The temporal profile of the amplification gain of the neonlike manganese x-ray laser in the transient collisional excitation scheme was measured by the use of the 29th-order harmonic light at a wavelength of $26.9\mathrm{nm}$ as a probe beam. The raise-up time of the gain was delayed by $20\mathrm{ps}$ from the peak of the pumping laser pulse, and the duration of the gain was $50\mathrm{ps}$. This method is a promising powerful tool to realize the highly coherent x-ray laser beam by using a combination of an x-ray seeder and an x-ray amplifier.

• Received 15 December 2006

DOI:https://doi.org/10.1103/PhysRevA.76.043805