Angle-Dependent High-Order Harmonic Generation from Aligned N<SUB>2</SUB> and O<I>2</I> Molecules

Abstract

This paper reports the results of high-order harmonic generation (HHG) observed by changing the angleαbetween polarization directions in the pump and probe experiment using high-intensity femtosecond laser pulses. Theα-dependent HHG from an ensemble of aligned O2 molecules was observed to be very similar to that from N2, being contrary to what was expected from the higher occupied molecular orbital of a single O2 molecule. It is shown that the characteristic angle dependence for O2 is due to low degree of alignment of molecules that can be achieved in the pump-probe experiment. The experimental results for N2 and O2 are in good agreement with those calculated using the recently developed theory. This demonstrates the validity of the theory in describing the characteristic properties of HHG from aligned N2 and O2.