Demonstration of x-ray amplification in transient gain nickel-like palladium scheme

We report experimental results of x-ray amplification of spontaneous emission in a Ni-like transient collisional excitation scheme. The Ni-like plasma formation, ionization, and collisional excitation requires irradiation of a slab target by two laser pulses: a formation beam with 5 J energy of 800 ps duration and a pump beam of 5 J energy in 1.1 ps. A gain of 35 cm(-1) and a gL product of 12.5 are measured on the 4d --> 4p J = 0 --> 1 transition for Ni-like Pd at 147 Angstrom with an 8 mm line focus. The high efficiency of this scheme at "table-top" laser energies is a direct consequence of the nonstationary population inversion produced by the high intensity picosecond pulse.