By tailoring short-wavelength harmonics generated by an ultrafast pulse passing through argon (Ar), researchers at the Foundation for Research and Technology-Hellas (Crete, Greece) have created a train of subfemtosecond pulses led by a single, strong pulse only 60 attoseconds (as) in duration. The optical spectrum of such a train of pulses is a series of harmonics spanning the 40—50-eV region and a coherent continuum background spanning 25—60 eV. The latter is associated with the single 60-as pulse. The filter used to tailor the harmonics was 150-nm-thick aluminum silicon (1%).
A Ti:sapphire laser supplied an 800-nm, 60-fs pulse that was then passed through an autocorrelator, creating two time-delayed pulses; these were focused into the exit pinhole of an Ar laminar-flow cell. A microchannel-plate detector acquired the signal exiting the filter. Intensity was measured as a function of time delay between the two pulses, producing an autocorrelation trace. The 60-as spike occurred at the region of strong overlap of the two 800-nm pulses. Such a short spike may someday allow the probing of electron motions in matter. Contact Nektarios Papadogiannis at [email protected].