Characteristics of a saturated 18.9-nm tabletop laser operating at 5-Hz repetition rate

We report the characteristics of a saturated high-repetition rate Ni-like Mo laser at 18.9 nm. This table-top soft X-ray laser was pumped at a 5-Hz repetition rate by 8-ps 1-J optical laser pulses impinging at grazing incidence into a precreated Mo plasma. The variation of the laser output intensity as a function of the grazing incidence angle of the main pump beam is reported. The maximum laser output intensity was observed for an angle of 20°, at which we measured a small signal gain of 65 cm^-1 and a gain-length product g×l>15. Spatial coherence measurements resulting from a Young´s double-slit interference experiment show the equivalent incoherent source diameter is about 11 μm. The peak spectral brightness is estimated to be of the order of 1×10²⁴ photons s^-1 mm^-2 mrad^-2 within 0.01% spectral bandwidth. This type of practical, small scale, high-repetition soft X-ray laser is of interest for many applications.