Fig. 1. Soft X-ray amplification with nickel-like Ag ions.

Fig. 2. Layout of a soft X-ray laser composed of an oscillator and an amplifier.

Fig. 3. X-ray laser interferometer using a double Lloyd’s mirror for observation of ablation by fs laser irradiation. Inset, interference pattern with the fringe shift in the ablated region.

Fig. 4. (a) X-ray laser interference patterns of W at 48 and 71 ps after fs laser irradiation; (b) temporal evolution of the height of the ablation front, determined from the interference patterns.

Fig. 5. X-ray reflective images of the ablation region of W ranging from 19 to 258 ps after fs laser irradiation.