We are prosing to seed an inversely-populated plasma as a lasing medium using coherent VUV, XUV and SXR radiation: For the attosecond VUV seed pulses, we would use plasmas with the highly-populated Rydberg states in the VUV spectral region (i.e. Xe, Ar, and Ne gas plasmas).

For the SXR seed, we would use stimulated emission from a plasma medium with highly-charged ions such C5+, as described in the proposal.

Here, we are showing a detailed concept of seeding a He plasma medium, generated in a plasma capillary discharge, with inversion-population in the He* Rydberg series (i.e. the 2p state is in the XUV spectral domain with energy of 21 eV). An XUV beam would stimulate emission from He*. A monochromatic fs XUV seed pulse would be generated by a 390 nm intense femtosecond beam in Kr gas. Al and Sn filters would filter-out harmonics below and above the 7th one (see the upper-right inset for 390 nm driving laser). This would be a demonstration of a first lasing plasma medium seeded by coherent XUV radiation.