Efficient generation of sub-100 eV high-order harmonics from carbon molecules using infrared laser pulses

We demonstrate broad bandwidth and intense sub-100 eV high-order harmonics from diatomic carbon molecules driven by long-wavelength laser pulses. Up to now, one limitation of the intense carbon harmonic source driven by a 0.8 mu m wavelength Ti:sapphire laser has been the low cutoff around similar to 32 eV. In this paper, we show that this harmonic cutoff is extended to similar to 70 eV by increasing the driving laser wavelength to 1.71 mu m. Surprisingly, the carbon harmonic intensity is found to be high despite the long wavelength driving laser. Experiments show only similar to 30% decrease in the harmonic intensity when changing the driving laser wavelength from 0.8 mu m to 1.71 mu m. Such intense sub-100 eV coherent X-rays would have important applications in various domains of science and technology. (C) 2016 AIP Publishing LLC.