Measurement of the polarization state of high harmonics generated in gases

We have measured the polarization of high harmonics of 785-nm Ti:sapphire radiation. The harmonics were generated in argon and nitrogen gas. When the driving field is elliptically polarized, there is, in general, an offset angle between the major axis of the driving field's polarization ellipse and the polarization of the harmonics. The ellipticity of the harmonic polarization is also generally different from that of the driving field. There are substantial differences in behavior between the two gases, particularly for harmonics whose energies lie close to the ionization potential. (C) 1996 Optical Society of America