Fast thickness measurements with frequency modulated continuous wave terahertz radiation

Broadband laser based terahertz systems for multilayer thickness inspections are getting established in industrial environments, such as in the quality control for paint processes in the automotive industry. Within this contribution we address another highly attractive and complementary industrial terahertz application by the thickness and density inspection of thick and multilayer plastics as for example in the field of tube production. In order to inspect plastic layers from millimeter to several tens of centimeters thickness at measurement rates of up to several kilohertz, we use electronic frequency modulated continuous wave terahertz systems operating in the terahertz regime below 500 GHz.