Design and simulation of excitation laser system for <Emphasis Type="Italic">in-situ</Emphasis> Raman monitoring

A system for in-situ Raman monitoring of thin film growth during Microwave Plasma Assisted Chemical Vapour Deposition (μPACVD) process was developed. Dedicated Raman probe system was designed for precise focusing of an excitation laser beam into the growing film. The probes have to be placed outside the reaction chamber (working distance about 20 cm) in order to avoid interference of the process by work of measurement devices (non-invasive measurements). Analysis and calculation supported by simulations based on Monte-Carlo ray-tracing method and Beam Propagation Method showed that glancing-incidence optical configuration is of the Raman system is the most sufficient one. Range of the most effective incidence angles of the excitation beam was determined. Shape and size of laser spot at the sample was determined. Correction of spherical aberrations by use of doublets was proposed to ensure efficient focusing of the excitation beam into the investigated film.