Chirped Multilayer Soft X-Ray Mirrors for Attosecond Soft X-Ray Pulses

Aperiodic XUV multilayer coatings with broad spectral bandwidth and flat dispersion characteristics have been developed and fabricated as reflecting and spectrally filtering optical elements for attosecond XUV pulses. Based on a genetic computational optimization algorithm aperiodic Mo/Si multilayer structures exhibiting up to 40 eV spectral bandwidth and pulse responses down to about 100 attoseconds at 80 eV center photon energy could be simulated. An experimental multilayer design exhibiting about 15 eV spectral bandwidth at 93 eV photon energy was realized and tested in an attosecond XUV pump – IR probe photoionization experiment (attosecond streak camera) utilizing single attosecond pulses from a High Harmonic Generation source. The results display the enhanced spectral bandwidth filtered by the aperiodic mirror which holds the potential for the extraction of single XUV pulses shorter than 200 attoseconds.