Pulse buildup from noise and intrinsic polarization of plasma-based x-ray lasers

The paper presents a theoretical analysis of the pulse buildup from the spontaneous noise level and variations in the intrinsic polarization state of x-ray lasers, devices utilizing amplified spontaneous emission in a high-gain medium. Maxwell-Bloch equations with incorporated randomness of spontaneous emission, atomic level degeneracy, and time-dependent gain are used to describe the wave nature of the amplification process properly. The dynamics of pulse growth and polarization variation are analyzed for the entire amplification process starting from the initial state of random noise to the full saturation. It is shown that, within the used one-dimensional model, the output pulse can be polarized to a substantial degree. These results provide the basic understanding of x-ray lasers in a wave-optics perspective.