Strong quantum interferences in frequency up-conversion towards short vacuum-ultraviolet radiation pulses

Abstract

We present experimental data on quantum interferences in resonantly enhanced frequency up-conversion towards the vacuum-ultraviolet spectral regime. The process is driven in xenon atoms by ultrashort (picosecond) laser pulses. We use two simultaneous frequency conversion pathways via an excited intermediate state, i.e., fifth harmonicgenerationofthefundamentalwavelengthandfour-wavemixingofthefundamentalandtwophotonsof itssecondharmonicwavelength.Bothconversionpathwaysyieldradiationat102nm.Thetwopathwaysinterfere, depending on the relative phase of the fundamental and second harmonic. By appropriate choice of the phase we get constructive interference (resulting in increased conversion efficiency) or destructive interference (resulting in reduced conversion efficiency). The total conversion yield shows very pronounced constructive and destructive quantum interference with a visibility of roughly 90%. A stable and highly accurate phase control setup enables suchstrongquantuminterferencesformorethan260oscillationcycles.Inanextensionoftheexperiment,simultaneouslytofrequencyconversionwealsomonitorlaser-inducedfluorescenceasameasurefortheexcitationprobabilitytotheexcitedintermediatestate.Also,intheexcitationprobabilityweobservestrongquantuminterferences. As an interesting feature, a small phase lag occurs between the quantum interference patterns of frequency conversion and population transfer. This is due to an additional atomic phase acquired during frequency conversion.