New enhanced sensitivity infrared laser spectroscopy techniques applied to reactive plasmas and trace gas detection Infrared laser absorption spectroscopy (IRLAS) employing both tuneable diode and quantum cascade lasers (TDLs QCLs) has been applied with both high sensitivity and high time resolution to plasma diagnostics and trace gas measurements.TDLAS combined with a conventional White type multiple pass cell was used to detect up to 13 constituent molecular species in low pressure Ar H2 N2 O2 and Ar CH4 N2 O2 microwave discharges among them the main products such as H2O NH3 NO and CO HCN respectively. The hydroxyl radical has been measured in the mid infrared (MIR) spectral range in situ in both plasmas yielding number densities of between 1011 ... 1012 cm 3. Strong indications of surface dominated formation of either NH3 or N2O and NO were found in the H2 N2 O2 system. In methane containing plasmas a transition between deposition and etching conditions and generally an incomplete oxidation of the precursor were observed ... Quantenkaskadenlaser Plasma Wand Wechselwirkung Plasmachemie Cavity Ring Down Spektroskopie Infrarotabsorption Cavity Enhanced Absorptionsspektroskopie Quantum Cascade Laser Plasma Surface Interaction Plasma Chemistry Cavity Ring Down Spectroscopy Cavity Enhanced Absorption Spectroscopy