Demonstration of transient gain x-ray lasers near 20nm for nickellike yttrium, zirconium, niobium, and molybdenum

We demonstrate strong lasing on the Ni-like 4d(1)S(0)?4p(1)P(1) transition at 18.9, 20.3, 22.0, and 24.0 nm for Mo, Nb, Zr, and Y ions, respectively, using the transient collisional excitation scheme. Approximately 5 J of laser energy in a combination of a 600-ps pulse and a 1-ps pulse from the Compact Multipulse Terawatt (COMET) tabletop laser system is used to irradiate slab targets of these materials. Small-signal gains of 17-26cm (-1) are determined on the 4d?4p transition, with overall gain-length products gL of 11-12. Lasing is observed and gain is measured on the 4f(1)P(1)?4d(1)P(1) transition, which is pumped by collisional excitation combined with self-photopumping, for what is to our knowledge the first time.     

Observation of a multiply ionized plasma with index of refraction greater than one

We present clear experimental evidence showing that the contribution of bound electrons can dominate the index of refraction of laser-created plasmas at soft x-ray wavelengths. We report anomalous fringe shifts in soft x-ray laser interferograms of Al laser-created plasmas. The comparison of measured and simulated interferograms shows that this results from the dominant contribution of low charge ions to the index of refraction. This usually neglected bound electron contribution can affect the propagation of soft x-ray radiation in plasmas and the interferometric diagnostics of plasmas for many elements.     

Saturated high-repetition-rate 18.9-nm tabletop laser in nickellike molybdenum

We report saturated operation of an 18.9-nm laser at 5-Hz repetition rate. An amplification with a gain-length product GL of 15.5 is obtained in the 4d 1S0-4p 1P1 laser line of Ni-like Mo in plasmas heated at grazing incidence with approximately 1-J pulses of 8.1-ps duration from a tabletop laser system. Lasing is obtained over a broad range of time delays and pumping conditions. We also measure a GL of 13.5 in the 22.6-nm transition of the same ion. The results are of interest for numerous applications requiring high-repetition-rate lasers at wavelengths below 20 nm.     

Diagnostics of the temperature of a plasma created by a CO2 laser,from the UV radiation spectrum

Delivered at the Fifth All-Union Conference on Diagnostics of a High-Temperature Plasma (18–22 June, 1990, Minsk).     

Bow shocks formed by plasma collisions in laser irradiated semi-cylindrical cavities

The formation of shocks in plasmas created by short pulse laser irradiation (λ = 800 nm, I ≈ 1 × 10¹² W cm^?2) of semi-cylindrical cavities of different materials was studied combining visible and soft X-ray laser interferometry with simulations. The plasma rapidly converges near the axis to form a dense bright plasma focus. Later in time a long lasting bow shock is observed to develop outside the cavity, that is shown to arise from the collision of plasmas originating from within the cavity and the surrounding flat walls of the target. The shock is sustained for tens of nanoseconds by the continuous arrival of plasma ablated from the target walls. The plasmas created from the heavier target materials evolve more slowly, resulting in increased shock lifetimes.     

Shadowgrams of a dense micro-capillary plasma obtained with atable-top soft X-ray laser

A sequence of high resolution shadowgrams that map the evolution of the plasma of a 380 μm diameter microcapillary discharge was obtained using a very compact 46.9 nm laser. These images are the first plasma diagnostics data obtained using a table-top soft X-ray laser     

Picosecond x-ray laser interferometry of dense plasmas

We present the first results from picosecond interferometry of dense laser-produced plasmas using a soft x-ray laser. The picosecond duration and short wavelength of the 14.7 nm Ni-like Pd laser mitigates effects associated with motion blurring and refraction through millimeter-scale plasmas. This enables direct measurement of the electron-density profile to within 10 microm of the target surface. A series of high-quality two-dimensional (2D) density measurements provide unambiguous characterization of the time evolution in a fast-evolving plasma suitable for validation of existing 1D and 2D hydrodynamic codes.