LAUSR

Twisted light beams with orbital angular momentum provide an additional degree of freedom in controlling light-matter interactions, which are interesting for fundamental and applied research. Although there are various methods that can produce twisted laser beams at sub-micrometer or shorter wavelengths, it is still challenging to extend such beams to mid-infrared (mid-IR) wavelengths with relativistic intensity. Here, we present a promising scheme to generate such pulses converted through frequency downshift of intense driver optical pulses via a plasma-based photon decelerator. The resulting near-single-cycle vortex pulses cover a broad mid-IR spectral range up to 18 μm with energy conversion efficiency of 4.8% (energy ~150mJ) in the wavelength range above 7 μm. This long-wavelength infrared pulses at the terawatt level can be focused to relativistically high intensity, which may offer significant opportunities for high-field physics and ultrafast applications.