Near‐infrared‐to‐vacuum‐ultraviolet high‐harmonic Raman and plasma emission spectroscopy with ultrashort mid‐infrared laser pulses

We demonstrate a new modality of ultrafast laser spectroscopy based on high‐harmonic‐driven stimulated Raman scattering (hi‐SRS) and incoherent laser‐plasma emission (iLPE). The spectra of high‐order harmonics driven by sub‐100‐fs pulses in the mid‐infrared are shown to display well‐resolved Raman‐gain, Raman‐loss, and iLPE features, enabling a chemically specific, single‐beam, single‐shot spectroscopy of gases and plasmas within a spectral range stretching from the near‐infrared to vacuum ultraviolet. We present a theoretical framework based on a suitably adapted nonlinear evolution equation that enables a closed‐form description of hi‐SRS as an ultrafast nonlinear‐optical phenomenon. We show that the content of hi‐SRS as a physical process and as a method of spectroscopy goes well beyond standard SRS, offering a powerful resource for spectroscopy, remote sensing, and ultrafast optical science. Standing out as particularly relevant for nitrogen‐containing gas systems, including atmospheric air, is a multimodal spectroscopic probe that combines ultrafast hi‐SRS via the second positive system of molecular nitrogen with iLPE via the γ band of nitrogen monoxide. We demonstrate a new modality of ultrafast laser spectroscopy based on high‐harmonic‐driven stimulated Raman scattering and incoherent laser‐plasma emission.