Laser-induced continuum structure in the two ionization continua of xenon

Abstract

We report the observation of pronounced, spectrally narrow laser-induced continuum structures (LICS) in the two ionization continua of xenon. A nanosecond laser pulse with nearly transform-limited bandwidth induces a LICS by coupling the initially unpopulated ${5p}^{5}9p[1/2{]}_{0}$ state to the continuum. The LICS is probed by one-photon ionization of the ${5p}^{5}6p[1/2{]}_{0}$ state. This state is populated in an independent excitation step by an additional laser pulse acting prior to the probe and dressing pulses. The two ionization channels that leave the xenon ion in either the ${}^{2}{P}_{1/2}$ or the ${}^{2}{P}_{3/2}$ fine-structure state are detected separately by monitoring the kinetic energy of the photoelectrons in a time-of-flight electron spectrometer. A suppression of the photoelectron signal of up to 80% as compared to the far off resonance value is achieved. The line shapes reveal a Fano parameter close to zero. The LICS is identical for the coupling into the two continua. Therefore the branching ratio into the two ionization channels does not vary with the dressing-laser detuning for the coupling scheme implemented here.