Phase modulation of intense ultrashort laser pulses reflected from steep, dense plasmas

The phase modulation of intense (I = 10(18) W/cm(2)) ultrashort laser pulse s (tau (p) = 70 fs) after reflection from steep, dense plasmas has: been te mporally resolved for the first time in particle-in-cell simulations. The p osition of the turning point from where the pulse reflects has been compare d to the phase modulation, over a range of angles of incidence. At normal i ncidence or s polarization the phase modulation almost exactly represents t he 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, Delt a phi (t) = -2k(0)Deltax(t) cos theta (0). increasingly breaks down.