High Absorption of Laser Light in Target Plasma with Plateau-Ramp Type Density Profile

The enhancement of resonance absorption in a laser-irradiated target plasma is ascertained by a numerical integration method for the fixed density profile which has a density plateau in front of the steep density gradient at the critical surface. It is shown that the interference between the laser light and the plasma wave excited near the critical surface in the target plasma plays an essential role in the enhancement of absorption. Conditions for enhancement are derived analytically with respect to the density gradient in the resonance region and the number density of plateau formed at the target surface. The results suggest that large absorption rates are retained during the laser irradiation to the target whose density profile is being modified.