Optical Parametric Amplification via Difference Frequency

Conventionally, broadband frequency conversion is achieved through spontaneous parametric down conversion. Such a process requires a pump source with frequencies higher than the targeted frequencies. This presents the limitation for light generation in the ultraviolet regime. Here, we present a different approach for optical parametric amplification using a difference-frequency pump. The prerequisite for optical amplification is complex-valued nonlinear susceptibility, which can only be realized in non-Hermitian optical systems. Such an effect may be used for realizing all-optical table-top XUV lasers. We will also discuss our first demonstration of this novel effect in a wave system using coupled acoustic Fabry-Perot cavities.