We present polarization measurement of a Ni-like Ag x-ray laser working in the transient collisional excitation scheme. A calibrated membrane multilayer beam splitter was used to determine the energies of two mutually perpendicular polarization components ($s$ and $p$ components). As a result, we observed a high degree of polarization that fluctuated from shot to shot. The dominant polarization component switched from $s$ to $p$ when pumping was made stronger. The measurement results are discussed from the point of view of the general polarization theory and supported by a numerical simulation based on Maxwell-Bloch equations. The physical processes causing the dominance of one polarization component are discussed in terms of pumping strength. These results should extend the wave physics perspective on the amplification process, transforming a weak random noise into a strong coherent radiation.

• Received 8 April 2015

DOI:https://doi.org/10.1103/PhysRevA.92.043807