Picosecond pulse radiolysis using femtosecond white light with a high S/N spectrum acquisition system in one beam shot

A stroboscopic, broad-spectrum (c.a. 500-830 nm) pulse radiolysis transient absorption detection system with a significantly improved signal-to-noise (S/N) ratio has been developed, enabling spectra to be recorded in as little as one electron beam shot. The white light continuum used as a probe was generated by focusing an 800-nm femtosecond laser pulse from a regenerative amplifier into a sapphire plate with high stability. Through a fast scanning technique that employs a charge-coupled detector (CCD), two sequential probe pulses whose time difference was ∼1 ms were successfully detected and used as the reference and signal light. This double pulse detection improved the intensity fluctuation of the probe, which is mainly a result of the long transport of the probe required to prevent radiation damage of the laser system. Time evolution of absorption spectra of hydrated electrons obtained by one delay scan is demonstrated to exhibit the capability of this system.