Abstract

In the visible region of the spectrum, nonlinear conversion of light from one frequency to another is efficient because of phase matching. The phase velocity of the fundamental and nonlinear signal is matched such that the generated nonlinear signal sums coherently throughout the entire interaction region. At visible frequencies, this is accomplished by appropriate orientation of an anisotropic crystal. Alternatively, quasi-phase matching (QPM) techniques, which restrict nonlinear light generation to specific spatial regions, can be used. Both of these techniques rely on propagation effects. In this work, we present four new results. First, we present two new phase matching techniques that can be applied uniquely to extreme nonlinear optics, to upshift light into the XUV using high harmonic generation (HHG). The first uses a type of phase matching that can occur within single atoms. The second demonstrates a new type of QPM in the XUV based on amplitude modulation. We also show that these new techniques require an electron trajectory to be adjusted by 25 attoseconds. Finally, we demonstrate excellent agreement between theory and experiment for the first time in learningcontrol of high-order nonlinear processes.

© 2001 Optical Society of America