Plasma density oscillations (Langmuir waves) in the wake of an intense (Ipeak-3 x 1017W/cm2) laser pulse (100 fs) are measured with ultrafast time resolution using a longitudinal interferometric technique. Phase shifts consistent with large amplitude (Sne/ne-1) density waves at the electron plasma frequency were observed in a fully tunnel-ionized He plasma, corresponding to longitudinal electric fields of-10 GV/m. Strong radial ponderomotive forces enhance the density oscillations. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, , manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the *

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Synchronously pumped modelocked dye laser pumped by a frequencydoubled modelocked and Q switched diode laser pumped Nd:YAG laserWe have constructed a self-starting Kerr-lens mode-locked Ti:sapphire laser pumped synchronously by a mode-locked, LBO-doubled Nd:YAG laser. Using a home-built beam-pointing stabilizer, beam wander of the 532 nm pump is reduced by a factor of 25, thus enabling long term operation of TEMee nearly transform limited pulses with amplitude, repetition rate, and pulsewidth fluctuations comparable to or better than those of Ar-pumped Ti:Al,O, lasers. Interferometric autocorrelation using second harmonic in reflection from GaAs yielded a pulse width of 30 fs, limited by the dispersion of wide bandwidth cavity optics which permit tunability from 0.7 to 1.0 pm.