DEVELOPMENT OF A TUNABLE UV LASER SYSTEM SYNCHRONIZING PRECISELY WITHSYNCHROTRON-RADIATION PULSES FROM UVSOR

A mode-locked Ti:sapphire laser is made to oscillate at the frequency of the UVSOR storage ring, 90.115 MHz, in a multi-bunch operation mode . The third harmonic of the laser is available in the wavelength range 243-280nm. Synchrotron radiation from an undulator is monochromatized by a grazing-incidence monochromator and introduced coaxially with th e laser. The temporal profile of the photon pulses is monitored in sit u by a luminescing substance/photomultiplier combination. The delay ti ming between the laser and synchrotron radiation can be changed from 0 to 11 ns by adjusting an electronic module that provides phase-locked loop stabilization of the laser pulse. The reliability and feasibilit y of this laser-synchrotron radiation combination technique are demons trated by applying pump-probe experiments to two physical systems. The first system is photodissociation of iodomethane (CH3I) with a laser photon, followed by photoionization of I and CH3 fragments with synchr otron radiation. The second, two-photon ionization of He atoms, is stu died as the prototype of a time-resolved experiment. The He+ signal co unts as a function of the laser-synchrotron radiation delay are found to be enhanced in a narrow time window, which can be interpreted in te rms of a short lifetime of the resonant state, He(1s2p P-1), produced by primary synchrotron radiation excitation.