We report the first demonstration of a high average power tabletop soft x-ray laser. An average laser output power of ഠ1 mW ͑.2 3 10 14 photons͞s͒ was generated at 46.9 nm in Ne-like Ar using a very compact tabletop discharge. The spatially coherent average power emitted by this 26.5 eV laser is comparable to that generated at this photon energy in a similar bandwidth ͑Dl͞l 10 24 ͒ by a thirdgeneration synchrotron beam line. Lasing was obtained at a repetition rate of 7 Hz with an average output energy of 135 mJ͞pulse by exciting a plasma column in a ceramic capillary with a fast current pulse. This very compact high-repetition-rate laser source makes intense short-wavelength coherent radiation accessible to a wide variety of new applications. [S0031-9007(98)08022-3]

As a first step in the design of a repetitive pulsed neutron generator, a very small plasma-focus device has been designed and constructed. The system operates at low energy (160 nF capacitor bank, 65 nH, 20–40 kV, and ∼32–128 J). The design of the electrode was assisted by a computer model of Mather plasma focus. A single-frame image converter camera (5 ns exposure) was used to obtain plasma images in the visible range. The umbrellalike current sheath running over the end of the coaxial electrodes and the pinch after the radial collapse can be clearly observed in the photographs. The observations are similar to the results obtained with devices operating at energies several orders of magnitude higher. The calculations indicate that yields of 104–105 neutrons per shot are expected with discharges in deuterium.

The basic engineering criteria for conceptual design of plasma focus devices is derived from a thermonuclear model, and applied successfully to the operation of small neutron pulsors. The theory is able to explain the variation of the neutron yield with the gas pressure in deuterium-filled chambers, the current evolution, and the electrode geometrical parameters. The performance of a prototype designed to optimize the flux/fluence ratio is presented, contrasting the experimental outcomes with the model. A set of effective design parameters is deduced, which ensure a band confidence of 20%.

We report what is believed to be the f irst demonstration of soft-x-ray interferometry of a plasma with a tabletop soft-x-ray laser. A Lloyd's mirror interferometer was used in combination with a very compact l 46.9 nm capillary-discharge-pumped laser to map the electron density in the cathode region of a pinch plasma. © 1999 Optical Society of America OCIS codes: 140.7240, 170.7440, 120.3180. Interferometry using optical lasers is a powerful technique for the diagnostics of plasmas that provides time-resolved two-dimensional maps of the electron density. However, free -free absorption and refraction of the probe beam limit the maximum electron density, plasma size, and plasma density gradients that can be probed with optical wavelengths. The development of soft-x-ray lasers has opened the possibility of extending plasma interferometry to shorter wavelengths, significantly expanding the range of plasma parameters that can be probed. Recently, a 15.5-nm Ne-like Y laser pumped by the Nova laser at Lawrence Livermore National Laboratories was used in combination with a skewed Mach -Zehnder interferometer to probe very high-density laser-created plasmas.1,2The amplitude-division interferometer used in those pioneering experiments was implemented by use of thin multilayer beam splitters and multilayer-coated mirrors developed for that wavelength. The advent of gain-saturated discharge-pumped tabletop soft-x-ray lasers 3,4 and the development of several saturated 5 or nearly saturated 6,7 soft-x-ray lasers pumped by relatively compact optical lasers will allow the probing of a great variety of dense plasmas. However, multilayer beam splitters cannot be developed for the wavelengths corresponding to some of these lasers at present, owing to the lack of materials with adequate optical constants. Alternatively, amplitude-division interferometers based on diffraction gratings 8 and wavefront-division interferometers 9,10 have been discussed. Recently, a Fresnel bimirror wave-front-division softx-ray interferometer was demonstrated 10 and was used in combination with a 21.2-nm Ne-like Zn laser to probe surface defects induced by an intense electric field. 11In this Letter we report what we believe to be the first use of a tabletop soft-x-ray laser in plasma interferometry. We have utilized a very compact l 46.9 nm capillary-discharge-pumped tabletop soft-xray laser in combination with a Lloyd's mirror 12 to probe the cathode region of a pinch plasma with subnanosecond time resolution. The maximum plasma electron density n e and size L that can be probed with this laser are significantly larger than those accessible with the fourth harmonic of a Nd : YAG laser at l 265 nm (free -free absorption,~n e 2 L, is significantly smaller at 46.9 nm, e.g., ഠ36 times smaller for a plasma with an electron temperature T e 100 eV). Moreover, larger plasma gradients can be probed at this short wavelength owing to the reduction of ഠ30 times in the refraction angle. A Lloyd's mirror is the simplest possible wave-front-division interfero...

We report on the operating parameters and laser output pulse characteristics of an extremely compact discharge-pumped 46.9-nm laser of a size comparable with that of many widely utilized visible and ultraviolet gas lasers. This capillary-discharge laser generated subnanosecond laser pulses with energies of as much as 25 mJ by single-pass amplification in an 18.6-cm-long argon-plasma column. Measurements of the laser output energy, pulse width, far-field beam profile, and beam divergence are reported.