High-order harmonic generation in molecular gases

We present an experimental study of harmonic generation in molecular gases, using the fundamental (800 nm) and the second harmonic (400 nm) of a 150 fs titanium-sapphire laser at an intensity of similar to 2 x 10(14) W cm(-2). We compare the conversion efficiency and the maximum energy obtained in different species: rare gases (Ar, Xe), diatomic molecules (N-2, H-2, O-2, CO) and polyatomic molecules (SF6, N2O, CO2, CH4, C3H8). The harmonic spectra from molecular gases are very similar to those obtained in the atomic gases, with a plateau and a cutoff whose location is strongly correlated to the value of the ionization potential. The conversion efficiency is not higher than that of the rare gases.