Abstract
An experimental study on high order harmonic generation (HHG) from the interaction of 45 fs Ti:sapphire laser pulses with preformed plasma plumes of nano-structured targets has been carried out. Highly efficient HHG in the range of 9(th) order to 19(th) order was observed. The stability of HHG from nano-structured targets is studied. Broadband HHG was observed from these targets. This spectral broadening can be understood from the self-modulation of the laser in the plasma of nano-structured targets. Efficient generation of even and odd order harmonics was observed through the use of two-color pulses. HHG from circularly polarized light was also observed from two color excitation. The observations can be explained qualitatively from symmetry breaking of high order harmonic generation through the introduction of second harmonic pulses.