Comparative study of laser acceleration of thin foils at wavelengths 0.44 μm and 1.3μm

The acceleration of thin plastic foils irradiated with frequency-triplet ( λ = 0.44 μm) and fundamental ( λ = 1.3 μm) iodine laser light was investigated. Rear-side velocities and two-dimensional behaviour of the foils were recorded with a novel 6-frame photographic diagnostic. Core velocities were inferred from calorimetry and X-ray backlighting. Unlike at 1.3 μm, the rear-side and core velocities were found to be quite different at λ = 0.44 μm. An explanation is offered in terms of lack of lateral smoothing at 0.44 μm. The ablation pressure scales as P_abl≈ I^0.6_absλ ^-0.4.