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 nonl inear optics to produce a 100 fs resolution absorption spectrometer wi th tunability from 50 000 to 800 cm(-1) and <1 m o.d./s sensitivity. T unable light generation and array detection technology are presented, including a discussion of the suitability of different infrared nonlin ear optical materials. A systematic approach to stable infrared pulse generation is provided. Critical parameters of the pump/probe beam geo metry are enumerated, revealing detrimental nonlinear contributions to the observed pump-induced change in probe absorbance. These effects i nclude pump-induced probe phase modulation and pump-induced refractive index lenses. Measurements and simulations of the unwanted features i n various system geometries reveal their systematic control and elimin ation. (C) 1996 American Institute of Physics.