with mid-infrared polarization spectroscopy
- 2004
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 79:2, s. 135-138
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Journal article (peer-reviewed)abstract
- We report on the application of polarization spectroscopy in the midinfrared spectral region for the detection of methane by probing its asymmetric ro-vibrational transitions. Tunable infrared laser radiation, near 3.4 mum, was obtained from difference-frequency generation in a LiNbO3 crystal. Infrared polarization spectroscopy (IRPS) spectra of the P, Q and R branches of the nu(3) band, recorded with both linearly and circularly polarized pump beams, are presented. The experiments were performed in an atmospheric pressure gas jet with methane diluted with Ar. An IRPS spectrum with signal-to-noise ratio better than 10(4) was observed. The dependence of the IRPS signal intensity on the methane mole fraction and on the pumping laser power density was investigated.
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| 16. |
- Lindström, Torgny, et al.
(author)
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Analysis of lidar measurements using nonparametric kernel regression methods
- 2002
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 74:2, s. 155-165
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Journal article (peer-reviewed)abstract
- The lidar technique is an efficient tool for remote monitoring of the distribution of a number of atmospheric species. We study measurements of sulphur dioxide emitted from the Italian volcano Mt. Etna. This study is focused on the treatment of data and on the procedure to evaluate range-resolved concentrations. In order to make an in-depth analysis, the lidar system was prepared to store measurements of individual backscattered laser pulses. Utilizing these repeated measurements a comparison of three different methods to average the returned signals is made. In the evaluation process we use local polynomial regression to estimate the range-resolved concentrations. Here we calculate optimal bandwidths based on the empirical-bias bandwidth selector. We also compare two different variance estimators for the path-integrated curves: local polynomial variance estimation and variance estimation based on Taylor approximations. Results show that the method performs well. An advantage compared to previous methods for evaluation of lidar measurements is that an estimate of the mean squared error of the estimated concentration can be calculated.
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| 17. |
- Lognoli, D, et al.
(author)
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Fluorescence lidar imaging of the cathedral and baptistery of Parma
- 2003
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 76:4, s. 457-465
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Journal article (peer-reviewed)abstract
- Extensive fluorescence multispectral imaging of the cathedral and baptistery of Parma, Italy, is reported and discussed. In particular, the first fluorescence imaging data from protection-treated stony materials were recorded. Fluorescence spectra were taken with a mobile lidar system scanning the monument surfaces with a frequency-tripled Nd:YAG laser beam from a distance of about 80 m. For each pixel of the area investigated, a high-spectral-resolution spectrum in the full visible range was acquired. The principal-component analysis technique was used to obtain thematic maps that outlined areas subject to protective treatment and biological growth, and other features, such as different types of stones and decoration pigments.
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| 18. |
- Lopez, Rodrigo, et al.
(author)
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Characterization of high-order harmonic radiation on femtosecond and attosecond time scales
- 2004
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 78:7-8, s. 835-840
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Journal article (peer-reviewed)abstract
- We characterize the temporal structure of high-order harmonic radiation on both the femtosecond and attosecond time scales. The harmonic emission is characterized by mixed-color two-photon ionization with an infrared femtosecond laser using a Mach-Zehnder interferometer where both pump and probe arms travel completely separate paths. In a first experiment, we measure the duration and chirp of individual harmonics. In a second experiment, we resolve, for the first time with this type of setup, the attosecond beating of several harmonics generated under conditions similar to the first experiment. We suggest that the results of both measurements can be combined to determine the full attosecond time structure of the harmonic emission.
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| 19. |
- Lynga, C, et al.
(author)
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A laser system providing tunable, narrow-band radiation from 35 nm to 2 mu m
- 2001
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 72:8, s. 913-920
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Journal article (peer-reviewed)abstract
- We describe a laser system that readily provides radiation tunable from 2 mum in the infra-red to 35 nm in the extreme ultraviolet spectral range. The broad spectral range is covered through a range of non-linear processes such as Raman shifting and high-order harmonic generation. Pulses with duration of tens of picoseconds are obtained. The relative bandwidth of the radiation is delta lambda/lambda = 10(-4), comparable with what can be achieved by using high-resolution monochromators at state-of-the-art synchrotron beamlines. We discuss different methods for characterising the radiation in this wide wavelength regime. We also discuss the capabilities of the system from the measured parameters.
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| 20. |
- Omrane, Alaa, et al.
(author)
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2D-temperature imaging of single droplets and sprays using thermographic phosphors
- 2004
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 79:4, s. 431-434
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Journal article (peer-reviewed)abstract
- A novel 2D-technique for temperature visualization of single droplets and sprays is presented. Laser induced emission from thermographic phosphor seeded to the investigated liquid was detected by a fast framing camera. The subsequent phosphorescence images measured by seven consecutively gated CCD detectors allowed pixel-to-pixel lifetime evaluation of the phosphorescence emission. The temperature at each pixel position was evaluated using a calibration procedure of temperature against lifetime. These measurements were applied first to a free falling water based droplet, then to a suspended droplet in an ultrasonic levitator. Finally, the technique was applied to spray.
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| 21. |
- Peltz, M., et al.
(author)
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Optical parametric oscillators for high pulse energy and high average power operation based on large aperture periodically poled KTP and RTA
- 2001
-
In: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 73:7, s. 663-670
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Journal article (peer-reviewed)abstract
- We report on optical parametric oscillators (OPOs) based on large aperture periodically poled KTiOPO4 (PPKTP) and RbTiOAsO4 (PPRTA) pumped with high pulse energy and high average power Q-switched solid-state lasers. The OPOs were pumped with 1064-nm pulses of a diode-pumped Nd:YVO4 laser at 20 kHz repetition rate. The emitted signal wavelengths were 1.72 mum and 1.58 mum and the idler wavelengths were 2.79 mum and 3.26 mum, respectively. Pumping the PPKTP OPO with 7.2 W and the PPRTA OPO with 8 W average power, 2 W and 1.3 W total OPO output powers were generated. Two-dimensional measurements of the total OPO output power, the signal wavelength and the signal bandwidth in dependence on the crystal location indicated a good uniformity of the quasi phase matching structure over the entire 3-mm-thick crystals. This allowed pumping with larger pump beams and therefore with pulse energies of tens of millijoules. Pumping with different flash-lamp-pumped lasers, good OPO performance and high output pulse energies could be achieved for all pump lasers. Maximum input pulse energies of 56 mJ gave output pulse energies of as much as 18 mJ. The temperature tuning behaviors of both OPOs were measured, showing excellent agreement with calculated temperature tuning curves. New equations for temperature dispersion in RTA are presented. These results show that large-aperture PPKTP and PPRTA crystals are well suited for tunable nanosecond OPO operation with multi-watt average pump power and several tens of millijoules pump pulse energies.
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| 22. |
- Petra, Stefan JH, et al.
(author)
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Atom lithography with two-dimensional optical masks
- 2004
-
In: Applied physics. B, Lasers and optics (Print). - New York : Springer. - 0946-2171 .- 1432-0649. ; 79:3, s. 279-283
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Journal article (peer-reviewed)abstract
- With a two-dimensional (2D) optical mask at lambda=1083 nm, nanoscale patterns are created for the first time in an atom lithography process using metastable helium atoms. The internal energy of the atoms is used to locally damage a hydrophobic resist layer, which is removed in a wet etching process. Experiments have been performed with several polarizations for the optical mask, resulting in different intensity patterns, and corresponding nanoscale structures. The results for a linear polarized light field show an array of holes with a diameter of 260 nm, in agreement with a computed pattern. With a circularly polarized light field a line pattern is observed with a spacing of lambdaroot2=766 nm. Simulations taking into account many possible experimental imperfections can not explain this pattern.
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| 23. |
- Spiekermann, Stefan, et al.
(author)
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Optimizing non-resonant frequency conversion in periodically poled media
- 2004
-
In: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 79:2, s. 211-219
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Journal article (peer-reviewed)abstract
- Non-resonant frequency conversion into the blue, green, orange, and red spectral regions is reported. Fundamental light sources were continuous-wave non-planar monolithic single-mode ring Nd: YAG lasers as well as a standing-wave multi-mode Nd: YAG laser. Periodically poled KTiOPO4 was employed as the nonlinear medium, but the considerations could also be applied to other periodically poled materials. A multi-pass scheme resulted in a normalized conversion efficiency as high as 27.2 % W-1 for frequency doubling in the small-signal regime at 1064 nm.
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| 24. |
- Strelkov, V, et al.
(author)
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Generation of attosecond pulses with ellipticity-modulated fundamental
- 2004
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 78:7-8, s. 879-884
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Journal article (peer-reviewed)abstract
- We have studied experimentally and theoretically high-order harmonic generation using a laser field with a time-dependent ellipticity. We show that the harmonic emission can be confined into a narrow temporal window, in which the fundamental polarization is quasi-linear. This allows a single attosecond pulse (200 as) with a fundamental field obtained from 10 fs pulse to be generated.
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| 25. |
- Vogt, Ulrich, et al.
(author)
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High-resolution spatial characterization of laser produced plasmas at soft x-ray wavelengths
- 2004
-
In: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 78:1, s. 53-58
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Journal article (peer-reviewed)abstract
- In this article, we describe the setup and application of a system for the spatial characterization of laser-produced plasma x-ray sources. While pinhole cameras are normally used for this purpose, we employed a zone plate to act as the x-ray lens. Together with an x-ray CCD camera as the detector, a spatial resolution of up to 2 mum was achieved. Due to the wavelength-dependent focal length of a zone plate, the monochromaticity of the image was better than lambda/Deltalambda=150, and the large aperture of the zone plate allowed single-laser-shot images to be collected. Methanol and ethanol were used as liquid-jet target systems. Two different Nd:YAG lasers with pulse durations of 3 ns and 10 ns produced the plasmas. Our measurements concentrated on the line emission of carbon in the soft x-ray spectral range, namely, the hydrogen-like alpha-line at 3.37 nm and the helium-like alpha-line at 4.03 nm. We investigated the influence of different nozzle sizes, laser energies, and pulse durations on the source size of the plasma. Depending on the experimental conditions, plasma diameters of 17-60 mum were measured.
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| 26. |
- Walewski, Joachim, et al.
(author)
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Soot visualisation by use of laser-induced soot vapourisation in combination with polarisation spectroscopy
- 2003
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 77:4, s. 447-454
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Journal article (peer-reviewed)abstract
- A novel approach to the visualisation of soot is presented. It relies on a combination of laser-induced soot vapourisation and consecutive polarisation spectroscopy. Upon soot vapourisation, molecular fragments (for example, C-2) emerge, and may serve as effective tracers for soot. In this study we demonstrate that saturated polarisation spectroscopy on photoinduced C-2 can be exploited for soot detection. Signal maps featuring high signal-to-noise ratios were readily recorded in ethyne-rich flames and any spurious background, for example, caused by Rayleigh scattering, was successfully suppressed by means of spatial filtering. Additionally, investigations were carried out addressing how the attained signals correlate with local soot volumne fractions. For this purpose, height profiles of C-2 number densities inferred from the polarisation spectroscopy signal maps were compared with profiles of the soot volumne fraction inferred from measurements with laser-induced incandescence. For low soot volumne fractions, the shapes of the height profiles from our approach agree rather well with the latter; they do not agree for higher soot volumne fractions. Further investigation is required to resolve this discrepancy. Scattering from particles in the Mie scattering range may hamper the application of this approach, and avenues are suggested for extending the applicability of the approach presented to large soot particles.
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| 27. |
- Weibring, Petter, et al.
(author)
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Multi-component chemical analysis of gas mixtures using a continuously tuneable lidar system
- 2004
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 79:4, s. 525-530
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Journal article (peer-reviewed)abstract
- Differential absorption lidar (DIAL) measurements are usually made on single compounds by alternately switching the wavelength between on and off a resonance line. The selection of more than two wavelengths is a mathematical necessity for simultaneous measurement of multiple species or for resolving interference effects between a compound of interest and a background gas such as water vapour or carbon dioxide. This is especially true in the mid-IR region, where many hydrocarbon compounds have important spectral features. We present a method for remote measurement of gas mixtures in the mid-IR region based on a newly developed fast-switching, frequency-agile optical parametric oscillator lidar transmitter. A multivariate statistical procedure has also been applied for this system, which combines a genetic algorithm for wavelength selection with a partial least squares method for identifying individual compounds from their combined absorption spectrum. A calibration transfer is performed for compounds of interest using reference spectra from an absorption spectra database. Both indoor absorption cell measurements and outdoor remote range resolved measurements of hydrocarbon mixtures were performed to explore the performance of the method.
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| 28. |
- Zair, A, et al.
(author)
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Time-resolved measurements of high order harmonics confined by polarization gating
- 2004
-
In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 78:7-8, s. 869-872
-
Journal article (peer-reviewed)abstract
- We investigate the temporal confinement of high order harmonic pulses generated by a femtosecond (fs) infrared (IR) pulse with a time varying polarization. We use a set of two birefringent quartz plates to modulate the IR polarization. It produces a short temporal gate of linear polarization where harmonics are efficiently generated during a small fraction of the IR pulse. By rotating one of the plates, the gate width can be continuously varied between 70 fs down to 7 fs. The XUV pulse duration is measured by cross-correlation with a probe IR pulse of 12 fs. When the gate width is decreased, a clear temporal confinement of the XUV emission is observed through the cross correlation signal. This experiment is the first direct experimental evidence in the temporal domain that the polarization gating technique can be used to significantly shorten the harmonic pulse duration.
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| 29. |
- 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
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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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| 30. |
- Cassettari, D, et al.
(author)
-
Micromanipulation of neutral atoms with nanofabricated structures
- 2000
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In: APPLIED PHYSICS B-LASERS AND OPTICS. - : SPRINGER VERLAG. - 0946-2171. ; 70:5, s. 721-730
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Journal article (peer-reviewed)abstract
- A large variety of trapping and guiding potentials can be designed by bringing cold atoms close to charged or current cal lying material objects. We describe the basic principles of constructing microscopic traps and guides and how to load atoms into them
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| 31. |
- Ohno, Masahide, et al.
(author)
-
The interference effect in Auger-photoelectron coincidence spectroscopy
- 2003
-
In: J. Phys. B: At. Mol. Opt. Phys.. - : IOP Publishing. - 0946-2171. ; 36, s. 4519-4533
-
Journal article (peer-reviewed)abstract
- When core-hole decay develops along two different paths, i.e. by a direct Auger-transition path and by an indirect path passing via two-hole–one-particle excitation and de-excitation, the screening of the direct Auger-transition matrix element by the particle–hole (de-)excitations leads to a pronounced interference effect in the Auger-electron emission. The manifestation of the interference effect in the Auger-photoelectron coincidence spectroscopy spectrum is discussed in the light of the unique capabilities of the coincidence measurements.
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| 32. |
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