Supercontinuum generation via in-situ femtosecond-laser-induced filamentation for ultrabroadband femtosecond/picosecond coherent Raman spectroscopy

Abstract

For thermometry and concentration measurements in the gas-phase two-beam hybrid femtosecond/picosecond (fs/ps) coherent Raman spectroscopy (CRS) is the benchmark. To acquire additional information on major combustion species like for example carbon dioxide, oxygen and molecular hydrogen a supercontinuum is required. In this work in-situ femtosecond-laser-induced filamentation is proposed. This is a non-linear optical process where the pulse self-focusses. Through self-phase modulation and non-linear dispersion in the plasma medium a supercontinuum is created. In-situ generation of the supercontinuum allows for a great simplification of the experimental setup as no additional chirped mirrors are required to deliver a near-transform-limited ultrabroadband pulse to the probe volume. The work presents an experimental campaign split into three phases to characterise the filamentation process, the probe volume dimensions, and the effects of the filamentation process on thermometry.