An investigation of harmonic generation in liquid media with a mid-infrared laser

We present a harmonic generation experiment using liquid H(2)O and D(2)O interrogated by a mid-infrared, 3.66 mum, laser at a maximum intensity of 8x10(13) W/cm(2). The unique aspects of the experiment include the long wavelength and short (9 cycle-110 fs) pulse duration of the laser as well as the near-resonant excitation of the H(2)O and D(2)O vibrational modes. We observe up to the 13th harmonic order in H(2)O and intensity scaling is consistent with a direct perturbative process up to the 9th harmonic order. Phase matching and resonant absorption are unable to account for the observed differences in harmonic yields between samples.