The ability to focus laser light to higher intensities is a major driver for light-matter interaction studies. For decades, the fundamental limitation on laser peak power has been the damage threshold and optical quality degradation of the laser-amplifying media. Technology overcame this limit with the invention of Chirped Pulse Amplification (CPA), allowing for ever- higher laser intensities (as shown in the Figure) to be generated on a compact scale.

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The idea behind CPA is portrayed in the figure. A mode-locked laser system generates an ultra-short (few-fs) low energy pulse. The pulse is then passed through a set of dispersive optics that stretches the pulse to a few ns duration, significantly lowering its peak power. This pulse can then be amplified using one of the various methods. After amplification, the final optic components disperse the pulse in a reverse manner, compressing the pulse back to the fs-level. The result is an orders-of-magnitude gain in peak power.

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New regimes of laser-matter interaction are now accessible with CPA lasers (indicated in the figure). Our research focus is on the relativistic regime, which is characterized by the high electron quiver energies of up to a few MeV, gained in the 1010-1012 V/cm electric fields at the focus of the laser. These energies far exceed the electron rest mass and so electrons in the plasma formed by the laser may become relativistic nearly instantaneously.