| 1. |
- Bengtsson, Per Erik, et al.
(författare)
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Rotational cars thermometry in sooting flames
- 1992
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 81:1-3, s. 129-140
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Tidskriftsartikel (refereegranskat)abstract
- Coherent anti-Stokes Raman scattering of pure rotational transitions, rotational CARS, is demonstrated as an efficient method for temperature determination in sooting flames. The dual broadband CARS approach was used to measure temperature profiles in premixed, sooting ethylene flames at atmospheric pressure by probing the nitrogen gas. The recorded spectra were of equally high quality in non-sooting and sooting flames with volume fractions of soot of up to 7 x 10 7 cm3 soot/cm3The advantages of rotational CARS in comparison with several other techniques for the measurement of temperatures in sooting flames, and the general applicability of the technique to different combustion conditions, are discussed. Potential limitations in the application of rotational CARS to sooting flames that are more heavily sooting than the ones investigated in this study, are outlined.
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| 2. |
- Bengtsson, Per-Erik, et al.
(författare)
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Vibrational CARS thermometry in sooty flames: Quantitative evaluation of C2 absorption interference
- 1990
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Ingår i: Combustion and Flame. - 0010-2180. ; 82:2
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Tidskriftsartikel (refereegranskat)abstract
- The application of nitrogen vibrational CARS thermometry to sooty, premixed, atmospheric pressure flames has been investigated using a Nd:YAG laser based system. It was found that laser-produced C2 radicals strongly absorb part of the fundamental band peak in the CARS spectrum. This was the most severe interference to the CARS signal. A quantitative investigation of temperature errors caused by the C2 absorption effect is presented. The correlation between the absorption interference and the soot volume fraction was examined for different flame conditions. Also, the increase of the nonresonant susceptibility in sooty flame regions is clearly illustrated and its effect on thev evaluated temperature is quantitatively determined. The single-shot temperature standard deviation has also been investigated in flames with different soot loadings. Finally, other interference effects to the CARS signals in sooty flames are described and discussed.
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| 3. |
- Da Via, C, et al.
(författare)
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Lightwave Analogue Links For LHC Detector Front-ends
- 1994
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 344:1, s. 199-211
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Tidskriftsartikel (refereegranskat)abstract
- The requirements on optical links for transferring analog and digital signals from the detector front-ends to the readout electronics at future high-luminosity colliders are reviewed. The advantages of external modulation techniques are discussed. An outline is given of the the R&D programme recently started at CERN by a collaboration involving high-energy physics institutes, optoelectronics research laboratories and industry, in order to develop electro-optic intensity modulator arrays, particularly for analogue applications, and to investigate the feasibility of volume production. The design of multichannel demonstrators in lithium niobate and III-V semiconductor technology is described. Preliminary results of the performance measurements are presented.
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| 4. |
- Kröll, Stefan, et al.
(författare)
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Background-free Species Detection In Sooty Flames Using Degenerate 4-wave-mixing
- 1993
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 47:10, s. 1620-1622
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Tidskriftsartikel (refereegranskat)abstract
- The background radiation disturbance in luminous environments has been compared for degenerate four-wave mixing (DFWM) and laser-induced fluorescence (LIF) for OH radical detection in a sooty propane/oxygen flame. The LIF signal generally was considerably stronger than the DFWM signal, but in strongly sooty environments the LIF signal was accompanied by a significant background signal, while the DFWM signal was background-free under all soot loads tested.
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| 5. |
- Kröll, Stefan, et al.
(författare)
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Influence of excited state Pr3+ on the relaxation of the Pr3+-YAlO3 3H4-1D2 transition
- 1991
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Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 44:1, s. 30-34
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Tidskriftsartikel (refereegranskat)abstract
- Two-pulse photon-echo measurements on the 0.1 at. % Pr3+:YAlO3 H-3(4)-D-1(2) transition suggest that the relaxation time depends on the density of excited states created by the excitation pulses. The dependence of the relaxation time on the intensity of each excitation pulse shows that our results are inconsistent with instantaneous spectral diffusion, a model often invoked in this type of experiment, where excited states created by the second pulse chiefly influence the relaxation time. A homogeneous linewidth contribution, noted in previous work as being of unknown origin, is eliminated at low excitation fluences.
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| 6. |
- Kröll, Stefan, et al.
(författare)
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Intensity dependent photon echo relaxation in rare earth doped crystals
- 1990
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Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 41:16, s. 11568-11571
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Tidskriftsartikel (refereegranskat)abstract
- Photon-echo-relaxation measurements made on the 3H4-3P0 transition of 0.01 at. % Pr3+:YAG (where YAG represents yttrium aluminum garnet), 3H4-1D2 transition in 0.1 at. % Pr3+:YAlO3, and 7F0-5D0 transition in 0.25 at. % Eu3+:YAlO3 show that the photon-echo relaxation rate increases when the intensities of the excitation pulses are increased. Although a part of the relaxation-rate increase in Pr3+:YAG may be attributed to an instantaneous spectral diffusion (ISD) in which the presence of excited neighboring Pr3+ ions change the local field and the absorption frequency of the rare-earth ions, our data deviate significantly from the ISD-model predictions. An additional intensity-dependent relaxation mechanism is required to explain the results.
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| 7. |
- Kröll, Stefan, et al.
(författare)
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Photon-echo-based logical processing
- 1993
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Ingår i: Optics Letters. - 0146-9592. ; 18:21, s. 1834-1836
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Tidskriftsartikel (refereegranskat)abstract
- Word-by-word logical AND and OR operation with photon-echo processing is demonstrated for what is to our knowledge the first time. The photon-echo process can store sequences of optical data before processing. The present logical operations on 8- and 4-bit words are performed by using single-shot frequency-chirped photon echoes. Data rates of approximately 1 MHz, input energies of 1-10 nJ/bit, and output energies in the picojoule-per-bit range are demonstrated by using a transition with a transition probability of only 20 s(-1).
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| 8. |
- Kröll, Stefan, et al.
(författare)
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Recording Density Limit of Photon-echo Optical Storage With High-speed Writing and Reading
- 1993
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Ingår i: Optical Society of America. Journal B: Optical Physics. - 0740-3224. ; 32:35, s. 7233-7242
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Tidskriftsartikel (refereegranskat)abstract
- The first analysis to our knowledge of the optical data storage density of photon-echo storage is presented. Mainly considering signal-to-noise ratio performance, we calculate the obtainable storage density for data storage and processing using photon echoes to be approximately 100 times the theoretical limit for conventional optical data storage. This limit is similar to that theoretically calculated for data storage by use of persistent spectral hole burning. For storage times longer than the upper-state lifetime the highest densities can, however, be obtained only if all the excited atoms decay, or are transferred, to a different state than that from which they were originally excited. The analysis is restricted to samples with low optical density, and it also assumes that for every data sequence, writing is performed only once. It is therefore not directly applicable to accumulated photon echoes. A significant feature of photon-echo storage and processing is its speed; e.g., addressing 1 kbyte/(spatial point) permits terahertz read and write speeds for transitions with transition probabilities as low as 1000 s-1.
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| 9. |
- Martinsson, Lars, et al.
(författare)
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A test of different rotational Raman linewidth models: Accuracy of rotational coherent anti-Stokes Raman scattering thermometry in nitrogen from 295 to 1850 K
- 1993
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 99:4, s. 2466-2477
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Tidskriftsartikel (refereegranskat)abstract
- Rotational Raman linewidths calculated from three different models have been used in temperature measurements by rotational coherent anti-Stokes Raman scattering (CARS)—a semiclassical ab initio model, the modified exponential energy gap model (MEG), and the energy corrected sudden scaling law (ECS). Experimental rotational CARS spectra were generated, using the dual-broadband approach, in pure nitrogen at atmospheric pressure in a heat pipe in the temperature range from 295 to 1850 K. Below 1500 K, the temperatures evaluated using the ECS linewidths agreed with the heat-pipe temperatures to within 20 K. Above 1500 K, the errors in the evaluated temperatures increased steeply for all linewidth models, reaching errors of several hundreds of Kelvins at 1850 K. This behavior of the evaluated temperature is probably caused by the uncertainty in the values of the rotational Raman linewidths for high rotational states at high temperatures. This work therefore illustrates that rotational CARS can be used for experimentally studying Raman linewidths and in particular their dependence on temperature and rotational quantum number. The influence of different experimental parameters on the evaluated temperatures is discussed, and the spectral synthesis program is presented. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.
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| 10. |
- Sunesson, A, et al.
(författare)
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Laser Triggering of Electric Breakdown In Liquids
- 1994
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - : Institute of Electrical and Electronics Engineers (IEEE). - 1070-9878. ; 1:4, s. 680-691
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Tidskriftsartikel (refereegranskat)abstract
- Electric breakdown in semihomogeneous geometries has been studied in n-hexane and transformer oil using a laser triggering method for fields far below the spontaneous breakdown field. The method uses a laser-produced plasma to initiate the breakdown. Strong self focusing in the liquids was limited by increasing the numerical aperture of the laser beam to > 0.20 prior to focusing. Electrical breakdown could be triggered at fields as low as 50 kV/cm in transformer oil and 25 kV/cm for n-hexane. The time lags are between 30 and 200 mus, depending on voltage, liquid, and gap size. Current and light emission measurements of the prebreakdown phenomena are presented and a model for the triggering process is proposed.
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