Abstract Free-electron lasers (FELs) can emit light with different optical polarizations including linear, elliptic and circular corresponding to the characteristics of undulators used. X-ray FELs depend upon long undulator lines consisting a sequence short undulators. Linearly polarized are most commonly used; hence output is linearly polarized. Alternately, APPLE-II, Delta designs, or alterna...

Cavity modification of material properties and phenomena is a novel research field largely motivated by the advances in strong light-matter interactions. Despite this progress, exact solutions for extended systems strongly coupled to photon are not available, both theory experiments rely mainly on finite-system models. Therefore paradigmatic example an exactly solvable system cavity becomes hig...