SU‐GG‐T‐462: Observation of Quasi‐Monoenergetic Laser Accelerated Proton and Carbon Beams

• Published in: Medical Physics 2010-06, Vol.37 (6), p.3293-3293
• Main Authors: Litzenberg, D, Dollar, F, Bulanov, S, Brantov, A, Bychenkov, V, Chvykov, V, Kalintchenko, G, Matsuoka, T, McGuffey, C, Yanovsky, V, Krushelnick, K, Maksimchuk, A
• Format: Article
• Language: English
• Subjects: Carbon; Coulomb explosion; Laser materials; Mirrors; Optical dispersion; Particle‐in‐cell method; Proton therapy; Protons; Spontaneous emission; Therapeutics
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3468860

Purpose: To perform preliminary experiments to achieve the Directed Coulomb Explosion (DCE) regime of proton acceleration to therapeutic energies in high‐intensity laser‐matter interactions. Method and Materials: Particle‐in‐Cell (PIC) simulations of the planned experiments at HERCULES laser at the University of Michigan have predicted a new regime of attainable laser‐target interactions for proton acceleration. The laser was recently upgraded to 300 TW with Amplified Spontaneous Emission (ASE) intensity contrast ratio of 10−11, allowing intensities of 2×1022 W/cm2 to be achieved in a near diffraction limited, 1.3 micron, focal spot. Dual plasma mirrors have been installed and characterized to reduce the prepulse at < 30 ps (from the uncompensated dispersion of optical elements during the pulse compression) before the main pulse providing 3 orders of magnitude contrast improvement. This allowed experiments on thin foil membranes (50 nm) with 50TW temporally clean pulses without compromising the target. Results: We found for the first time that for all target thicknesses proton spectra exhibit quasi‐monoenergetic features, which are more pronounced for ultra‐thin (50 nm Si3N4) targets resulted in AE/E∼30%. Moreover for these Si3N4 targets spectra for all the charge states of carbon ions C3+‐C6+ are also found to be quasi‐monoenergetic. Maximum proton energy drops from 6 MeV for 1 ⌈ m Mylar foil to 4 MeV for 50 nm Si3N4 membranes. Conclusion: Implementation of dual plasma mirrors substantially improved laser contrast and created more favorable proton and carbon flux‐energy distributions. Further improvements to the plasma mirrors are required, using better antireflection coatings on glass substrates, to achieve the DCE regime of proton acceleration.