Effect of relativistic plasma on extreme-ultraviolet harmonic emission from intense laser-matter interactions

Experiments were performed in which intense laser pulses (up to 9x10(19) W/cm(2)) were used to irradiate very thin (submicron) mass-limited aluminum foil targets. Such interactions generated high-order harmonic radiation (greater than the 25th order) which was detected at the rear of the target and which was significantly broadened, modulated, and depolarized because of passage through the dense relativistic plasma. The spectral modifications are shown to be due to the laser absorption into hot electrons and the subsequent sharply increasing relativistic electron component within the dense plasma.

Detection of short lived radioisotopes as a fast diagnostic for intense laser-solid interactions

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.

Observations of the filamentation of high-intensity laser-produced electron beams

Filamented electron beams have been observed to be emitted from the rear of thin solid targets irradiated by a high-intensity short-pulse laser when there is low-density plasma present at the back of the target. These. observations are consistent with a laser-generated beam of relativistic electrons propagating through the, target. which is subsequently fragmented by a Weibel-like instability in the low-density plasma at the. rear. These, measurements are in agreement with particle-in-cell simulations and theory, since the filamentation instability is predicted to be dramatically enhanced when the electron beam density approaches that of the background plasma.

High power laser production of short-lived isotopes for positron emission tomography

Positron emission tomography (PET) is a powerful diagnostic/imaging technique requiring the production of the short-lived positron emitting isotopes C-11, N-13, O-15 and F-18 by proton irradiation of natural/enriched targets using cyclotrons. The development of PET has been hampered due to the size and shielding requirements of nuclear installations. Recent results show that when an intense laser beam interacts with solid targets, megaelectronvolt (MeV) protons capable of producing PET isotopes are generated. This report describes how to generate intense PET sources of C-11 and F-18 using a petawatt laser beam. The work describing the laser production of F-18 through a (p,n) O-18 reaction, and the subsequent synthesis of 2-[F-18] is reported for the first time. The potential for developing compact laser technology for this purpose is discussed.

Laboratory measurements of 0.7 GG magnetic fields generated during high-intensity laser interactions with dense plasmas

We report measurements of ultrahigh magnetic fields produced during intense (similar to10(20) Wcm(-2) mum(2)) laser interaction experiments with solids. We show that polarization measurements of high-order vuv laser harmonics generated during the interaction (up to the 15th order) suggest the existence of magnetic field strengths of 0.7+/-0.1 GG in the overdense plasma. Measurements using higher order harmonics indicate that denser regions of the plasma can be probed. This technique may be useful for measurements of multi-GG level magnetic fields which are predicted to occur at even higher intensities.

Target charging effects on proton acceleration during high-intensity short-pulse laser-solid interactions

We report results from experiments performed at the Rutherford Appleton Laboratory using the VULCAN laser facility (I>5x10(19) W cm(-2)). Single wire targets were used, and on some shots additional objects were placed near the target. These were positioned so that they were not irradiated by the laser. Proton emission from single wire targets was observed as radially symmetric structures (

Measurements of relativistic self-phase-modulation in plasma

We report the first systematic observations of relativistic self-phase-modulation (RSPM) due to the interaction of a high intensity laser pulse with plasma. The plasma was produced in front of a solid target by the prepulse of a 100 TW laser beam. RSPM was observed by monitoring the spectrum of the harmonics generated by the intense laser pulse during the interaction. The multipeaked broadened spectral structure produced by RSPM was studied in plasmas with different density scale lengths for laser interactions at intensities up to 3.0x1019 W cm(-2) (a=p(osc)/m(e)c=4.7). The results are compared with calculated spectra and agreement is obtained.

Ultrahigh-intensity laser-produced plasmas as a compact heavy ion injection source

The possibility of using high-intensity laser-produced plasmas as a source of energetic ions for heavy ion accelerators is addressed. Experiments have shown that neon ions greater than 6 MeV can be produced from gas jet plasmas, and well-collimated proton beams greater than 20 MeV have been produced from high-intensity Laser solid interactions. The proton beams from the back of thin targets appear to be more collimated and reproducible than are high-energy ions generated in the ablated plasma at the front of the target and may be more suitable for ion injection applications. Lead ions have been produced at energies up to 430 MeV.

Imaging of high harmonic radiation emitted during the interaction of a 20 TW laser with a solid target

We present images of the source of extreme ultraviolet (XUV) harmonic emission at a wavelength of 220 Angstrom from the interaction of a 20 TW, 1.053 mu m Nd:glass laser beam focused to intensities up to 4x10(18) W cm(-2) onto a solid target. From these measurements we determine an upper limit to the source size and brightness of the harmonic emission to show its efficacy as a novel source of short-pulse, coherent XUV radiation. We also demonstrate the empirical scaling of the harmonic generation efficiency with irradiance up to 10(19) W mu m(2) cm(-2), and extrapolate to estimate the possible source brightness at higher irradiances. These source brightnesses are compared to those available from an x-ray laser system. (C) 1997 American Institute of Physics.

Measurements of the hole boring velocity from Doppler shifted harmonic emission from solid targets

The fast ignitor scheme for inertial confinement fusion requires forward driving of the critical density surface by light pressure (hole boring) to allow energy deposition close to the dense fuel. The recession velocity of the critical density surface has been observed to be nu/c = 0.015 at an irradiance of 1.0 x 10(19) W cm(-2) at a wavelength of 1.05 micron, in quantitative agreement with modeling. (C) 1996 American Institute of Physics.