Diffractive optics based two-color six-wave mixing: phase contrast heterodyne detection of the fifth order Raman response of liquids

Fifth order Raman scattering is extremely sensitive to anharmonicities and nonlinear polarizabilities and thus provides a unique probe of the many-body potential of liquids. The weak signals from this high order, χ(5), process are complicated by cascaded lower-order χ(3) processes. A new approach has reduced the beam delivery to a single diffractive optic that generates the beam pattern for phase-matched six-wave mixing, and passively phase locks all six fields. Heterodyne detection introduces signal amplification and phase contrast against lower-order nonlinearities. The findings provide new insight into the nature of the direct χ(5) nonlinear response function and two-time correlation of liquids.