No abstract

We demonstrate the three-fold post-chirped-pulse-amplification (post-CPA) pulse compression of a high peak power laser pulse using allyl diglycol carbonate (CR39), which was selected as the optimal material for near-field self-phase modulation out of a set of various nonlinear plastic materials, each characterized with respect to its nonlinear refractive index and optical transmission. The investigated materials could be applied for further pulse compression at high peak powers, as well as for gain narrowing compensation within millijoule-class amplifiers. The post-CPA pulse compression technique was tested directly after the first CPA stage within the POLARIS laser system, with the compact setup containing a single 1 mm thick plastic sample and a chirped mirror pair, which enabled a substantial shortening of the compressed pulse duration and, hence, a significant increase in the laser peak power without any additional modifications to the existing CPA chain.

In multi mode optical fibers degenerated modes occur, which cannot be discriminated by their propagation properties. Hence, in principle any arbitrary superposition of these degenerated modes can be used to build an equivalent set of modes. In a perturbed system this degeneracy can be broken, and as a consequence -not every superposition represents real modes of the fiber. In mode division multiplexing system this leads to high inter-modal crosstalk, if unsuitable (initially degenerated) modes are chosen. Based on the analysis of the fiber's transmission matrix, we present a measurement scheme to prove degeneracy breaking and to identify physical non-degenerated modes.