Abstract

High harmonics generated with a femtosecond laser provides virtually all of the properties that one would wish to apply to photoemission investigations of electronic states in materials. Harmonic light is monochromatic and polarized, as determined by the input laser. It is tunable over a wide range of photon energies. For even modest input intensities (0.5 mJ per pulse in our system) we have been able to generate harmonics with useful fluxes to 80 eV. The generated harmonic light is co-linear with the input laser so that reflective optics such as normal or grazing incidence gratings of reasonable size can be used to collect and select a particular harmonic of interest and then refocus this light onto the material under study. With efficient electron detection schemes useful photoelectron count rates can be obtained. With these properties alone, harmonics makes possible photoelectron spectroscopy experiments in the laboratory setting that were previously the sole domain of large scale synchrotron labs. But an additional, and singularly important, aspect of harmonic light is its femtosecond, and possibly even attosecond, time structure which opens avenues for investigations of the temporal evolution of excited electronic systems.

© 1997 Optical Society of America