Ion acceleration with a picosecond CO$_{2}$ laser

The ion acceleration experiment at BNL explores the laser wavelength scaling from optical to mid-IR region. 10$^{16}$ W/cm$^{2}$ of a CO$_{2}$ laser intensity focused on a 8 $\mu $m Al foil produced a 1-MeV proton beam. This observation agrees with predicted scaling of the proton energy E$_{p}\sim I^{1/2}$\textit{$\lambda $}. We now initiated new ion acceleration runs where a gas jet is a target. At the CO$_{2}$ laser wavelength (\textit{$\lambda $}=10 \textit{$\mu $}m), a critical plasma density is 100 times lower (10$^{19}$ cm$^{-3})$ than for a glass laser. This opens new opportunities for time-resolved interferometric optical diagnostic of over-critical laser/plasma interactions. We present the latest results from both foil and gas jet ion acceleration experiments and give an outlook on possibilities of attaining multi-terawatt femtosecond pulses with CO$_{2}$ lasers.