Masakazu Mizutani

Development of a Tunable UV Laser System Synchronizing Precisely with Synchrotron 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 243-280 nm. Synchrotron radiation from an undulator is monochromated by a grazing-incidence monochromator and introduced coaxially with the laser. The temporal profile of the photon pulses is monitored in situ by a luminescing substance/photomultiplier combination. The delay timing 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 feasibility of this laser-synchrotron radiation combination technique are demonstrated by applying pump-probe experiments to two physical systems. The first system is photodissociation of iodomethane (CHA) with a laser photon, followed by photoionization of I and CH3 fragments with synchrotron radiation. The second, two-photon ionization of He atoms, is studied as the prototype of a time-resolved experiment. The He+ signal counts as a function of the laser-synchrotron radiation delay are found to be enhanced in a narrow time window, which can be interpreted in terms of a short lifetime of the resonant state, He*(1s2p 1P), produced by primary synchrotron radiation excitation.

Laser-induced fluorescence excitation spectroscopy of N2+ produced by VUV photoionization of N2 and N2O

Synchrotron radiation emitted from the UVSOR storage ring is monochromated by a grazing-incidence monochromator and introduced coaxially with the second harmonic of a mode-locked Ti:sapphire laser. Sample gases, N2 and N2O, are photoionized into vibronically ground N2+ with the fundamental light of the undulator radiation at 18.0 and 18.6 eV, respectively. Laser-induced fluorescence (LIF) excitation spectra of N2+ from N2 and N2O are measured in the laser wavelength region of the (B 2Σu+, v′ = 0) ← (X 2Σg+, v′′ = 0) transition at 389–392 nm. The LIF excitation spectra of N2+ exhibit two maxima due to the P and R branches in which rotational bands are heavily overlapped. The rotational temperature is determined by simulating an LIF excitation spectrum by using the theoretical intensity distribution of rotation bands convoluted with the spectral width of the laser.

Laser-induced fluorescence spectroscopy of CN(X2Σ+) radicals produced by vacuum UV photoexcitation of CH3CN with synchrotron radiation

Abstract Synchrotron radiation-pump and laser-probe spectroscopy is employed to observe CN radicals in the vibronically ground state produced from CH 3 CN. The photon energy of synchrotron radiation is changed from 13.6 to 18.6 eV. The laser-induced fluorescence signal is measured as a function of the photon energy with the laser wavelength fixed at the CN( B 2 Σ + , v B =0← X 2 Σ + , v X =0) transition. The onset of 15.4 eV of the fluorescence signal indicates that the detected CN( X 2 Σ + ) radicals result from dissociative ionization of CH 3 CN. The partial cross section for the formation of CN( X 2 Σ + ) is estimated to be 0.1–0.5 Mb and is compared with that for the CH 3 + formation.