Generation of Short Laser Pulses by Using Hollow Fibre and Chirped Mirror Compressor System

Abstract

A FEMTOLASERS hollow core silicon fibre of length 1 m and 250μm inner diameter was set up in the lab in Waterloo with the purpose of generating sub 10fs pulses for Coulomb Explosion Imaging (CEI). The input laser was a new Ti: sapphire regenerative amplifier system providing energy of 1mJ per pulse at a duration of the 35fs with 1kHZ repetition rate. Modifications to the initial setup were crucial in achieving the desired goal. A new, angled, incident window was made to eliminate reflective damage to the mirrors, and a new delivery beamline was built to minimize unwanted nonlinear effects. The pressure dependence of spectral broadening in argon gas was studied to find the best performance and found to be p=0.43atm. A chirped mirror system was set up to compensate the group delay dispersion in the beam line to the CEI experiment and compress the pulse, and MATLAB programs were written to carefully estimate how much material was necessary to minimise total dispersion of the system. The optimal input beam duration was determined by comparing the setting of the compressor with the output spectrum of the fibre and it was found that a spectrum capable of generating a 7.49fs laser pulse was produced if group delay dispersion and higher order dispersions were assumed to be zero. However, after calculating the higher order dispersion present in the system, which can not be compensated by the chirped mirrors, a laser pulse with a duration of 9.76fs is feasible with an average power of 0.45W. This result if verified by CEI will result in near equilibrium imaging of small molecules in the Waterloo lab for the first time.