Temporally and radially-resolved femtosecond optical measurements of solid density plasma reflectivities and transmissivities

We report on space and time-resolved femtosecond optical probing of a solid density hot plasma. The plasma is produced by 3 × 1015 W/cm2 intensity, 210 fs duration laser pulse irradiation of a transparent fused quartz solid target. Time-resolved measurements of reflectivity and transmissivity at the center of the plasma using a non-perturbative synchronized probe pulse incident from the rear side of the target show a rapid reflection enhancement and transmission decrease, attributed to formation of a super-critical density, steep-gradient plasma layer at the surface. The probe beam is also used to map relectivity and transmissivity at different locations from the plasma center with 20 μm resolution. The measurements indicate radially-dependent plasma characteristics and cooling times which will be discussed in light of a radially-dependent intensity of the pump laser.