Increasing laser intensities predictably led to new regimes of light-matter interaction, with yet unrealized applications. For decades, the fundamental limitations on reaching higher laser peak power arose from the damage thresholds and optical quality degradation of laser-amplifying media. The breakthrough was the invention of Chirped Pulse Amplification (CPA), a technique for amplifying an ultrashort laser pulse up to the petawatt level.

The term “laser contrast” describes the intensity ratio between the peak of the pulse and light arriving few ps ahead. It has been shown in many studies that a high laser contrast plays a crucial role in providing efficient particle acceleration.[1]

I will present a contrast enhancement system which realizes an ultrafast optical switch. This switch is based on reflection from a flat, transient plasma surface, known as a plasma mirror (PM).[2]

PMs are based on the ultrafast ionization by laser light. The laser pulse is focused on a flat transparent target, at a well determined spot size. The fluence is sufficiently low for the leading prepulses to be transmitted through the target, yet becoming high enough for the striking edge of the main pulse to ionize it. Owing to the very fast ionization, a dense, highly reflective plasma layer is triggered on the surface of the target. Thus it remains a flat, metal-like mirror with good optical quality, low divergence, and highly reflective for the main pulse.

[1] Ceccotti, T., et al. "Proton acceleration with high-intensity ultrahigh-contrast laser pulses." Physical review letters 99.18 (2007): 185002.‏

[2] Doumy, G. et al. "Complete characterization of a plasma mirror for the production of high-contrast ultraintense laser pulses". Phys. Rev. E 69, 026402. (2004)