Relativistic laser-solid interaction: from near-infrared to mid-infrared*

There has been growing interest in the physics and application of mid-infrared laser-plasma interactions. The ponderomotive potential in laser-plasma interactions increases with longer laser wavelength, so there may be significant differences in the physics of x-ray and electron generation and other phenomena driven by mid-infrared lasers. In this work, we report the results of experiments performed with millijoule, 40 fs, 2 µm laser pulses generated by an optical parametric amplifier (OPA) which are focused onto metallic and silicon targets. We characterize the hard x-ray source and electron source produced via both 2 µm and 800 nm driving laser in the same setup. Hard x-ray source size, energy efficiency, emission of k-alpha relative to bremsstrahlung, electron energy and beam divergence are studied and compared from near-infrared to mid-infrared.