Enhanced harmonic generation in metallic funnels driven by short-wave infrared lasers

The enhancement effects of an intense short-wavelength infrared laser field in a single micrometer-scale metal funnel were observed in harmonic generation experiments. Low-order harmonics were generated by interacting 32-fs pulses centered at the 2.2-µm wavelength with gases in the funnel structures. The driving laser was an optical parametric amplifier operating at 60-kHz repetition rate. When the peak intensity of the laser beam at the entry of the funnel reached 9.1TW/cm2, third-order harmonic signals were detected. The low limits of the enhancement of the driving laser intensity in 10- and 15-µm funnels were estimated to be 32.4 and 20.8, respectively.