High power lasers have been adapted to material processing, energy, military and medical applications. In the Laser Plasma Laboratory at CREOL, UCF, high power lasers are used to produce highly ionized plasmas to generate EUV emission. This thesis examines the quality of a recently acquired high power thin disk laser through thermal modeling and beam parameter measurements. High power lasers suffer from thermally induced issues which degrade their operation. Thin disk lasers use an innovative heat extraction mechanism that eliminates the transverse thermal gradient within the gain medium associated with thermal lensing. A thorough review of current thin disk laser technology is described. Several measurement techniques were performed on a high power thin disk laser. The system efficiencies, spectrum, and temporal characteristics were examined. The laser was characterized in the far-field regime to determine the beam quality and intensity of the laser. Laser cavity simulations of the thin disk laser were performed using LASCAD. The induced thermal and stress effects are demonstrated. Simulated output power and efficiency is compared to those that have been quantified experimentally.