Laser-produced plasma water-window x-ray source by continuous liquid bismuth jet

We have demonstrated a continuous-operated water-window (WW) x-ray source using a regenerative liquid bismuth (Bi) jet for 120 min. A regenerative liquid Bi jet with a diameter of 35-40 µm was continuously injected into a vacuum. The number of photons per pulse was observed to be 3 × 10¹¹ photons/sr and 4.2 × 10¹¹ photons/sr at peak wavelengths of 4.1 nm and 4.3 nm, respectively, which arises from n = 4-n = 4 (Δn = 0) transitions, and 1.7 × 10¹¹ photons/sr at a peak wavelength of 2.8 nm, which is attributed to n = 4-n = 5 (Δn = 1) transitions. The total number of photons emitted/pulse in the 2.3-4.4 nm range was 10¹²-10¹³ photons/(nm · sr) for 120 min. We also observed that the fast on spectra scales with the laser intensity according to the power of 0.4 of the laser intensity. These results suggest that the continuous regenerative liquid Bi jet operation could credibly provide future shorter wavelength extreme ultraviolet (EUV) lithography and x-ray microscopy source for biological imaging applications.