Enhanced XUV pulse generation at 89 nm via nonlinear interaction of UV femtosecond filaments

We demonstrated efficient generation of ultrafast extreme ultraviolet (XUV) pulses at 89 nm from an intense 267 nm UV femtosecond filamentation in argon gas. The XUV pulse generation efficiency was significantly enhanced through UV filament termination from the argon gas into the background vacuum that prevented backconversion of the generated third-harmonic XUV to the fundamental-wave UV pulses. This was further combined with noncollinear UV filament interaction that produced volume-plasma to pre-extract XUV pulses from the filament core, resulting in further XUV enhancement. The generated 89 nm XUV pulses reached what is so far, to our knowledge, the highest pulse energy of 190 nJ.