| 21. |
- Glinec, Yannick, et al.
(författare)
-
Evolution of energy spectrum from laser-accelerated protons with a 100 fs intense prepulse
- 2008
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 93:2-3, s. 317-321
-
Tidskriftsartikel (refereegranskat)abstract
- A parametric study is reported where a femtosecond prepulse is used to change the target properties before the interaction with a multi-terawatt laser pulse which accelerates protons from a foil target. The proton spectrum as function of the prepulse delay and intensity, up to 1.5 ns and up to 3x106 W/cm2, respectively, shows a global decrease of the maximum proton energy with delay and intensity. However, under appropriate conditions, it is found that the maximum proton energy increases by more than 10% and that the spectral shape changes.
|
|
| 22. |
- Gopal, A., et al.
(författare)
-
MegaGauss magnetic field generation by ultra-short pulses at relativistic intensities
- 2013
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 55:3
-
Tidskriftsartikel (refereegranskat)abstract
- We report the experimental studies on megaGauss magnetic field generation using a 35 femtosecond laser at relativistic intensities. The polarization change of the self-generated harmonics was recorded to estimate the magnetic field. A parameter scan was performed by varying the input laser intensity as well as the contrast ratio. External optical probing diagnostics were performed using the second harmonic of the incident laser. Additionally, the optical transition radiation from the rear of the target was also recorded.
|
|
| 23. |
- Hansson, Martin, et al.
(författare)
-
Down-ramp injection and independently controlled acceleration of electrons in a tailored laser wakefield accelerator
- 2015
-
Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 18:7
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a study on controlled injection of electrons into the accelerating phase of a plasma wakefield accelerator by tailoring the target density distribution using two independent sources of gas. The tailored density distribution is achieved experimentally by inserting a narrow nozzle, with an orifice diameter of only 400 mu m, into a jet of gas supplied from a 2 mm diameter nozzle. The combination of these two nozzles is used to create two regions of different density connected by a density gradient. Using this setup we show independent control of the charge and energy distribution of the bunches of accelerated electron as well as decreased shot-to-shot fluctuations in these quantities compared to self-injection in a single gas jet. Although the energy spectra are broad after injection, simulations show that further acceleration acts to compress the energy distribution and to yield peaked energy spectra.
|
|
| 24. |
- Hansson, Martin, et al.
(författare)
-
Enhanced stability of laser wakefield acceleration using dielectric capillary tubes
- 2014
-
Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:3
-
Tidskriftsartikel (refereegranskat)abstract
- The stability of beams of laser wakefield accelerated electrons in dielectric capillary tubes is experimentally investigated. These beams are found to be more stable in charge and pointing than the corresponding beams of electrons accelerated in a gas jet. Electron beams with an average charge of 43 pC and a standard deviation of 14% are generated. The fluctuations in charge are partly correlated to fluctuations in laser pulse energy. The pointing scatter of the electron beams is measured to be as low as 0.8 mrad (rms). High laser beam pointing stability improved the stability of the electron beams.
|
|
| 25. |
- Herrlin, K, et al.
(författare)
-
Generation of X-rays For Medical Imaging By High-power Lasers - Preliminary-results
- 1993
-
Ingår i: Radiology. - 1527-1315. ; 189:1, s. 65-68
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To evaluate the use of x-ray imaging performed with a high-power laser system in biologic and medical studies. MATERIALS AND METHODS: A compact terawatt laser system based on chirped pulse amplification in titanium-doped sapphire was used. X rays were generated by irradiating a high-atomic-number target (tantalum). RESULTS: When photons with an energy below 10 keV were removed with use of 3 mm of aluminum, the half-value layer in aluminum for the remaining x rays was approximately 10 mm. The x-ray source allowed performance of biologic magnification radiography. Star-pattern tests indicated an equivalent focal spot size of less than 60 mum. Exposures of a single pulse could be obtained. The duration of a single x-ray pulse was estimated to be of the order of picoseconds. CONCLUSION. With use of subpicosecond laser pulses, x-ray generation can occur with a smaller equivalent focal spot size than with conventional x-ray sources.
|
|
| 26. |
- Hunsche, S, et al.
(författare)
-
Ionization and fragmentation of C-60 via multiphoton-multiplasmon excitation
- 1996
-
Ingår i: Physical Review Letters. - 1079-7114. ; 77:10, s. 1966-1969
-
Tidskriftsartikel (refereegranskat)abstract
- We study the intensity dependence of ionization and fragmentation of buckminsterfullerene (C-60) in strong laser fields. Our data provide strong evidence that at intensities less than or similar to 10(14) W/cm(2) these processes occur predominantly via multiphoton excitation of the 20 eV plasmon resonance of C-60 At least two plasmons have to be created to initiate fragmentation or multiple ionization.
|
|
| 27. |
- Johansson, S. G, et al.
(författare)
-
Comparison of New Experimental and Astrophysical F-values For Some Ru-ii Lines, Observed In Hst Spectra of Chi-lupi
- 1994
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 421:2, s. 809-815
-
Tidskriftsartikel (refereegranskat)abstract
- We report on experimental absolute oscillator strengths for 18 UV lines of Ru II, obtained by combining laser-induced fluorescence measurements of radiative lifetimes and branching fractions from line intensities in a calibrated Fourier-transform spectrum. HST/GHRS observations of the spectrum of the sharp-lined B star chi Lupi contain six of these lines, for which ''astrophysical'' relative f-values have been determined. The agreement is within 0.10 dex for a Ru abundance of log N(Ru)/N(H) = -7.90, which is 2.3 dex above the solar abundance.
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
- Ju, J., et al.
(författare)
-
Analysis of x-ray emission and electron dynamics in a capillary-guided laser wakefield accelerator
- 2014
-
Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:5
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of electron acceleration driven by laser wakefield inside a 30.5 mm long dielectric capillary tube is analyzed using radiation emitted in the x-ray range. 3D particle-in-cell simulations, performed with parameters close to the experimental ones, show that in long plasmas, the accelerated electrons catch up and finally overrun the driving laser owing to a higher velocity of the electrons in the plasma. The electrons are then transversely scattered by the laser pulse, and penetrate the capillary wall where they generate bremsstrahlung radiation, modeled using geant4 simulations. The signature of bremsstrahlung radiation is detected using an x-ray camera, together with the betatron radiation emitted during electron acceleration in the plasma bubble. The reflection of betatron radiation from the inner capillary surface also accounts for a fraction of the observed signal on the x-ray camera. The simulation results are in agreement with the experimental ones and provide a detailed description of the electron and radiation properties, useful for the design of laser wakefield accelerators or radiation sources using long plasma media.
|
|
