The interaction of 100-fs Ti:sapphire laser pulses with thin foil targets was experimentally investigated at intensities exceeding 1018 W/cm2. High harmonics were observed in transmission through an overdense plasma in the direction of the incident beam. From the cutoff frequency of the harmonics an electron density of 1 × 1024 cm-3 is inferred, indicating a compression of the plasma by the ponderomotive force of the laser pulse.
© 1997 Optical Society of America
R. Hässner, W. Theobald, S. Niedermeier, H. Schillinger, and R. Sauerbrey, "High-order harmonics from solid targets as a probe for high-density plasmas," Opt. Lett. 22, 1491-1493 (1997)