COLLISIONAL EXCITATION X-RAY LASERS - TOWARD A COMPACT X-RAY SOURCE

Soft x-ray amplification has been observed over the wavelengths of 14. 3 nm - 4.6 nm in nickel-like ions of various atoms with the atomic num bers of Z = 47 (Ag) to 72 (Hf). These results were obtained by irradia tion of a preformed plasma with a short duration laser pulse, Observat ion of polarization of the amplified soft x-ray radiation infers that the population inversion is strongly affected by the trapping of the r esonance radiation. Conditions for increasing the population inversion density by pumping with shorter-duration laser pulses due to transien t effects are examined.