Petawatt class laser optimization and ultrashort probe pulse generation for relativistic laser plasma interactions Advancements in high peak power laser development have resulted in laser systems capable of accelerating charged particles in a plasma to nearly the speed of light. For a comprehensive understanding and optimization of such interactions towards higher experimental yields further enhancements in the laser system performance are required along with a method that enables a direct view into the laser induced plasma with a high spatial and temporal resolution. The work presented in this thesis details the results of multiple investigations regarding upgrades to the petawatt class POLARIS laser and the development of a multi beam ultrashort laser system for probing relativistic laser plasma interactions at Friedrich Schiller University and Helmholtz Institute in Jena Germany.