A femtosecond absorption spectrometer tunable from 50000 to 800 cm(-1): Nonlinear optics and pump/probe geometries

Solid state Ti:sapphire lasers were constructed and combined with nonlinear optics to produce a 100 fs resolution absorption spectrometer with tunability from 50 000 to 800 cm(-1) and <1 m o.d./s sensitivity. Tunable light generation and array detection technology are presented, including a discussion of the suitability of different infrared nonlinear optical materials. A systematic approach to stable infrared pulse generation is provided. Critical parameters of the pump/probe beam geometry are enumerated, revealing detrimental nonlinear contributions to the observed pump-induced change in probe absorbance. These effects include pump-induced probe phase modulation and pump-induced refractive index lenses. Measurements and simulations of the unwanted features in various system geometries reveal their systematic control and elimination. (C) 1996 American Institute of Physics.