Development of a Tunable UV Laser System Synchronizing Precisely with Synchrotron Radiation Pulses from UVSOR

Abstract

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 monochromatized 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*(ls2p ip), produced by primary synchrotron radiation excitation.

Two-photon double-resonant excitation of the Xe* autoionization states using synchronized laser and synchrotron radiation pulses

“…by the precise control of the relative time delay between the two pulses. Complementary to other recent experiments using the laser for the 'pump' and the SR for the probe process (Gatzke et al 1995, Mizutani et al 1997, we have continued the study of highly excited states which are prepared ('pumped') initially by the SR (Meyer et al 1996). These latter experiments have to face low excitation rates, mainly caused by the lower spectral resolution of the SR or, in the case of inner-shell excitation, by much smaller cross sections.…”

Two-colour studies of the even-parity autoionization series 5p51/2nell′(ell = p, f) in atomic xenon

“…More recently this two-colour pump-probe technique has been applied to measurements of the total photoionization cross section of SRexcited Xe (nd, J = 1) levels in the range of np , nf ARS (Gisselbrecht et al 1998) as well as to the laser photoelectron spectroscopy of SR-excited Ar (ns, nd, J = 1) levels (Mitsuke et al 2000). In these experiments the SR was applied in the first excitation step and synchronization between the SR pulses and those of a mode-locked laser were used (Ederer et al 1992, Lacoursière et al 1994, Mizutani et al 1997 providing considerably higher efficiency in the two-photon process. In the case of the Xe * 5p 5 1/2 nf even parity ARS (Gisselbrecht et al 1998) the lineshape parameters have been successfully determined, whereas practically no signal due to Xe (np ) ARS were observed at their expected energy positions.…”

Combination of lasers and synchrotron radiation in studies of atomic photoionization

“…For some application a pulsed synchronized laser has been used [31][32][33]. Due to a much higher duty cycle, this combination of pulsed lasers and SR has shown its advantage especially for investigations of short-lived excited states and can be applied to time-resolved experiments in the picosecond regime.…”