Demonstration of pulse switching with > 1011 prepulse contrast by cascaded optical parametric amplification

Abstract

The use of chirped-pulse amplification (CPA) in high-energy systems allows the generation of high-peak power and ultrahigh intensity, and has led to intensities greater than 1020 W • cm-2 [1]-[3]. These systems are of especially high interest for exploring high-energy dense plasma physics and for fast ignition in inertial confinement fusion [4]. In these systems the control of the prepulses is crucial as their intensity might perturb the target before the main pulse arrives. Plasma generation thresholds of solid targets are generally of the order of 1010 W • cm-2 and hence require a contrast ratio exceeding 1010 for a 10 20 W • cm-2 system. Optical parametric chirped-pulse amplification (OPCPA), a CPA technique which relies on the three-wave mixing process in a nonlinear crystal, has received much attention due to its superior characteristics for broadband amplification in high-power laser system front-ends. In fact, OPCPA operated near degeneracy and thus providing high gain while maintaining broad spectral bandwidth is increasingly replacing Ti:sapphire front-ends in Nd:glass short-pulse lasers [5]-[8]. With respect to the prepulse contrast ratio, an OPCPA system offers enormous advantages. High-gain regenerative amplifiers usually produce a train of prepulses caused by the cavity leakage due to the limited extinction ratio of the intracavity polarizer, and they thus require additional postamplification temporal pulse cleaning techniques (e.g. [9],[10]). OPCPA amplifies only a single pulse out of the oscillator pulse train resulting in a prepulse contrast enhancement equal to the total saturated gain, provided that the pump pulse duration is sufficiently short so that there is no temporal overlap of the pump pulse with preceding or subsequent pulses. © 2007 Springer-Verlag New York.