| 1. |
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| 2. |
- Genoud, Guillaume, et al.
(author)
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XUV digital in-line holography using high-order harmonics
- 2008
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 90:3-4, s. 533-538
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Journal article (peer-reviewed)abstract
- Abstract in Undetermined A step towards a successful implementation of time-resolved digital in-line holography with extreme ultraviolet (XUV) radiation is presented. Ultra-short XUV pulses are produced as high-order harmonics of a femtosecond laser and a Schwarzschild objective is used to focus harmonic radiation at 38 nm and to produce a strongly divergent reference beam for holographic recording. Experimental holograms of thin wires are recorded and the objects reconstructed. Descriptions of the simulation and reconstruction theory and algorithms are also given. Spatial resolution of a few hundreds of nanometers is potentially achievable, and the micrometer resolution range is demonstrated.
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| 3. |
- Svanberg, Sune, et al.
(author)
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Applications of terawatt lasers
- 1994
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In: LASER SPECTROSCOPY - XITH INTERNATIONAL CONFERENCE. - : AIP. - 1551-7616 .- 0094-243X. - 1563962624 ; :290, s. 264-269
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Conference paper (peer-reviewed)
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| 4. |
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| 5. |
- Abdulhadi, Nadia, et al.
(author)
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Patient-provider interaction from the perspectives of type 2 diabetes patients in Muscat, Oman : a qualitative study
- 2007
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In: BMC Health Services Research. - : Springer Science and Business Media LLC. - 1472-6963. ; 7, s. 162-
-
Journal article (peer-reviewed)abstract
- Background: Patients' expectations and perceptions of the medical encounter and interactions are important tools in diabetes management. Some problems regarding the interaction during encounters may be related to a lack of communication skills on the part of either the physician or the patient. This study aimed at exploring the perceptions of type 2 diabetes patients regarding the medical encounters and quality of interactions with their primary health-care providers. Methods: Four focus group discussions ( two women and two men groups) were conducted among 27 purposively selected patients ( 13 men and 14 women) from six primary health-care centres in Muscat, Oman. Qualitative content analysis was applied. Results: The patients identified some weaknesses regarding the patient-provider communication like: unfriendly welcoming; interrupted consultation privacy; poor attention and eye contact; lack of encouraging the patients to ask questions on the providers' side; and inability to participate in medical dialogue or express concerns on the patients' side. Other barriers and difficulties related to issues of patient-centeredness, organization of diabetes clinics, health education and professional competency regarding diabetes care were also identified. Conclusion: The diabetes patients' experiences with the primary health-care providers showed dissatisfaction with the services. We suggest appropriate training for health-care providers with regard to diabetes care and developing of communication skills with emphasis on a patient-centred approach. An efficient use of available resources in diabetes clinics and distributing responsibilities between team members in close collaboration with patients and their families seems necessary. Further exploration of the providers' work situation and barriers to good interaction is needed. Our findings can help the policy makers in Oman, and countries with similar health systems, to improve the quality and organizational efficiency of diabetes care services.
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| 6. |
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| 7. |
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| 8. |
- Albert, F, et al.
(author)
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Laser produced X-ray source in the 10-60 keV range at 1 kHz. Modified irradiation schemes in order to reach medical imaging quality
- 2001
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In: Journal de Physique IV. - : EDP Sciences. - 1155-4339. ; 11:PR2, s. 429-432
-
Journal article (peer-reviewed)abstract
- By tightly focusing ultra-short pulses from a Ti:sapphire terawatt laser onto a high-Z metallic target, hard x-ray pulses of short duration are produced. In most of our previous work concerning x-rays, a 150 mJ laser pulse with a 110 A duration has been used. Using mostly tin and tantalum targets, hard x-rays in the 10-60 keV range have been produced and used in differential absorption imaging around the K-alpha absorption edge of a contrast agent and also in imaging employing gated viewing for suppression of scattered radiation. In order to increase the x-ray yield (shortening the acquisition time) an increase in the laser repetition rate is desirable while still staying in the K-alpha energy regime. We have used a I kHz repetition-rate laser delivering 35 fs pulses in order to work towards these goals. We have clear evidence of hard x-ray generation above 30 keV, even for low laser pulse energies. We also studied the effect of a fs prepulse. The medical imaging capability of the source was explored. The use of a prepulse has been optimized in order to improve the image quality as well as the overall x-ray generation yield.
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| 9. |
- Altucci, C, et al.
(author)
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Frequency-resolved time-gated high-order harmonics
- 1998
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In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 58:5, s. 3934-3941
-
Journal article (peer-reviewed)abstract
- We report measurements of high-order harmonic spectra obtained with a 800-nm 150-fs loser pulse with a time-varying degree of ellipticity. The modulation of the polarization in time is achieved by using birefringent optics and self-phase modulation in a glass plate. We can create one or two temporal gates of a few femtoseconds width, during which the polarization is linear and harmonic emission is efficient. The harmonic spectra observed experimentally demonstrate that harmonics generated with linear polarization are frequency chirped. The values measured experimentally are consistent with theoretical predictions based on the strong field approximation. [S1050-2947(98)05511-5].
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| 10. |
- Altucci, C, et al.
(author)
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Influence of atomic density in high-order harmonic generation
- 1996
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In: Optical Society of America. Journal B: Optical Physics. - 0740-3224. ; 13:1, s. 148-156
-
Journal article (peer-reviewed)abstract
- We have investigated how high-order harmonics generated in rare gases depend on the atomic density. The peak and the profile of the atomic density in the interaction region were measured as a function of the backing pressure and the distance from the nozzle by a differential interferometry technique, The conversion efficiency for the harmonics in the plateau was found to increase approximately quadratically over the entire range of peak pressures investigated (3-80 mbar). The intensity of the harmonics in the cutoff region, in contrast, increased only until an optimum peak pressure was reached, beyond which it decreased. This optimum peak pressure was found to be dependent on both the laser intensity and the process order. To understand this effect, we have performed extensive propagation calculations of both the fundamental and the harmonic fields, using ionization rates and dipole moments from a tunnel ionization model. We obtained good agreement with the experimental results. The observed effect is attributed to ionization-induced defocusing of the fundamental laser beam, which reduces the peak intensity obtained in the medium and shortens the extent of the plateau. (C) 1996 Optical Society of America
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| 11. |
- An, W. W., et al.
(author)
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Synthesis and surface characteristics of CeTbO3+delta induced by femtosecond laser irradiation
- 2007
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In: Applied Surface Science. - : Elsevier BV. - 1873-5584 .- 0169-4332. ; 253:8, s. 3884-3887
-
Journal article (peer-reviewed)abstract
- This work describes the use of focused, high-intensity light from a Ti: sapphire laser that generates femtosecond pulses to irradiate mixture of CeO2 and Tb4O7 under ambient conditions. The prepared samples were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). XRD and XPS measurement results demonstrated that solid solution CeTbO3+delta with cubic fluorite structure has been synthesized on the irradiated target surface. SEM micrographs showed that the ultra-short laser irradiation resulted in the formation of foamy structure and spherical particles with size varying from about 30 to 200 nm. The formation mechanism has been discussed in detail. (c) 2006 Elsevier B.V. All rights reserved.
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| 12. |
- Andreev, N. E., et al.
(author)
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Analysis of laser wakefield dynamics in capillary tubes
- 2010
-
In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 12
-
Journal article (peer-reviewed)abstract
- A general approach to the modifications of the spectrum of a laser pulse interacting with matter is elaborated and used for spectral diagnostics of laser wakefield generation in guiding structures. Analytical predictions of the laser frequency red shift due to the wakefield excited in a capillary waveguide are confirmed by self-consistent modeling results. The role of ionization blue shift, and nonlinear laser pulse and wakefield dynamics on the spectrum modification, is analyzed for recent experiments on plasma wave excitation by an intense laser pulse guided in hydrogen-filled glass capillary tubes up to 8 cm long. The dependence of the spectral frequency shift, measured as a function of filling pressure, capillary tube length and incident laser energy, is in excellent agreement with the simulation results, and the associated longitudinal accelerating field is in the range 1-10 GV m(-1).
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| 13. |
- Assmann, R. W., et al.
(author)
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EuPRAXIA Conceptual Design Report
- 2020
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In: European Physical Journal: Special Topics. - : Springer Science and Business Media LLC. - 1951-6355 .- 1951-6401. ; 229:24, s. 3675-4284
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Journal article (peer-reviewed)abstract
- This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years. © 2020, The Author(s).
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| 14. |
- Aurand, Bastian, et al.
(author)
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A setup for studies of laser-driven proton acceleration at the Lund Laser Centre
- 2015
-
In: Laser and Particle Beams. - 0263-0346. ; 33:1, s. 59-64
-
Journal article (peer-reviewed)abstract
- We report on a setup for the investigation of proton acceleration in the regime of target normal sheath acceleration. The main interest here is to focus on stable laser beam parameters as well as a reliable target setup and diagnostics in order to do extensive and systematic studies on the acceleration mechanism. A motorized target alignment system in combination with large target mounts allows for up to 340 shots with high repetition rate without breaking the vacuum. This performance is used to conduct experiments with a split mirror setup exploring the effect of spatial and temporal separation between the pulses on the acceleration mechanism and on the resulting proton beam.
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| 15. |
- Batani, D., et al.
(author)
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Effects of laser prepulse on proton generation
- 2010
-
In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 620:1, s. 76-82
-
Conference paper (peer-reviewed)abstract
- Low-intensity laser prepulse ( < 10(13) W/cm(2), ns duration) are a major issue in experiments on laser-generation of protons, often limiting the performances of proton sources produced by high-intensity lasers (approximate to 10(19) W/cm(2), ps or fs duration) Several effects are associated to the prepulse and are discussed in this contribution: i) Destruction of thin foil targets by the shock generated by the laser prepulse ii) Creation of preplasma on target front side affecting laser absorption iii) Deformation of target rear side iv) Whole displacement of thin foil targets affecting focusing condition In particular, we show that under oblique high-intensity irradiation and for low prepulse intensities, the proton beam is directed away from the target normal. Deviation is towards the laser forward direction, with an angle that increases with the level and duration of the ASE pedestal. Also, for a given laser pulse, beam deviation increases with proton energy. The observations are discussed in terms of Target Normal Sheath Acceleration, in combination with a laser-controllable shock wave locally deforming the target surface. (C) 2010 Elsevier B.V. All rights reserved.
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| 16. |
- Batani, D., et al.
(author)
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Effects of laser prepulse on proton generation
- 2010
-
In: Radiation Effects and Defects in Solids. - : Informa UK Limited. - 1042-0150 .- 1029-4953. ; 165:6-10, s. 794-802
-
Conference paper (peer-reviewed)abstract
- Prepulse is a major issue for laser generation of protons, often limiting the performances of laser sources. Here, we show the use of prepulse (1013W/cm2, ns duration) to actively manipulate the proton beam direction. Under oblique high-intensity irradiation (approximate to 1019W/cm2, ps duration) of the thin foil target, and for low prepulse intensities, the proton beam is directed away from the ounperturbedo target normal. Observations are discussed in terms of target normal sheath acceleration, in combination with a laser-controllable shock locally deforming the target surface.
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| 17. |
- Bellini, M, et al.
(author)
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Temporal coherence of ultrashort high-order harmonic pulses
- 1998
-
In: Physical Review Letters. - 1079-7114. ; 81:2, s. 297-300
-
Journal article (peer-reviewed)abstract
- We have studied the temporal coherence of high-order harmonics (up to the 15th order) produced by focusing 100 fs laser pulses into an argon gas jet. We measure the visibility of the interference fringes, produced when two spatially separated harmonic sources interfere in the far field, as a function of the time delay between the two sources. In general, we find long coherence times, comparable to the expected pulse durations of the harmonics. For some of the harmonics, the interference pattern exhibits two regions, with significantly different coherence times. These results are interpreted in terms of different electronic trajectories contributing to harmonic generation. [S0031-9007(98)05569-7].
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| 18. |
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| 19. |
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| 20. |
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| 21. |
- Blagoev, K, et al.
(author)
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Radiative lifetimes of 6sns S-3(1) and 6snd D-3(1) excited states of HgI
- 2002
-
In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 66:3
-
Journal article (peer-reviewed)abstract
- Natural radiative lifetimes have been measured along the 6sns S-3(1) (n=7-10) and 6snd D-3(1) (n=6-11) Rydberg series of neutral mercury using time-resolved laser-induced fluorescence spectroscopy in a laser-produced mercury plasma. The states of Hg I investigated in the present work were populated from the ground state by a stepwise excitation process. Relativistic Hartree-Fock calculations, including intravalence interactions and core-polarization effects, have been performed and the theoretical lifetimes have been compared with the measurements.
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| 22. |
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| 23. |
- Borgstrom, S, et al.
(author)
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Time-resolved x-ray spectroscopy of optical-field-ionized plasmas
- 1995
-
In: Laser and Particle Beams. - 0263-0346. ; 13:4, s. 459-468
-
Journal article (peer-reviewed)abstract
- The time-dependent soft X-ray emission of helium and nitrogen plasmas generated by optical-field ionization is reported. The experiments were carried out by focusing pulses of the high-power Ti:sapphire laser of the Lund Institute of Technology (lambda = 796 nm, pulse duration 150 fs, pulse energy 150 mJ) to a 50-mu m diameter spot close to a nozzle, using He and N-2 as target gases. The emission on He+, N4+, and N3+ resonance lines was recorded by means of a flat-field grating spectrometer coupled to an X-ray streak camera. A pronounced difference in the temporal shape of the emission of the Lyman-alpha line of hydrogen-like helium and of the 2p-3d resonance lines of lithium-like and beryllium-like nitrogen was observed. The helium line exhibited an initial spike followed by a slow revival of the emission, whereas the nitrogen lines showed a slow decay after a fast initial rise. These observations are explained with the help of simulations.
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| 24. |
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| 25. |
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| 26. |
- Brenner, C. M., et al.
(author)
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Dependence of laser accelerated protons on laser energy following the interaction of defocused, intense laser pulses with ultra-thin targets
- 2011
-
In: Laser and Particle Beams. - 0263-0346. ; 29:3, s. 345-351
-
Journal article (peer-reviewed)abstract
- The scaling of the flux and maximum energy of laser-driven sheath-accelerated protons has been investigated as a function of laser pulse energy in the range of 15-380 mJ at intensities of 10(16)-10(18) W/cm(2). The pulse duration and target thickness were fixed at 40 fs and 25 nm, respectively, while the laser focal spot size and drive energy were varied. Our results indicate that while the maximum proton energy is dependent on the laser energy and laser spot diameter, the proton flux is primarily related to the laser pulse energy under the conditions studied here. Our measurements show that increasing the laser energy by an order of magnitude results in a more than 500-fold increase in the observed proton flux. Whereas, an order of magnitude increase in the laser intensity generated by decreasing the laser focal spot size, at constant laser energy, gives rise to less than a tenfold increase in observed proton flux.
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| 27. |
- Burza, Matthias, et al.
(author)
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Hollow microspheres as targets for staged laser-driven proton acceleration
- 2011
-
In: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 13, s. 013030-
-
Journal article (peer-reviewed)abstract
- A coated hollow core microsphere is introduced as a novel targetin ultra-intense laser–matter interaction experiments. In particular, it facilitates staged laser-driven proton acceleration by combining conventional target normal sheath acceleration (TNSA), power recycling of hot laterally spreading electrons and staging in a very simple and cheap target geometry. During TNSA of protons from one area of the sphere surface, laterally spreading hot electrons form a charge wave. Due to the spherical geometry, this wave refocuses on the opposite side of the sphere, where an opening has been laser micromachined.This leads to a strong transient charge separation field being set up there, which can post-accelerate those TNSA protons passing through the hole at the right time. Experimentally, the feasibility of using such targets is demonstrated. A redistribution is encountered in the experimental proton energy spectra, as predicted by particle-in-cell simulations and attributed to transient fields set up by oscillating currents on the sphere surface.
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| 28. |
- Burza, Matthias, et al.
(author)
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Laser wakefield acceleration using wire produced double density ramps
- 2013
-
In: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 16:1
-
Journal article (peer-reviewed)abstract
- A novel approach to implement and control electron injection into the accelerating phase of a laser wakefield accelerator is presented. It utilizes a wire, which is introduced into the flow of a supersonic gas jet creating shock waves and three regions of differing plasma electron density. If tailored appropriately, the laser plasma interaction takes place in three stages: Laser self-compression, electron injection, and acceleration in the second plasma wave period. Compared to self-injection by wave breaking of a nonlinear plasma wave in a constant density plasma, this scheme increases beam charge by up to 1 order of magnitude in the quasimonoenergetic regime. Electron acceleration in the second plasma wave period reduces electron beam divergence by approximate to 25%, and the localized injection at the density downramps results in spectra with less than a few percent relative spread. DOI: 10.1103/PhysRevSTAB.16.011301
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| 29. |
- Cacciani, P, et al.
(author)
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Isotope dependent predissociation in the C-1 Sigma(+) ,v=0 and v=1 states of CO
- 2001
-
In: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060. ; 15:1, s. 47-56
-
Journal article (peer-reviewed)abstract
- Rotationally resolved spectral lines in the C-X(1,0) band of carbon monoxide are investigated under high resolution using a coherent vacuum ultraviolet laser source, continuously tunable near 107 nm. Transition frequencies are determined by calibrating against a reference standard of iodine lines, recorded with saturation spectroscopy in the visible range, yielding an absolute accuracy of 0.003 cm(-1) in the vacuum ultraviolet. Improved molecular constants for the excited state are clarified and Mo effects of perturbation are found at the present level of accuracy. Line broadening measurements result in information on the excited state lifetime of the (CC)-C-1 Sigma (+),v = 1 state fur five natural isotopomers: of cal bon monoxide: tau((CO)-C-12-O-17) = 280 ps, tau((CO)-C-12-O-18) = 210 ps. tau((CO)-C-13-O-16) = 295 ps, tau((OO)-O-13-O-17) = 160 ps and tau((CO)-C-13-O-18) = 150 Ps. Within the accuracy of the present measurements: Ilo effects: of J-dependent lifetimes: were observed, for neither of the isotopomers. In addition direct time domain measurements: of the lifetime of the C(1)Sigma (+),v = 0 and v = 1 states of the main isotopomer are performed ill a pump-mode experiment using a picosecond VUV-laser, yielding tau((CO)-C-12-O-16) = 1780 ps for v = 0 and tau((CC)-C-12-C-16)) = 625 ps for v = 1. For C(1)Sigma (+), v = 0 in (CO)-C-12-O-16 and (CO)-C-13-O-16 the same lifetime is found; this lifetime matches experimental values of the oscillator strength and hence supports previous results showing pure radiative decay ill this state; the error margins however do not exclude some low level of predissociation. The measurements indicate that the C(1)Sigma (+),v = 0 state of the (CO)-C-13-O-18 isotopomer is predissociated with an estimated yield of 17% (i.e. above the level of predissociation for (CO)-C-12-O-16.) From the combined data predissociation yields: upon excitation of the C(1)Sigma (+),v = 1 state are derived, lying in the range 0.84-0.91. for the five less abundant isotopomers; for the main (CO)-C-12-O-16 isotopomer a strongly deviating predissociation yield of 0.65 is deduced.
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| 30. |
- Cacciani, P, et al.
(author)
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Lifetime measurements of the E (1)Pi, upsilon=0 and upsilon=1 states of (CO)-C-12-O-16, (CO)-C-13-O-16, and (CO)-C-13-O-18
- 1998
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X. ; 499
-
Journal article (peer-reviewed)abstract
- In a laboratory investigation using tunable picosecond lasers in a pump-probe configuration, lifetimes of the E (II)-I-1, v = O and v = 1 states of CO are experimentally determined. For E (II)-I-1, v = 1, the lifetime is found to vary significantly for the isotopomers. Combining the data with existing oscillator strengths, predissociation probabilities within the range of 93.6%-98.64% result for (CO)-C-12-O-16, (CO)-C-13-O-16, and (CO)-C-13-O-18 in, the case of the E (II)-I-1, v=1 state, which is the state that predominantly influences the isotopic fractionation of CO in interstellar clouds.
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| 31. |
- Cacciani, P, et al.
(author)
-
Predissociation of the 4p pi L-1 Pi Rydberg state of carbon monoxide
- 2002
-
In: Chemical Physics. - 0301-0104. ; 282:1, s. 63-73
-
Journal article (peer-reviewed)abstract
- Time-domain and frequency-domain spectroscopic experiments have been performed on the (4ppi)L(1)Pi, v = 0 Rydberg state in three isotopomers of carbon monoxide. Accurate values for the excited state lifetimes of the f-parity components have been determined: tau((CO)-C-12-O-16) = 1.08 +/- 0.05 ns, tau((CO)-C-13-O-16) = 72 +/- 10 ps and tau((CO)-C-13-O-18) = 29 +/- 6 ps. The spectral resolution in the frequency-domain experiment goes as far as the limit imposed by the natural lifetime; Q-branch lines, or f-parity components of the heavier isotopes, are resolved for the first time. Highly accurate transition frequencies are determined in a molecular beam experiment using comparison and interpolation with a saturated iodine reference standard. The results reveal a number of perturbations and predissociation mechanisms, displaying a high degree of complexity in the energetic region of the 4p Rydberg states of CO with strong isotopic effects. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 32. |
- Cantono, Giada, et al.
(author)
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Laser-driven proton acceleration from ultrathin foils with nanoholes
- 2021
-
In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 11:1
-
Journal article (peer-reviewed)abstract
- Structured solid targets are widely investigated to increase the energy absorption of high-power laser pulses so as to achieve efficient ion acceleration. Here we report the first experimental study of the maximum energy of proton beams accelerated from sub-micrometric foils perforated with holes of nanometric size. By showing the lack of energy enhancement in comparison to standard flat foils, our results suggest that the high contrast routinely achieved with a double plasma mirror does not prevent damaging of the nanostructures prior to the main interaction. Particle-in-cell simulations support that even a short scale length plasma, formed in the last hundreds of femtoseconds before the peak of an ultrashort laser pulse, fills the holes and hinders enhanced electron heating. Our findings reinforce the need for improved laser contrast, as well as for accurate control and diagnostics of on-target plasma formation.
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| 33. |
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| 34. |
- Carlsson, J, et al.
(author)
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Time-resolved Studies of Light-propagation In Paper
- 1995
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In: Applied Optics. - 2155-3165. ; 34:9, s. 1528-1535
-
Journal article (peer-reviewed)abstract
- A method for time-resolved recording of light scattering in thin, highly scattering media is described. Subpicosecond pulses from a high-power Ti:sapphire laser are used, and single-shot recordings of the scattered light are made with a fast streak camera. The method is applied to the study of light scattering in paper, and a 1-ps resolution is demonstrated. The dependence of the light scattering on the basis of weight and density of the paper has been studied. A white-light continuum generated from the high-power pulses by the use of self phase modulation in water is used to study the wavelength dependence of the scattering process. A model for the propagation of light in paper has been developed and used in Monte Carlo simulations. The experimental results are used for testing this model, and absorption and scattering parameters are determined from that comparison.
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| 35. |
- Carroll, DC, et al.
(author)
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Active manipulation of the spatial energy distribution of laser-accelerated proton beams
- 2007
-
In: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 76:065401(R), s. 1-065401
-
Journal article (peer-reviewed)abstract
- The spatial energy distributions of beams of protons accelerated by ultrahigh intensity (>10^19 W/cm2) picosecond laser pulse interactions with thin foil targets are investigated. Using separate, low intensity (<10^13 W/cm2) nanosecond laser pulses, focused onto the front surface of the target foil prior to the arrival of the high intensity pulse, it is demonstrated that the proton beam profile can be actively manipulated. In particular, results obtained with an annular intensity distribution at the focus of the low intensity beam are presented, showing smooth proton beams with a sharp circular boundary at all energies, which represents a significant improvement in the beam quality compared to irradiation with the picosecond beam alone.
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| 36. |
- Carroll, D. C., et al.
(author)
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A modified Thomson parabola spectrometer for high resolution multi-MeV ion measurements-Application to laser-driven ion acceleration
- 2010
-
In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 620:1, s. 23-27
-
Conference paper (peer-reviewed)abstract
- A novel Thomson parabola ion spectrometer design is presented, in which a gradient electric field configuration is employed to enable a compact design capable of high resolution measurements of ion energy and charge-to-mass ratio. Practical issues relating to the use of the spectrometer for measurement of ion acceleration in high-power laser-plasma experiments are discussed. Example experimental results for ion acceleration from petawatt-class laser interactions with thin gold target foils are presented. (C) 2010 Elsevier B.V. All rights reserved.
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| 37. |
- Carroll, David C., et al.
(author)
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Dynamic control and enhancement of laser-accelerated protons using multiple laser pulses
- 2009
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In: Comptes Rendus. Physique. - : Elsevier BV. - 1631-0705. ; 10:2-3, s. 188-196
-
Journal article (peer-reviewed)abstract
- The use of schemes involving multiple laser pulses to enhance and control the properties of beams of protons accelerated in ultra-intense laser irradiation of planar foil targets is discussed. Specifically, the schemes include the use of a second laser pulse to produce and control preplasma expansion of the target to enhance energy coupling to the proton beam; the use of a second laser pulse to drive shock deformation of the target to change the direction of the proton beam; and a scheme involving dual high intensity laser pulses to change the properties of the sheath field, with the aim of modifying the proton energy spectrum. An overview of our recent experimental and theoretical results is given. The overall aim of this work is to determine the extent to which the properties of the sheath-accelerated proton beam can be optically controlled, to enable beam delivery at high repetition rates. To cite this article: D.C. Carroll et al., C. R. Physique 10 (2009). (C) 2009 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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| 38. |
- Cassou, K., et al.
(author)
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Optimization toward a high-average-brightness soft-x-ray laser pumped at grazing incidence
- 2007
-
In: Optics Letters. - 0146-9592. ; 32:2, s. 139-141
-
Journal article (peer-reviewed)abstract
- We report the near-field imaging characterization of a 10 Hz Ni-like 18.9 nm molybdenum soft-x-ray laser pumped in a grazing incidence pumping (GRIP) geometry with a table-top laser driver. We investigate the effect of varying the GRIP angle on the spatial behavior of the soft-x-ray laser source. After multiparameter optimization, we were able to find conditions to generate routinely a high-repetition-rate soft-x-ray laser with an energy level of up to 3 mu J/pulse and to 6 x 10(17) photons/s/mm(2)/mrad(2)/(0.1% bandwidth) average brightness and 1 x 10(28) photons/s/mm(2)/mrad(2)/(0.1% bandwidth) peak brightness. (c) 2006 Optical Society of America.
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| 39. |
- Clarke, R. J., et al.
(author)
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Detection of short lived radioisotopes as a fast diagnostic for intense laser-solid interactions
- 2006
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:14
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Journal article (peer-reviewed)abstract
- As a diagnostic of high-intensity laser interactions (> 10(19) W cm(-2)), the detection of radioactive isotopes is regularly used for the characterization of proton, neutron, ion, and photon beams. This involves sample removal from the interaction chamber and time consuming post shot analysis using NaI coincidence counting or Ge detectors. This letter describes the use of in situ detectors to measure laser-driven (p,n) reactions in Al-27 as an almost real-time diagnostic for proton acceleration. The produced Si-27 isotope decays with a 4.16 s half-life by the predominantly beta+ emission, producing a strong 511 keV annihilation peak. (c) 2006 American Institute of Physics.
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| 40. |
- Coury, M., et al.
(author)
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Influence of laser irradiated spot size on energetic electron injection and proton acceleration in foil targets
- 2012
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:7
-
Journal article (peer-reviewed)abstract
- The influence of irradiated spot size on laser energy coupling to electrons, and subsequently to protons, in the interaction of intense laser pulses with foil targets is investigated experimentally. Proton acceleration is characterized for laser intensities ranging from 2 x 10(18) - 6 x 10(20) W/cm(2), by (1) variation of the laser energy for a fixed irradiated spot size, and (2) by variation of the spot size for a fixed energy. At a given laser pulse intensity, the maximum proton energy is higher under defocus illumination compared to tight focus and the results are explained in terms of geometrical changes to the hot electron injection. (C) 2012 American Institute of Physics. [doi:10.1063/1.3685615]
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| 41. |
- Coury, M., et al.
(author)
-
Injection and transport properties of fast electrons in ultraintense laser-solid interactions
- 2013
-
In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:4
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Journal article (peer-reviewed)abstract
- Fast electron injection and transport in solid foils irradiated by sub-picosecond-duration laser pulses with peak intensity equal to 4 x 10(20)W/cm(2) is investigated experimentally and via 3D simulations. The simulations are performed using a hybrid-particle-in-cell (PIC) code for a range of fast electron beam injection conditions, with and without inclusion of self-generated resistive magnetic fields. The resulting fast electron beam transport properties are used in rear-surface plasma expansion calculations to compare with measurements of proton acceleration, as a function of target thickness. An injection half-angle of similar to 50 degrees - 70 degrees is inferred, which is significantly larger than that derived from previous experiments under similar conditions. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4799726]
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| 42. |
- Dalui, Malay, et al.
(author)
-
Influence of micromachined targets on laser accelerated proton beam profiles
- 2018
-
In: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 60:3
-
Journal article (peer-reviewed)abstract
- High intensity laser-driven proton acceleration from micromachined targets is studied experimentally in the target-normal-sheath-acceleration regime. Conical pits are created on the front surface of flat aluminium foils of initial thickness 12.5 and 3 μm using series of low energy pulses (0.5-2.5 μJ). Proton acceleration from such micromachined targets is compared with flat foils of equivalent thickness at a laser intensity of 7 ×1019 W cm-2. The maximum proton energy obtained from targets machined from 12.5 μm thick foils is found to be slightly lower than that of flat foils of equivalent remaining thickness, and the angular divergence of the proton beam is observed to increase as the depth of the pit approaches the foil thickness. Targets machined from 3 μm thick foils, on the other hand, show evidence of increasing the maximum proton energy when the depths of the structures are small. Furthermore, shallow pits on 3 μm thick foils are found to be efficient in reducing the proton beam divergence by a factor of up to three compared to that obtained from flat foils, while maintaining the maximum proton energy.
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| 43. |
- Delfin, C, et al.
(author)
-
Influence of laser pulse duration on relativistic channels
- 2002
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 9:3, s. 937-940
-
Journal article (peer-reviewed)abstract
- A high-power (10 TW) laser is employed to generate relativistic channels in an underdense plasma. The lengths of the channels are measured by imaging the Thomson-scattered light, and the gas densities are determined through the forward Raman scattered light. The laser-pulse parameters are varied and their impact on the channel formation is studied. It is found that increasing the laser pulse duration in many cases produces longer channels, even as this implies reducing the laser peak power. A theoretical discussion is presented, proposing an explanation of the experimental results. (C) 2002 American Institute of Physics.
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| 44. |
- Delfin, C, et al.
(author)
-
Influence of the medium length on high-order harmonic generation
- 1999
-
In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 32:22, s. 5397-5409
-
Journal article (peer-reviewed)abstract
- We study high-order harmonic generation using a 110 fs Ti:sapphire laser loosely focused into a variable-length gas cell filled with neon or argon at 5 mbar pressure. The harmonic intensity is recorded as a function of the medium length, varying between 2 and 21 mm. Several cases are examined, the 17th and the 29th harmonic in argon, and the 29th and 51st harmonic in neon, at the same intensity 4 x 10(14) W cm(-2). We find that the length which maximizes the harmonic yield varies from 10 mm to more than 20 mm. We discuss the different effects affecting the photon yield of the high-order harmonics.
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| 45. |
- Descamps, D, et al.
(author)
-
Extreme ultraviolet interferometry measurements with high-order harmonics
- 2000
-
In: Optics Letters. - 0146-9592. ; 25:2, s. 135-137
-
Journal article (peer-reviewed)abstract
- We demonstrate that high-order harmonics generated by short, intense laser pulses in gases provide an interesting radiation source for extreme ultraviolet interferometry, since they are tunable, coherent, of short pulse duration, and simple to manipulate. Harmonics from the 9th to the 15th are used to measure the thickness of an aluminum layer. The 11th harmonic is used to determine the spatial distribution of the electron density of a plasma produced by a 300-ps laser. Electronic densities higher than 2-10(20) electrons/cm(3) are measured. (C) 2000 Optical Society of America. OCIS codes: 190.0190, 190.4160, 190.7110, 120.3180, 140.7240, 350.4500.
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| 46. |
- Descamps, D, et al.
(author)
-
Two- and three-photon ionization of rare gases using femtosecond harmonic pulses generated in a gas medium
- 2001
-
In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 64:3
-
Journal article (peer-reviewed)abstract
- The fifth harmonic of a 60-fs 10-Hz terawatt titanium:sapphire laser generated in Xe gas is used to ionize Xe and Kr atoms by nonresonant two-photon absorption and At atoms through a quasiresonant three-photon process. At relatively low harmonic yields, the variation of the number of Kr and Xe ions with the number of harmonic photons is quadratic. At high harmonic yields, it deviates from a quadratic behavior, which we attribute to the influence of ionization in the harmonic process distorting the harmonic wave front. The two-photon ionization cross sections in Xe and Kr at 160 nm are found to be comparable.
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| 47. |
- Desforges, F. G., et al.
(author)
-
Analysis of Electron Injection in Laser Wakefield Acceleration Using Betatron Emission in Capillary Tubes
- 2015
-
In: Laser Acceleration of Electrons, Protons, and Ions III; and Medical Applications of Laser-Generated Beams of Particles III. - : SPIE. - 1996-756X .- 0277-786X. ; 9514, s. 95140-95140
-
Conference paper (peer-reviewed)abstract
- The dynamics of ionization-induced electron injection in the high density (similar to 1.2 x 10(19)cm(-3)) regime of Laser Wakefield Acceleration (LWFA) was investigated by analyzing betatron X-ray emission inside dielectric capillary tubes. A comparative study of the electron and betatron X-ray properties was performed for both self-injection and ionization-induced injection. Direct experimental evidence of early onset of ionization-induced injection into the plasma wave was obtained by mapping the X-ray emission zone inside the plasma. Particle-In-Cell (PIC) simulations showed that the early onset of ionization-induced injection, due to its lower trapping threshold, suppresses self-injection of electrons. An increase of X-ray fluence by at least a factor of two was observed in the case of ionization-induced injection due to an increased trapped charge compared to self-injection mechanism.
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| 48. |
- Desforges, F. G., et al.
(author)
-
Dynamics of ionization-induced electron injection in the high density regime of laser wakefield acceleration
- 2014
-
In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 21:12
-
Journal article (peer-reviewed)abstract
- The dynamics of ionization-induced electron injection in high density (similar to 1.2 x 10(19) cm(-3)) regime of laser wakefield acceleration is investigated by analyzing the betatron X-ray emission. In such high density operation, the laser normalized vector potential exceeds the injection-thresholds of both ionization-injection and self-injection due to self-focusing. In this regime, direct experimental evidence of early on-set of ionization-induced injection into the plasma wave is given by mapping the X-ray emission zone inside the plasma. Particle-In-Cell simulations show that this early on-set of ionization-induced injection, due to its lower trapping threshold, suppresses the trapping of self-injected electrons. A comparative study of the electron and X-ray properties is performed for both self-injection and ionization-induced injection. An increase of X-ray fluence by at least a factor of two is observed in the case of ionization-induced injection due to increased trapped charge compared to self-injection mechanism. (C) 2014 AIP Publishing LLC.
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| 49. |
- Desforges, F. G., et al.
(author)
-
Reproducibility of electron beams from laser wakefield acceleration in capillary tubes
- 2014
-
In: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 740, s. 54-59
-
Journal article (peer-reviewed)abstract
- The stability of accelerated electron beams produced by self injection of plasma electrons into the wakefield driven by a laser pulse guided inside capillary tubes is analyzed statistically in relation to laser and plasma parameters, and compared to results obtained in a gas jet. The analysis shows that reproducible electron beams are achieved with a charge of 66 pC +/- 11%, a FWHM beam divergence of 9 mrad +/- 14%, a maximum energy of 120 MeV +/- 10% and pointing fluctuations of 2.3 mrad using 10 mm long, 178 mu m diameter capillary tubes at an electron density of (10.0 +/- 1.5) x 10(18) cm(-3). Active stabilization of the laser pointing was used and laser parameters were recorded on each shot. Although the shot-to-shot laser energy fluctuations can account for a fraction of the electrons fluctuations, gas density fluctuations are suspected to be a more important source of instability. (C) 2013 Elsevier B.V. All rights reserved.
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| 50. |
- Dromey, B, et al.
(author)
-
Picosecond metrology of laser-driven proton bursts.
- 2016
-
In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
-
Journal article (peer-reviewed)abstract
- Tracking primary radiation-induced processes in matter requires ultrafast sources and high precision timing. While compact laser-driven ion accelerators are seeding the development of novel high instantaneous flux applications, combining the ultrashort ion and laser pulse durations with their inherent synchronicity to trace the real-time evolution of initial damage events has yet to be realized. Here we report on the absolute measurement of proton bursts as short as 3.5±0.7 ps from laser solid target interactions for this purpose. Our results verify that laser-driven ion acceleration can deliver interaction times over a factor of hundred shorter than those of state-of-the-art accelerators optimized for high instantaneous flux. Furthermore, these observations draw ion interaction physics into the field of ultrafast science, opening the opportunity for quantitative comparison with both numerical modelling and the adjacent fields of ultrafast electron and photon interactions in matter.
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