| 1. |
- Barmann, P, et al.
(författare)
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Spatially and temporally resolved electron density measurements in streamers in dielectric liquids
- 1997
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 30:5, s. 856-863
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Tidskriftsartikel (refereegranskat)abstract
- Spatially and temporally resolved spectroscopic measurements of light emitted from positive streamers in transformer oil are presented. Analyses of the measurements performed with a DC needle-plane gap yield electron densities and indications of the atomic excitation temperatures in the streamers. The hydrogen emission reveals an electron density below 10(16) cm(-3) during the main part of the streamer propagation time (80-90%). Later the light is also characterized by emission from a high-density plasma with electron densities in the range 10(18)-10(19) cm(-3). The electron density during this time increases approximately linearly with distance from the initiation point and a density factor of four higher has been measured at the streamer tip than at the root. Measurements with high spectral resolution detect both high and low electron densities simultaneously. A tentative model of the interior of the streamer plasma, spatially resolved, is presented.
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| 2. |
- Barmann, P, et al.
(författare)
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Spectroscopic measurements of streamer filaments in electric breakdown in a dielectric liquid
- 1996
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 29:5, s. 1188-1196
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Tidskriftsartikel (refereegranskat)abstract
- Emission spectroscopy has been utilized to provide information about the electron density and temperature in streamers and breakdown arcs in transformer oil. Recorded spectra include strongly broadened hydrogen Balmer-alpha lines and vibration/rotation band profiles of the C-2 molecule. The origin of the observed broadening of hydrogen lines is discussed and it is concluded that it arises mainly from collisions with charged particles, so-called dynamic Stark broadening. By assuming that the broadening is due solely to dynamic Stark broadening, electron densities between 1 x 10(18) and 1 x 10(19) cm(-3) were obtained for the rear of positive streamer filaments during the later stages of propagation. For negative streamers we obtained an upper limit of 3 x 10(16) cm(-3) and for breakdown arcs electron densities up to 4 x 10(18) cm(-3). The temperature information in the C-2 emission profiles and the intensity ratio of the hydrogen Balmer lines are discussed. Rough estimations of the temperature are presented both for positive and for negative streamers.
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| 3. |
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| 4. |
- Dyke, T.R., et al.
(författare)
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Experimental demonstration of data erasure for time-domain optical memories
- 1999
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Ingår i: Optical Society of America. Journal B: Optical Physics. - 0740-3224. ; 16:5, s. 805-811
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Tidskriftsartikel (refereegranskat)abstract
- Data erasure is considered an essential requirement for a practical optical time-domain memory, and it requires that the laser used have very good frequency stability. Such a laser is developed for this work, and data erasure is demonstrated with a sample of YSiO5:Eu3+ for write/rewrite pulse sequences of up to a duration of 100 μs. This is two orders of magnitude longer than had been achieved previously. Phase-sensitive detection is introduced and is shown to be invaluable for monitoring the write, rewrite, and read processes.
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| 5. |
- Elman, U., et al.
(författare)
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Influence of laser phase and frequency fluctuations on photon-echo data erasure
- 1996
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Ingår i: Optical Society of America. Journal B: Optical Physics. - 0740-3224. ; 13:9, s. 1905-1915
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Tidskriftsartikel (refereegranskat)abstract
- Erasure of data stored by use of photon echoes has been investigated as a function of data writing time and data storage time. The results clarify the requirements on laser phase and frequency stability for performing photon-echo data erasure. The analysis of phase and frequency stability of a light source by the photon-echo erasure process is illustrated. A theoretical analysis emphasizing the physical processes that affect the erasure efficiency as well as an extensive discussion of possible error sources are given. Finally, an approach to bit-selective photon-echo data erasure that is insensitive to laser phase and frequency fluctuations is suggested.
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| 6. |
- Elman, U., et al.
(författare)
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Statistical modeling and theoretical analysis of the influence of laser phase fluctuations on photon echo data erasure and stimulated photon echoes
- 1996
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Ingår i: Laser Physics. - 1054-660X. ; 6:4, s. 721-728
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Tidskriftsartikel (refereegranskat)abstract
- The effect of random laser phase fluctuations on stimulated photon echoes (SPEs) and on coherently added SPEs was studied and evaluated both experimentally and analytically with statistical methods. The general concept of describing laser frequency fluctuations as a stationary stochastic process is presented and applied to three specific SPE configurations. The effect of phase fluctuations on erasing an SPE by coherently adding another SPE, phase-shifted by 180 degrees relative to the first, is presented.
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| 7. |
- Luo, B., et al.
(författare)
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Amplification of photon echo signals by use of a fiber amplifier
- 1998
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Ingår i: Optics Letters. - 0146-9592. ; 23:6, s. 442-444
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency of photon-echo processes typically lies in the 0.1–1% range. For many photon-echo-based applications suggested in optical storage and all-optical communication the photon-echo output pulses would need to be used as input data to a new photon-echo process. In such cases amplification of the photon-echo output signals would be necessary for an acceptable signal-to-noise ratio to be obtained. We show that a Pr-doped ZBLAN fiber is able to produce significant amplification of photon-echo signals generated in Pr-doped Y2SiO5 at 606 nm.
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| 8. |
- Luo, B. Z, et al.
(författare)
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Observation of a magnetic-field-induced resonance in the homogeneous dephasing time for the D-1(2)-H-3(4) transition in Pr3+:YAlO3
- 1996
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Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 54:14, s. 9834-9839
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Tidskriftsartikel (refereegranskat)abstract
- Using two-pulse photon echo excitation a strong resonance in the measured homogeneous dephasing time as a function of magnetic field is observed in the H-3(4)-D-1(2) transition of Pr3+:YAlO3. The resonance could only be observed at low excitation energies since it otherwise was masked by excitation intensity dependent extra dephasing processes in the crystal. Thus intensity dependent dephasing processes may not only affect the apparent dephasing time of a system but may also mask other more subtle interactions in the materials studied. It is reasonable to assume that the type of resonance observed could be caused by Zeeman induced level crossings in the active ion or in the host crystal ions or, possibly, that it could be due to coincidences between Zeeman level transition frequencies. However, based on current data of the Pr:YAlO3 system the observed resonance could not be unambiguously tied to such effects.
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| 9. |
- Menager, L., et al.
(författare)
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Time-domain Fresnel-to-Fraunhofer diffraction with photon echoes
- 1999
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Ingår i: Optics Letters. - 0146-9592. ; 24:14, s. 927-929
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Tidskriftsartikel (refereegranskat)abstract
- A photon echo experiment in Tm3+:YAG is reported that shows, for the first time to the authors’ knowledge, the time-domain equivalent of the transition from near- to far-field diffraction, including Talbot self-imaging effects. The experiment demonstrates the huge dispersion capability of photon echoes and opens the way to further exploration of space–time duality.
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| 10. |
- Mohan, R. K, et al.
(författare)
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Bit selective erasure of photon-echo data using Ti : S and dye laser systems: a comparative analysis
- 1998
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Ingår i: Optics Communications. - 0030-4018. ; 158:1-6, s. 149-158
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Tidskriftsartikel (refereegranskat)abstract
- It is investigated how the erasure efficiency for a single bit of data, stored using photon echoes, depends on the data writing time and data storage time. A comparative analysis of the erasure efficiency using a Ti:S laser system and a ring dye laser system is performed. The results clearly establish that the Ti:S laser system, which has a narrower line width than the dye laser system, could be used for efficient erasure over a much larger range of data writing and data storage times. A simple threshold detection-based scheme to convert the photon-echo signals into bits is also used to compare the performances of the two laser systems. A surprising but encouraging result was that it may not be absolutely necessary to have a very high erasure efficiency in an operable photon-echo storage system. (C) 1998 Elsevier Science B.V. All rights reserved.
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