Ultrafast laser pulse stretching via dispersive materials including high dispersion orders

Abstract

Ultrafast laser systems typically employ complicated systems for varying their pulse length (duration) such as an ultrafast IR mode-locked laser used at the Schlesinger Compact Accelerator Center at Ariel University. The laser is an Astrella manufactured by Coherent generating an 800nm pulse. The pulse duration can be varied from 10 ps to 35 fs using a remote-controlled grating-based compressor. In order to measure the time duration of the pulse, an automated compact autocorrelator was designed and developed. The laser is mainly used to extract electrons from a photo-cathode using dual BBO frequency tripling system, providing a UV (266nm) ultra-short pulse. The electrons are formed into a beam, which is used to generate a THz FEL. Using an fs-level UV pulse, the extracted electron beam is unstable, resulting in high space-charge effects, high emittance values, and lowered radiation power dramatically. For this reason, we aim to stretch the UV pulse to a ps level. We study here an applicative method that uses dispersive materials. This method is convenient, compact, and can be easily installed. However, ultrafast lasers can suffer from high dispersion orders. Therefore, we study the contribution of the third and fourth orders of dispersion using analytical and numerical methods. Furthermore, our analysis takes into account the self-phase modulation effect when intense lasers are used. An experimental measurement is executed to confirm our numerical results, and a comparison between the experimental and simulation results is presented.