High-dynamic-range Measurement Of Laser Pulse Contrast By Use Of A Plasmashuttered Jitter-free Streak Camera

Recently there has been significant progress in the development of high-repetition-rate, highpeak-power Tisapphire systems.' Recent experiments in high harmonic generation (HHG) have demonstrated that with sufficiently short laser pulses (-20 fs), laser energies of 2-10 mJ can be used to generate very high-order harmonics, with photon energy up to 240 eV.2,3 However, to date, the lasers used to generate very high-order harmonics have typically been low-repetition-rate (10 Hz) systems. A kHz repetition-rate laser with sufficient peak power for high-harmonic generation would result in a 100 times increase in x-ray flux, with vastly improved signal-tonoise ratios. In addition, other processes such as low-order harmonic generation in gases4 become even more efficient with millijoules of laser energy. Thermal lensing is the main obstacle to scaling ultrafast Tisapphire systems to high average power, because the thermal time constant for sapphire is tens of milliseconds. If the focal length of the thermal lens is longer than the Rayleigh range in a focused beam, as it is in oscillators and low average power amplifiers ( < O S mJ compressed), the lensing effect is not ~ t r o n g . ~ However, with the larger beam sizes found in power amplifiers, thermal lensing compensation is critical. We have developed a Tisapphire amplifier system that generates a peak power of 0.125 TW, at 1-kHz repetition rate, with 2.5 mJ of energy, in a 20-fs pulse duration. The first stage is a ring multipass amplifier, which has been demonstrated previously.' It is pumped by 9 mJ from an intracavity doubled Nd:YLF laser (Quantronix 527). The second stage has a similar design to the first stage, and is pumped