High harmonic generation in ethylene with infrared pulses

We produce harmonics in the molecule ethylene ðC2H4Þ with two different wavelengths and three pulse durations. Due to the low ionization potential ðIp 1⁄4 10:5 eVÞ of C2H4, longer wavelengths are needed to extend the maximum photon energy produced. Our results show that regardless of the strong dependence of the efficiency of the harmonic generation process with wavelength, at 1820 nm the cutoff observed is larger than that obtained with 800 nm, 15 fs pulses. We obtain harmonics with energies exceeding 70 eV at 9:0 10 W=cm2 with a 73 fs 1820 nm pulse. Under these circumstances, the limiting factor for the further extension of the cutoff seems to be the photoionization cross section of the