Visible spectroscopy of the underwater Ag-wire explosion

Summary form only given. Discharge-pumped soft X-ray laser devices were designed and manufactured in many laboratories in the world. All of them, which are routinely functioning, achieve population inversion according to electron-collisional excitation pumping scheme. However, scaling down their wavelength has been unsuccessful not only because it requires much larger power, but also because it needs homogeneously pre-filled capillary with vapours of metallic elements like Pd (laser wavelength 14.7 nm), Ag (14.0 nm), Cd (13.2 nm), In (12.6 nm), Sn (12.0 nm). Vapour injection into the capillary has not yet been successful and exploding wire in free space is not stable. Therefore, other possible solutions are to explode wire in a capillary, to ablate metallic ring structure in a capillary, or to ablate a capillary wall containing metallic elements. However, in all these cases, similarly as at vapour injection, a conducting layer on the capillary walls is formed that from time to time has to be removed. Another solution is the wire explosion in a liquid: in this case the proximity of liquid wall can stabilize plasma column similarly as proximity of solid wall stabilizes a Z- pinch in a capillary. The problem of efficient energy deposition into the plasma channel made us to study in detail the processes during wire explosion - namely the creation and development of water- vapour-layer at the wire surface. For that, in parallel to electrical measurements (discharge current and voltage) also the time development of visible emission (both spectrally integrated {by PIN diode}, and spectrally resolved {by spectrograph} was registered and evaluated.