Theory and simulation of gain-guided noncollinear modes in chirped quasi-phase-matched optical parametric amplifiers

Chirped quasi-phase-matched (QPM) gratings offer essentially constant gain over wide bandwidths, making them promising candidates for short-pulse optical parametric amplifiers. However, we discovered that high- gain noncollinear processes can compete with the desired broadband gain of such amplifiers. Here, we investigate these noncollinear gain-guided modes both numerically and analytically, including longitudinal nonuniformity of the phase-matching profile, lateral localization of the pump beam, and the noncollinear propagation of the interacting waves.