Phase Modulation of Intense Ultrashort Laser Pulses Reflected From Steep, Dense Plasmas

Abstract

The phase modulation of intense ( ${I=10\mathrm{}}^{18}\mathrm{W}/{\mathrm{cm}}^2$) ultrashort laser pulses ( ${\tau }_p=70\mathrm{}\mathrm{fs}$) after reflection from steep, dense plasmas has been temporally resolved for the first time in particle-in-cell simulations. The position of the turning point from where the pulse reflects has been compared to the phase modulation, over a range of angles of incidence. At normal incidence or $s$ polarization the phase modulation almost exactly represents the movement of the turning point due to the light pressure. As the angle of incidence is increased for $p$ polarization, the simple Fresnel relationship between phase modulation and displacement of the reflection position, $\Delta \phi \left(t\right){=-2k}_0\Delta x\left(t\right)\cos {\theta }_0$, increasingly breaks down.