Ion acceleration in multispecies targets driven by intense laser radiation pressure (1207.4288v1)

Abstract: The acceleration of ions from ultra-thin foils has been investigated using 250 TW, sub-ps laser pulses, focused on target at intensities up to $3\times10^{20} \Wcm2$. The ion spectra show the appearance of narrow band features for proton and Carbon peaked at higher energy (in the 5-10 MeV/nucleon range) and with significantly higher flux than previously reported. The spectral features, and their scaling with laser and target parameters, provide evidence of a multispecies scenario of Radiation Pressure Acceleration in the Light Sail mode, as confirmed by analytical estimates and 2D Particle In Cell simulations. The scaling indicates that monoenergetic peaks with more than 100 MeV/nucleon energies are obtainable with moderate improvements of the target and laser characteristics, which are within reach of ongoing technical developments.

• The paper demonstrates that LS-mode radiation pressure accelerates ions from ultra-thin foils with a 250 TW laser system.
• It employs 2D PIC simulations and analytical models to elucidate the transition from Hole Boring to Light Sail acceleration.
• Scaling laws suggest achieving ion energies over 100 MeV/nucleon, opening pathways for compact ion sources in various applications.

Ion Acceleration in Multispecies Targets Driven by Intense Laser Radiation Pressure

This paper investigates ion acceleration from ultra-thin foils using intense laser radiation, focusing on a regime dominated by Radiation Pressure Acceleration (RPA) in the Light Sail (LS) mode. Employing a 250 TW laser system, the paper reports the acceleration of ions, particularly proton and carbon, from sub-micrometer targets at intensities reaching up to $3 \times 10^{20}~\text{W cm}^{-2}$. The research is significant in its observation of narrow-band ion spectral features, which contrast with the broad spectra typically associated with conventional mechanisms like Target Normal Sheath Acceleration (TNSA).

The experimental setup utilized the VULCAN laser system with capabilities extending to multi-hundred joule energy delivery in sub-picosecond pulses. A variety of targets composed of different materials and varying thicknesses were used. The ion spectra revealed prominently narrow peaks for proton and carbon ions in the 5-10 MeV/nucleon range, suggesting an RPA-dominated process. These features displayed a much higher particle flux than previously reported, which hints at the efficiency and potential of the LS mode in RPA for ion acceleration.

The paper employs both experimental and computational approaches to support its claims. The authors present 2D Particle In Cell (PIC) simulations that corroborate analytical estimates of ion behavior under intense radiation pressure. A key aspect explored is the transition from Hole Boring (HB) to LS acceleration. This transition ensures the entire laser-irradiated target region is efficiently accelerated forward as a single entity, conclusively supported both by analytical predictions and numerical simulations.

Scaling laws derived from the experimental data and analytical models suggest that ion energies exceeding 100 MeV/nucleon are feasible with appropriately adjusted target and laser parameters. This sets a promising direction for future experimental work aiming to leverage LS RPA for practical applications, such as hadron therapy.

The implications of this research extend to both theoretical and practical domains. Theoretically, it advances the understanding of laser-matter interactions at high intensities, particularly the dynamics of multi-species target compositions under extreme laser radiation. Practically, it suggests pathways for developing compact and efficient ion sources, potentially beneficial in scientific research, medical applications, and materials processing.

Future research directions might focus on optimizing target parameters and laser pulse shapes to enhance ion beam quality and reduce divergence further. Additionally, the combination of multi-dimensional PIC simulations with advanced experimental diagnostics could open new insights into consistently harnessing the full potential of LS-mode RPA.

In conclusion, this paper contributes valuable insights into ion acceleration mechanisms driven by intense laser radiation pressure, with a future outlook on achieving practical energy levels necessary for a range of applications. The coupling of experimental results with theoretical models offers a robust framework for understanding and further developing this technology.