Petahertz-bandwidth spectral combs from the amplified spontaneous emission of a collisional plasma-based x-ray laser

Abstract

The possibility of generating spectral combs of petahertz bandwidth is demonstrated from amplified spontaneous emission (ASE) of a collisional plasma-based x-ray laser when its active medium is irradiated with a linearly polarized near-infrared (IR) laser field. It is shown that at a sufficiently high IR-field intensity these combs correspond to a sequence of subfemtosecond beats of extreme ultraviolet (XUV) radiation of a deterministic shape. At the same time, at a lower IR-field intensity ASE remains quasimonochromatic, but its frequency shifts as a result of the IR-field-induced quadratic Stark effect. In this case, the frequency tuning range of XUV radiation is approximately twice the frequency of the modulating IR field. In addition, modulation by the IR field leads to amplitude and frequency discrimination of the polarization components of ASE, parallel and orthogonal to the IR field. The possibility of observing these effects is analyzed for a collisional plasma x-ray laser based on neon-like Ti12+ ions with an unperturbed ASE wavelength of 32.6 nm and a modulating field with a wavelength of 1 {\mu}m and an intensity in the range of 10^16 - 10^17 W/cm^2.