G. Shimkaveg

Short wavelength x-ray laser research at the Lawrence Livermore National Laboratory*

Laboratory x‐ray lasers are currently being studied by researchers worldwide. This paper reviews some of the recent work carried out at Lawrence Livermore National Laboratory. Laser action has been demonstrated at wavelengths as short as 35.6 A while saturation of the small signal gain has been observed with longer wavelength schemes. Some of the most successful schemes to date have been collisionally pumped x‐ray lasers that use the thermal electron distribution within a laser‐produced plasma to excite electrons from closed shells in neon‐ and nickel‐like ions to metastable levels in the next shell. Attempts to quantify and improve the longitudinal and transverse coherence of collisionally pumped x‐ray lasers are motivated by the desire to produce sources for specific applications. Toward this goal there is a large effort underway to enhance the power output of the Ni‐like Ta x‐ray laser at 44.83 A as a source for x‐ray imaging of live cells. Improving the efficiency of x‐ray lasers in order to produce s...

Observation of soft x‐ray amplification in neonlike molybdenum

Thin molybdenum coated foils have been irradiated in line focus geometry with from 3 to 8×1014 W cm−2 of 0.53‐μm light at the Nova laser. The resulting exploding foil plasma has demonstrated x‐ray laser gain at four wavelengths (106.4, 131.0, 132.7, and 139.4 A), identified as 3s‐3p transitions in neonlike Mo. The J=0–1, a 3s–3p transition at 141.6 A has been identified, but does not show evidence of significant gain in disagreement with the theory.

Ionization balance and gain calculations for neon-like selenium x-ray laser plasmas

Abstract We have developed compact collisional-radiative models to describe the ionization balance and excitation mechanisms in neon-like selenium x-ray laser plasmas. These models can be used for calculations of the ionization dynamics, detailed emission spectra, and gain coefficients. Careful attention has been paid to indirect processes such as dielectronic recombination, excitation-autoionization, and resonant excitation. We discuss the importance of different atomic processes and model approximations in the ionization balance and gain calculations. These results will be compared to experimental measurements and to previous calculations.

Ray and wave optics modeling of laboratory x-ray lasers

Much progress has been made recently in characterizing the emission from neon- like Yttrium exploding foil x-ray lasers. Concomitant with that effort, we have carried out detailed modeling to enhance our understanding of the experiments and improve their design. Our modeling includes target hydrodynamics, calculation of gain, and both ray and wave optics propagation. We will describe our modeling of Yt x-ray lasers, including first simulations using a two transverse dimensional gain calculation. Our calculations indicate that the time-integrated signal is very sensitive to the time history of the gain, because of the rapid sweep of the beam in angle measured with respect to the plane of the foil.

Lawrence Livermore National Laboratory X-Ray Laser Research: Recent Results

Since the successful demonstration of gain in neon-like selenium using an exploding foil amplifier, the x-ray laser group at Lawrence Livermore National Laboratory has investigated further the exploding foil amplifier concept for use in XUV lasers. Results are reported of the characteristics of selenium amplifiers up to 50 mm in length. Observation of at least 16 gain lengths for the 206 Å line of selenium is reported. Output powers in excess of 1 MW have been measured in pulses of approximately 200 picoseconds. The effects of refraction on the performance of long amplifiers have been studied. The occurrence time of the x-ray laser output relative to the input heating pulse has been measured and found to be in disagreement with a recent model that suggests three-body recombination driven by rapid radiative cooling as the inversion process in the selenium plasma.

Time resolved measurement of electron temperatures of exploding foil x-ray laser plasmas

Abstract We present results of recent experiments to measure the plasma conditions present in a neon-like x-ray laser plasma. We measure the time-resolved K -shell emission spectra of low Z tracer material doped into a yttrium exploding foil target. We determine the plasma conditions by analysing the K -shell emission spectra assuming a quasi-steady state approximation. Two dimensional LASNEX hydrodynamics simulations are in reasonable agreement with these time-resolved electron temperatures.

High resolution XUV spectroscopy of x-ray laser plasmas

This paper discusses recent progress in LLNLs high resolution XUV spectroscopy efforts with x-ray laser plasmas. We describe the instrumentation used, and we present preliminary time-resolved data on the spectral profiles of several XUV (extreme ultraviolet) lines from Ne- like Se and Ne-like Y x-ray lasers which have been obtained with instrumental resolutions ((lambda) /(Delta) (lambda) ) of approximately 10,000. The Se data indicates that the 206.4 angstroms J equals 2 - 1 laser line narrows below the expected 400 eV Doppler width (35 m angstroms) when amplified through approximately 6 gain lengths, while the Y data shows no evidence of the J equals 0 - 1 laser predicted to be nearly resonant with the J equals 2 - 1 laser at 154.9 angstroms.

Status of the Nova x‐ray laser experiments

We review the progress of the x‐ray laser experiments done at the Nova Laser facility. To data we have achieved lasing at wavelengths as short as 10.5 nm and output powers to ∼1–10 MW in a pulsewidth of 175 psec FWHM. We are experiencing considerable x‐ray laser beam breakup for exploding foil amplifiers ≳30 mm in length. We also describe our plans for achieving single‐mode fully‐saturated lasers at wavelengths <4.4 nm.

Highly charged ions in hot, dense plasmas

Highly‐charged ions play a critical role in hot, dense plasmas. They affect the energy balance and hydrodynamic evolution of transient plasmas. The radiation emitted by highly charged ions may be used in several practical applications, such as inertial confinement fusion, short wavelength lasers, and x‐ray sources for lithography and microscopy applications. This radiation may also be used to diagnose the conditions in plasmas, In recent years, models have been developed to describe the atomic kinetics of complex ionization states of highly charged ions in plasmas. However, reliable atomic calculations and careful experiments which test both the fundamental atomic physics and the assumptions of the plasma emission models are required.

YB66 as a new soft x‐ray monochromator for synchrotron radiation (abstract)

YB66, a complex binary semiconducting compound with a cubic crystal structure and a lattice parameter of 23.44 A, is potentially a very good candidate for monochromatization of soft x‐ray synchrotron radiation. The features such as: a large interatomic spacing, lack of absorption edges by the constituent elements in the region 1–2 keV, very narrow intrinsic rocking curves for (400) and (222) reflections and good thermal and mechanical properties make the material very useful. Using the known structure factors for the (400) and (222) reflections, having 2d values of 11.76 and 13.53 A, respectively, their rocking curves have been calculated and are shown [J. Wang, G. Shimkaveg, W. Goldstein, M. Eckart, T. Tanaka, Z. Rek, H. Tompkins, Nucl. Instrum. Methods A 291, 243 (1990)] to be comparable to or better than that of beryl (1010). A novel indirect heating floating zone method for growing large size crystals was used by Tanaka and his coworkers in Japan [T. Tanaka, S. Otani, and Y. Ishizawa, J. Cryst. Growt...