CONSTRUCTION OF A TIME-FREQUENCY 2-DIMENSIONAL MULTIPLEX COHERENT ANTI-STOKES-RAMAN SCATTERING SPECTROMETER HAVING 15 PS TIME RESOLUTION

A picosecond time-resolved multiplex coherent anti-Stokes Raman scatte ring (CARS) spectrometer based on a new principle has been constructed using a femtosecond laser, nanosecond lasers, and a streak camera. Th e second harmonic of the output from the femtosecond Ti:sapphire oscil lator/regenerative-amplifier system is used for the photoexcitation. T he second harmonic of a nanosecond Nd:YLF laser is used as CARS probin g omega1 radiation, and the output of a nanosecond broadband dye laser is used as omega2 radiation. CARS signals, which are generated from t he sample during the nanosecond probing pulses, are analyzed in the fr equency domain by a spectrograph and are resolved in the time domain b y a streak camera. This enables us multiplex CARS measurements not onl y in the frequency domain but also in the time domain (termed two-dime nsional multiplex CARS). Consequently, CARS spectra at various delay t imes are obtainable with a single measurement. Owing to the short dura tion and high stability of the femtosecond pumping pulses, time resolu tion as high as 15 ps has been achieved. Picosecond time-resolved CARS spectra of all-trans retinal and beta-carotene are presented to demon strate the high capability of the constructed system. The factors whic h determine the time resolution of this CARS spectrometer are discusse d.