Yttrium X-ray Laser Research Articles

Extreme ultraviolet probing of laser imprint in a thin foil using an x-ray laser backlighter

For direct drive inertial confinement fusion, a capsule is imploded by directly illuminating the surface with laser light. Beam smoothing and uniformity of illumination affect the seeding of instabilities at the ablation front. We have developed a technique for studying the imprint of a laser beam on a thin foil using an x-ray laser as an extreme ultraviolet (XUV) backlighter. We use multilayer XUV optics to relay the x-ray laser onto the directly driven foil, and then to image the foil modulation onto a charged coupled device camera. This technique allows us to measure small fractional variations in the foil thickness. We have measured the modulation due to imprint from a low intensity 0.35 μm drive beam incident on a 3 μm Si foil using an yttrium x-ray laser on Nova. We present results from a similar technique to measure the imprinted modulation due to a low intensity 0.53 μm drive beam incident on a 2 μm Al foil using a germanium x-ray laser at the Vulcan facility.

Measurement of 0.35 microm laser imprint in a thin Si foil using an x-ray laser backlighter.

Imprinted modulations in optical depth of a thin Si foil due to 0.35 \ensuremath{\mu}m laser irradiation at about $3\ifmmode\times\else\texttimes\fi{}{10}^{12}$ W/c${\mathrm{m}}^{2}$ have been measured at shock breakout. These measurements were made by high resolution face-on radiography using a gain saturated yttrium x-ray laser backlighter operating at a wavelength of 15.5 nm with a multilayer optics imaging system. The imprinted modulation due to a static speckle pattern and a 0.29 and a 0.33 THz spectral dispersion smoothed speckle pattern were studied. Comparison of the imprinted modulation is made with simulations.

X-ray laser radiography of perturbations due to imprint of laser speckle in 0.35 μm laser irradiation of a thin Si foil

A gain saturated yttrium x-ray laser operating at a wavelength of 15.5 nm has been used as an extreme ultraviolet probe to measure optical depth modulations in a thin Si foil by face-on radiography. The high brightness of this Ne-like x-ray laser allows probing of a sample with a high opacity. This technique is sensitive to very small modulations in the optical depth of the foil, corresponding to thickness variations of a few 10 nm of cold material. This technique is used to measure the effect of direct drive laser imprint on a thin Si foil by face-on radiography using multilayer optics to image the foil with 26× magnification. We have recorded modulations in a thin Si foil that was irradiated by a 400 ps, 0.35 μm beam at an intensity of about 3×1012 W/cm2.

Dynamics of a multiple-pulse-driven x-ray laser plasma

In this paper we describe experimental and computational studies of multiple-pulse-driven laser plasma, which is the gain medium for a neon-like yttrium x-ray laser. Near-field emission profiles have been measured both with and without reinjection of the x-ray laser photons to couple with the amplifying medium created by later pulses using an external multilayer mirror. From the temporal and spatial evolution of the near-field emission profiles we can examine the pulse-to-pulse variation of the x-ray laser plasma due to changes in the hydrodynamics, laser deposition, and the injecting of x-ray laser photons back into an amplifying x-ray laser plasma. Using a combination of radiation hydrodynamics, atomic kinetics, and ray propagation codes, reasonable agreement has been obtained between simulations and the experimental results.

Application of x-ray-laser interferometry to study high-density laser-produced plasmas

Collisionally pumped soft-x-ray lasers now operate over a wavelength range extending from 4 to 40 nm. With the recent advances in the development of multilayer mirrors and beam splitters in the soft-x-ray regime, we can utilize the unique properties of x-ray lasers to study large, rapidly evolving laser-driven plasmas with high electron densities. Using a neonlike yttrium x-ray laser, which operates at a wavelength of 15.5 nm, we have performed a series of radiography, moiré deflectometry, and interferometry experiments to characterize plasmas relevant to inertial confinement fusion. We describe experiments using a soft-x-ray laser interferometer, operated in the Mach–Zehnder configuration, to study CH plasmas. The two-dimensional density profiles obtained from the interferograms allow us to validate and benchmark our numerical models used to study the physics of laser–plasma interactions.

Two-dimensional interferogram of an exploding selenium foil using a soft X-ray laser interferometer

We have developed a soft X-ray interferometer capable of probing large high-density plasmas with micron spatial resolutions. A neon-like yttrium X-ray laser operating at 155 /spl Aring/ was combined with the Mach-Zehnder interferometer to obtain electron density profiles of a laser-produced exploding selenium foil plasma. The plasma was produced with one Nova laser beam using a 120-/spl mu/m line focus, the same conditions used to create a selenium X-ray laser. The interferogram of the selenium plasma was obtained from an end-on perspective.

Fringe formation and coherence of a soft-x-ray laser beam illuminating a Mach–Zehnder interferometer

We investigated the fringe visibility produced by a Mach-Zehnder interferometer illuminated by a collisionally pumped yttrium x-ray laser operating at 15.5 nm. Fringe visibility varied as a function both of relative path delay and of relative spatial overlap of the beams. This visibility information was extracted quantitatively from several interferograms and analyzed to produce a characterization of the temporal coherence, yielding a gain-narrowed linewidth of 1.3 pm for the 15.5-nm laser transition and spatial coherence consistent with an effective source size of approximately 220 microm +/- 50% at the x-ray laser output.

Electron Density Measurements of High Density Plasmas Using Soft X-Ray Laser Interferometry.

We have developed and used for the first time a soft x-ray interferometer to probe a large laser-produced plasma with micron spatial resolutions. A neonlike yttrium x-ray laser operating at 155 \AA{} was combined with a multilayer coated Mach-Zehnder interferometer to obtain electron density profiles in a plasma produced by laser irradiation of a CH target. The measured electron density profile has been compared to hydrodynamic simulations and shows good agreement near the ablation surface but some discrepancy exists at lower densities.

X-ray lasers as sources for resonance-fluorescence experiments

We point out that existing Ne-like X-ray lasers have sufficient brightness to be used as pump sources in resonant pump-fluorescence experiments, and we discuss some of the potential benefits and limitations of such experiments. In preliminary experiments, we have measured the line overlap of the Ne-like yttrium X-ray laser near 155 A with 4f−3d transitions in H-like Na and He-like Mg. These experiments used a high-resolution grating spectrometer, and calibrated the wavelength of the yttrium laser by comparison against lines of known wavelength. The results indicate that the wavelength of the yttrium laser is 154.985 ± 0.025 A, a factor of 2–4 improvement in precision over previous calibrations. We find that the yttrium laser is ≈ 100 mA to the long-wavelength side of both the He-like Mg line and the H-like Na line, so that neither resonance is perfect; however, Stark broadening could improve the overlap in the latter scheme, and bulk Doppler shifting could improve both resonances. We also find a good resonance between the yttrium laser and an un-identified transition which we tentatively attribute to copper.

Power measurements of a saturated yttrium x-ray laser

We report on measurements of the output power from the J = 2–1 (λ = 15.5 nm) neonlike yttrium soft-x-ray laser. The results show peak powers of 32 MW in an output pulse width of 200 ps (FWHM) and an integrated energy of 7 mJ. The output is consistent with the expected saturation intensity of this laser and makes this system one of the brightest XUV sources available.

An argon-pumped yttrium X-ray laser

We propose using the He-α emission line of argon to resonantly photopump neon-like yttrium and produce lasing on several 3p → 3s transitions ranging from 79 to 217 Å. Calculations of the gain of these laser transitions in steady-state equilibrium plasmas are presented. Experimentally, the resonance between the He-α argon line and the neon-like yttrium 2p → 5d is confirmed on the electron beam ion trap.

Predicted four-wave mixing and tripling rates for neonlike yttrium x-ray laser radiation in sodiumlike plasmas

Presented are predicted conversion rates for four-wave mixing of the output of the Ne-like Y soft-x-ray laser (15.495 nm) with that of an optical laser in a Na-like Ca plasma to give radiation at ~ 7.8 nm (approximate frequency doubling). Also presented are frequency tripling rates of the Ne-like Y laser in a Na-like V plasma to give radiation at 5.165 nm. In each case the nonlinear susceptibilities and converted intensities are calculated, and phase-matching considerations are discussed.