We present our recent experimental results of monoenergetic protons accelerated from the interaction of an intense terawatt CO2 laser pulse with a near-critical hydrogen gas target, with its density profile tailored by a hydrodynamic shock. A 5-ns Nd:YAG laser pulse is focused onto a piece of stainless steel foil mounted at the front edge of the gas jet nozzle orifice. The ablation launches a spherical shock into the near-critical gas column, which creates a sharp density gradient at the front edge of the target, with ~ 6X local density enhancement up to several times of critical density within ~<100 microns. With such density profile, we have obtained monoenergetic proton beams with good shot-to-shot reproducibility and energies up to 1.2 MeV.
Over the last two decades, BNL’s ATF has pioneered the use of high-peak power CO2 lasers for research in advanced accelerators and radiation sources. Our recent developments in ion acceleration, Compton scattering, and IFELs have further underscored the benefits from expanding the landscape of strong-field laser interactions deeper into the midinfrared (MIR) range of wavelengths. This extension validates our ongoing efforts in advancing CO2 laser technology, which we report here. Our next-generation, multi-terawatt, femtosecond CO2 laser will open new opportunities for studying ultra-relativistic laser interactions with plasma in the MIR spectral domain. We will address new regimes in the particle acceleration of ions and electrons, as well as the radiations sources, ranging from THz to gamma- rays, that are enabled by the emerging ultra-fast CO2 lasers.
Igor Pogorelsky, Mikhail Polyanskiy, Vitaly Yakimenko, Ilan Ben-Zvi, Peter Shkolnikov, Zulfikar Najmudin, Charlotte Palmer, Nicholas Dover, Piernicola Oliva, Massimo Carpinelli
Recent progress in using picosecond CO2 lasers for Thomson scattering and ion-acceleration experiments underlines
their potentials for enabling secondary radiation- and particle- sources. These experiments capitalize on certain
advantages of long-wavelength CO2 lasers, such as higher number of photons per energy unit, and favorable scaling of
the electrons' ponderomotive energy and critical plasma density. The high-flux x-ray bursts produced by Thomson
scattering of the CO2 laser off a counter-propagating electron beam enabled high-contrast, time-resolved imaging of
biological objects in the picosecond time frame. In different experiments, the laser, focused on a hydrogen jet, generated
monoenergetic proton beams via the radiation-pressure mechanism. The strong power-scaling of this regime promises
realization of proton beams suitable for laser-driven proton cancer therapy after upgrading the CO2 laser to sub-PW peak
power. This planned improvement includes optimizing the 10-μm ultra-short pulse generation, assuring higher
amplification in the CO2 gas under combined isotopic- and power-broadening effects, and shortening the postamplification
pulse to a few laser cycles (150-200 fs) via chirping and compression. These developments will move us
closer to practical applications of ultra-fast CO2 lasers in medicine and other areas.
The concept of a high-repetition-rate, high-average power γ-source is based on Compton backscattering from
the relativistic electron beam inside a picosecond CO2 laser cavity. Proof-of-principle experiments combined
with comput
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