| 51. |
- Norin, Johan, et al.
(författare)
-
Time-frequency characterization of femtosecond extreme ultraviolet pulses.
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 88:19, s. 193901-193901
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Tidskriftsartikel (refereegranskat)abstract
- We present energy-resolved cross-correlation measurements of an extreme ultraviolet (XUV) pulse, generated as the fifth harmonic (15.5 eV) of an intense 80 fs laser pulse centered at 400 nm. Spectrally resolving the cross-correlation signal allows us to characterize the time-dependent frequency of the XUV pulse. We find that the fifth harmonic has a small negative chirp in excess of that predicted by perturbation theory. In addition, by manipulating the chirp of the driving laser we can induce and measure a positive or a negative chirp on the XUV pulse.
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| 52. |
- Osvay, Karoly, et al.
(författare)
-
On the temporal contrast of high intensity femtosecond laser pulses
- 2005
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Ingår i: Laser and Particle Beams. - 0263-0346. ; 23:3, s. 327-332
-
Tidskriftsartikel (refereegranskat)abstract
- The temporal contrast is classified into two main regimes, the nanosecond-scale and the picosecond-scale contrast prior to the main pulse. The Lund terawatt laser system is shown to be improved on the nano- and picosecond-scale by a factor of 10 and 50, respectively, when it was optimized for contrast but not for energy. Calculations are also presented to emphasize the role of angular dispersion on the picosecond contrast. Finally we show a compromise between the duration and contrast of femtosecond laser pulses amplified in an optical parametric (chirped pulse) amplifier.
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| 53. |
- Permogorov, Alexander, et al.
(författare)
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Effects of pulse chirp on laser-driven proton acceleration
- 2022
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- Optimisation and reproducibility of beams of protons accelerated from laser-solid interactions require accurate control of a wide set of variables, concerning both the laser pulse and the target. Among the former ones, the chirp and temporal shape of the pulse reaching the experimental area may vary because of spectral phase modulations acquired along the laser system and beam transport. Here, we present an experimental study where we investigate the influence of the laser pulse chirp on proton acceleration from ultrathin flat foils (10 and 100 nm thickness), while minimising any asymmetry in the pulse temporal shape. The results show a ± 10 % change in the maximum proton energy depending on the sign of the chirp. This effect is most noticeable from 10 nm-thick target foils, suggesting a chirp-dependent influence of relativistic transparency.
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| 54. |
- Svanberg, Sune, et al.
(författare)
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Generation, characterization, and medical utilization of laser-produced emission continua
- 2000
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Ingår i: Laser and Particle Beams. - 0263-0346. ; 18:3, s. 563-570
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Tidskriftsartikel (refereegranskat)abstract
- Intense continua of electromagnetic radiation of very brief duration are formed in the interaction of focused ultra-short terawatt laser pulses with matter. Two different kinds of experiments, which have been performed utilizing the Lund 10 Hz titanium-doped sapphire terawatt laser system are being described, where visible radiation and X-rays, respectively, have been generated. Focusing into water leads to the generation of a light continuum through self-phase modulation. The propagation of the light through tissue was studied addressing questions related to optical mammography and specific chromophore absorption. When terawatt laser pulses are focused onto a solid target with high nuclear charge Z, intense X-ray radiation of few ps duration and with energies exceeding hundreds of keV is emitted. Biomedical applications of this radiation are described, including differential absorption and gated-viewing imaging.
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| 55. |
- Svanberg, Sune, et al.
(författare)
-
Lund High-power Laser Facility - Systems and 1st Results
- 1994
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 49:2, s. 187-197
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Tidskriftsartikel (refereegranskat)abstract
- A high-power laser facility has been established at the Lund Institute of Technology, Sweden, available to national groups and their international collaboration partners. The laboratory incorporates three major 10 Hz laser systems, that can be operated individually or synchronized in combined use. Each system represents extreme optical powers in a certain sense. The main system is a terawatt laser based on chirped pulse amplification in titanium doped sapphire. It generates radiation tunable in the 760-840 nm region with a maximum power of 1.5TW in 150 fs long pulses. A further system is set up to generate nanosecond pulses of extremely bright VUV radiation (down to 120 nm) by sum-difference four-wave mixing in krypton gas. Finally, a third system generates widely tunable radiation (200-900 nm) of a pulse duration of 10's of picoseconds. The experimental areas incorporate target chambers, spectrometers and fast electronics. The systems have been used in a number of experiments requiring high optical powers, and a brief account of the initial activities is given. Detailed studies of high-harmonic generation in inert gases are reported as well as the generation and application of hard X-rays from microplasmas. Intense white-light generation by self-phase modulation in water has been used for biological tissue studies and for chemical pump/probe experiments. VUV radiation has been used for studies of radiative properties of excited states of free atoms. Finally, the picosecond laser system has been utilized in studies of the temporal structure of harmonics from an inert gas and for soft X-ray generation for high-resolution microscopy. A discussion section concludes the presentation.
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| 56. |
- Tillman, C, et al.
(författare)
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Imaging Using Hard X-rays From A Laser-produced Plasma
- 1995
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Ingår i: Applied Physics B. - 0946-2171. ; 61:4, s. 333-338
-
Tidskriftsartikel (refereegranskat)abstract
- Imaging of technical and biological objects using hard X-rays from a laser-produced plasma source is demonstrated. Magnification radiography and single-shot imaging of biological samples are feasible with the source, which utilised focused radiation from a short-pulse terawatt laser. Differential imaging with element specificity and a new projection geometry for X-ray radiography are proposed.
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| 57. |
- Wahlström, Claes-Göran, et al.
(författare)
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High-order Harmonic-generation In Rare-gases With An Intense Short-pulse Laser
- 1993
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 48:6, s. 4709-4720
-
Tidskriftsartikel (refereegranskat)abstract
- We present experimental studies of high-order harmonic generation in the rare gases performed with a short-pulse titanium sapphire laser operating at 794 nm in the 10(14)-10(15) W/cm2 range. The harmonic yields generated in neon and in argon are studied for all orders as a function of the laser intensity. They vary first rather steeply, in the cutoff region, then much more slowly in the plateau region, and, finally, they saturate when the medium gets ionized. The dependence of the high-order harmonic cutoff with the laser intensity in neon and argon is found to be lower than that predicted in single-atom theories. We observe high-order harmonics in argon and xenon (up to the 65th and 45th, respectively) at 10(15) W/cm2, which we attribute to harmonic generation from ions. We also show how the harmonic and fundamental spectra get blueshifted when the medium becomes ionized.
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| 58. |
- Wahlström, Claes-Göran, et al.
(författare)
-
Supersonic jets of hydrogen and helium for laser wakefield acceleration
- 2016
-
Ingår i: Physical Review Accelerators and Beams. - 2469-9888. ; 19
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of laser wakefield accelerated electrons in supersonic gas flows of hydrogen and helium are investigated. At identical backing pressure, we find that electron beams emerging from helium show large variations in their spectral and spatial distributions, whereas electron beams accelerated in hydrogen plasmas show a higher degree of reproducibility. In an experimental investigation of the relation between neutral gas density and backing pressure, it is found that the resulting number density for helium is ∼30% higher than for hydrogen at the same backing pressure. The observed differences in electron beam properties between the two gases can thus be explained by differences in plasma electron density. This interpretation is verified by repeating the laser wakefield acceleration experiment using similar plasma electron densities for the two gases, which then yielded electron beams with similar properties.
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| 59. |
- Wojda, F., et al.
(författare)
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Laser-driven plasma waves in capillary tubes
- 2009
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Ingår i: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 80:6
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Tidskriftsartikel (refereegranskat)abstract
- The excitation of plasma waves over a length of up to 8 cm is demonstrated using laser guiding of intense laser pulses through hydrogen-filled glass capillary tubes. The plasma waves are diagnosed by spectral analysis of the transmitted laser radiation. The dependence of the spectral redshift-measured as a function of filling pressure, capillary tube length, and incident laser energy-is in excellent agreement with simulation results. The longitudinal accelerating field inferred from the simulations is in the range of 1-10 GV/m.
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