Robert H. Price

X‐ray Microscopy Using Grazing Incidence Reflection Optics

The Kirkpatrick-Baez microscopes are described along with their role as the workhorse of the x-ray imaging devices. This role is being extended with the development of a 22X magnification Kirkpatrick-Baez x-ray microscope with multilayer x-ray mirrors. These mirrors can operate at large angles, high x-ray energies, and have a narrow, well defined x-ray energy bandpass. This will make them useful for numerous experiments. However, where a large solid angle is needed, the Woelter microscope will still be necessary and the technology needed to build them will be useful for many other types of x-ray optics.

Gold transmission gratings with submicrometer periods and thicknesses ≳0.5 μm

Gold gratings with spatial periods of 0.3 and 0.2 μm have been fabricated in thicknesses of 0.6 and 0.25 μm, respectively, and used in x‐ray spectroscopy and spatial‐period‐division. Fabrication techniques included: holographic lithography, shadowing, x‐ray lithography, and gold microplating. Control of linewidth to tolerance of the order of 10 nm has been demonstrated for gratings of 0.2 μm period. A high resolution imaging spectrometer, composed of a 22× Wolter x‐ray microscope in conjunction with a gold transmission grating, was tested. At a wavelength of 0.69 nm, a resolving power, λ/Δλ, of 200 was demonstrated. Resolution in this case was source‐size limited. Gratings of 99.5 nm period were exposed in PMMA by x‐ray (λ = 4.5 nm) spatial‐period‐division.

Imaging x-ray spectrometer for laser fusion applications.

A gold transmission grating has been coupled to a high-resolution Wolter-design grazing-incidence reflection x-ray microscope to produce an imaging x-ray spectrometer of unprecedented spatial resolution, spectral range, and collection solid angle. In a series of test experiments conducted at 1.75-2 keV, the instrument demonstrated a spectral resolving power, lambda/Deltalambda, of 200 and a 1-D spatial resolution of 1 microm. The spectrometers large collection solid angle, approximately 2 x 10(-5) sr, and broad spectral range, from the near UV to 3.2 keV, make it a very versatile instrument for laser-fusion applications.

Ultrafast Gated Intensifier Design for Laser Fusion X-Ray Framing Applications

The transmission line imager described above is now in fabrication and some of the important characteristics of its components have been tested. The design of the device addresses all of the stringent requirements for ICF framing applications and proposes solutions to many of the problems limiting the performance of other designs in use and described in the literature. The two most important features of this device are its very short gating time and its high image quality. The high speed results from the integral photoconductive-switch pulse generator, matched vacuum transmission line geometry, and small high-conductivity photocathode. The small photocathode is made possible because of the high resolution of the proximity focused imager and the special high contrast phosphor screen. The phosphor screen incorporates the unique feature of an electron collimator which serves both to: 1) increase the shutter ratio by attenuating x-rays which reach the screen, and 2) prevent Rutherford scattered electrons from re-impacting the screen in another location, impairing the image contrast ratio and edge response. The resolution and edge response of the screen is also enhanced by the narrow transverse electron energy distribution of the photocathode and the isolation between the islands of phosphor at the end of each fiber of the screen. If this design is successful in all respects it will make possible short frame time quantiative images of ICF phenomenon of unprecedented quality.

Space And Time Resolved Soft X-Ray Spectra Using X-Ray Transmission Gratings

Gold transmission gratings with 0.3 Am spatial period, 0.6 Am thick have been fabricated and are being used for the spectroscopy of high temperature, laser-produced plasmas. A transmission grating has been coupled with a soft x-ray streak camera, producing the first time resolved (20 psec resolution) continuous x-ray spectrum over the range 0.1 to 1.5 keV from a laser-produced plasma. In addition, a transmission grating has been coupled with a high resolution, Wolter-design x-ray microscope to produce an imaging spectrometer of unprecedented spatial and spectral resolution. In laboratory experiments the imaging spectrometer demonstrated a spectral resolving power, (A/AA) of 200 and a spatial resolution of 1 µm.

Laser plasma coupling in long pulse, long scale length plasmas

Laser plasma coupling under near reactor‐size target conditions is studied at Iλ2≂1014 W/cm2 μm2 with 1‐mm size plasmas, 3‐kJ, 3‐ns irradiations on the 1.064‐μm Shiva laser. Evidence for the occurrence of parametric processes, such as stimulated Brillouin sidescatter and the two‐plasmon decay instability, is observed.

Soft X‐ray spectroscopy Using Thick Gold Transmission Gratings of 0.2 to 0.3 μm Spatial Periods

We have fabricated and tested transmissin diffraction gratings with spatial periods of 0.2 and 0.3 μm and gold thicknesses of 0.25 and 0.65 μm respectively. The fabrication process included holographic lithography, ion milling, x‐ray lithography and gold and gold microplating. The gratings were coupled to a Wolter‐type 22x grazing incidence microscope, forming a high resolution imaging spectrometer. This spectrometer demonstrated a spatial resolution of ∼1 μm and a resolving power, λ/Δλ, ≳200 at .69 nm. The observed spectral resolution, Δλ, was source size limited.

Streaked X-Ray Microscopy Of Laser Fusion Targets

An ultrafast soft x-ray streak camera has been coupled to a Wolter axisymmetric x-ray microscope. This system was used to observe the dynamics of laser fusion targets both in self emission and backlit by laser produced x-ray sources. Spatial resolution was 7 pm and temporal resolution was 20 ps. Data is presented showing the ablative acceleration of foils to velocities near 107 cm/sec and the collision of an accelerated foil with a second foil, observed using 3 keV streaked x-ray backlighting. Good agreement was found between hydrocode simulations, simple models of the ablative acceleration and the observed velocities of the carbon foils.

Time and space resolved measurements of the dynamics of laser fusion targets

A time resolved radiography system has been recently implemented at the Shiva Laser Facility. The radiography system allows measurement of motions in one spatial dimension and one time dimension with a resolution of 4.5 μm and 15 ps respectively, at x‐ray energies selected in the range of 0.1 keV to 2 keV. The dynamic range of the system is 103. Modifications will extend the capability of the system to a dynamic rnge of 104 for x‐ray energies up to 8 keV. The streaked axisymmetric x‐ray microscope optical alignment system allows pointing to 5 μm accuracy. Results of recent experiments are described, including the dynamis of the blowoff of laser irradiated disk targets. Measurement of velocities near 107 cm/sec for laser irradiated disk targets has been accomplished by use of x‐ray backlighting.