This work details the method of obtaining time-integrated images of laser–plasma x-ray emission using charge-injection devices (CIDs), as has been demonstrated on the University of Rochester’s 60-beam UV OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. The CID has an architecture similar to a charge-coupled device. The differences make them more resistant to radiation damage and, therefore, more appropriate for some application in laser–plasma x-ray imaging. CID-recorded images have been obtained with x-ray pinhole cameras, x-ray microscopes, x-ray spectrometers, and monochromatic x-ray imaging systems. Simultaneous images obtained on these systems with calibrated x-ray film have enabled determination of the absolute detection efficiency of the CIDs in the energy range from 2 to 8 keV

Carbone, J.

Marshall, Frederic J.

McInnis, D.

Ninkov, Zoran

Ohki, Thomas

English

Name not available

Rochester Institute of TechnologyRIT Scholar WorksArticles2001Imaging of laser-plasma x-ray emission with charge-injection devicesFrederic MarshallThomas OhkiD. McInnisFollow this and additional works at: http://scholarworks.rit.edu/articleThis Article is brought to you for free and open access by RIT Scholar Works. It has been accepted for inclusion in Articles by an authorizedadministrator of RIT Scholar Works. For more information, please contact ritscholarworks@rit.edu.Recommended CitationReview of Scientific Instruments 72N1 Part 2 (2001) 713-716Imaging of laser–plasma x-ray emission with charge-injection devicesF. J. Marshalla) and T. OhkiLaboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester,New York 14623-1299D. McInnis and Z. NinkovRochester Institute of Technology, Rochester, New York 14623J. CarboneCID Technologies Inc., 101 Commerce Boulevard, Liverpool, New York 13088~Presented on 20 June 2000!This work details the method of obtaining time-integrated images of laser–plasma x-ray emissionusing charge-injection devices ~CIDs!, as has been demonstrated on the University of Rochester’s60-beam UV OMEGA laser facility @T. R. Boehly et al., Opt. Commun. 133, 495 ~1997!#. The CIDhas an architecture similar to a charge-coupled device. The differences make them more resistant toradiation damage and, therefore, more appropriate for some application in laser–plasma x-rayimaging. CID-recorded images have been obtained with x-ray pinhole cameras, x-ray microscopes,x-ray spectrometers, and monochromatic x-ray imaging systems. Simultaneous images obtained onthese systems with calibrated x-ray film have enabled determination of the absolute detectionefficiency of the CIDs in the energy range from 2 to 8 keV. © 2001 American Institute of Physics.@DOI: 10.1063/1.1318257#I. INTRODUCTIONX-ray imaging and x-ray spectroscopy are used in laser–plasma-generated physics research to diagnose conditions inlaser targets. Examples of techniques used to image x-rayemission are pinhole cameras, Kirkpatrick–Baez ~KB! mi-croscopes, curved crystal optics, and Wo¨lter microscopes.1–3All spectroscopic diagnostics also rely on spatial resolutionto record an x-ray spectrum. Examples of spectroscopic tech-niques are Bragg crystal diffraction and grating diffraction.The simplest method of recording images is by time-integrated exposure of film, a common example being thecalibrated Kodak direct exposure film ~DEF!.4 Alternatively,images can be recorded by a solid-state device that is eitherdirectly sensitive to x rays ~photons absorbed in the device!or indirectly sensitive ~photons absorbed in a phosphor coat-ing, generating visible-range photons that are then absorbedin the device!.The detectors investigated in this work are known ascharge-injection devices ~CIDs!, so named by the pixel ar-chitecture, and are used in the direct detection mode torecord x-ray images. The instrumentation and methods usedto interface CIDs to time-integrated x-ray diagnostics on theOMEGA UV laser facility5 are described in this work. Im-ages were obtained with pinhole cameras, KB microscopes,2and a tunable monochromatic x-ray microscope.6II. CHARGE-INJECTION DEVICES CIDSThe CID cameras used in this work are manufactured byCID Technologies, Inc., of Liverpool, NY.7 The modelCID4150 is an 8123604 array having square pixels with38.5 mm center-to-center spacing and overall array dimen-sions of 31.3323.2 mm. Details of the pixel architecture canbe found in the literature,8–11 summarized here as follows:Each pixel contains two storage areas ~pads!. At the start ofintegration, voltage applied to both pads injects any storedcharge into the substrate layer. Next, charge is accumulatedunder a negatively biased column storage pad until the biasis changed to transfer the stored charge to a row pad. Therow pad is attached to a row preamplifier from which thesignal is output and digitized. The CIDs used in this workwere operated at room temperature and with no conversionphosphor coating on the detector surface ~direct x-ray detec-tion!. A PC-based analog-to-digital converter with 16 bitresolution, operating at 500 kHz, accomplished the camerareadout. The relatively high-speed readout was employed tominimize dark current in the uncooled detectors.Figure 1 shows a CID camera in its housing and anepoxy-encased dental-imaging version,11 for comparison,along side a film pack and film-pack positioner, illustratingthe relative compactness of the CID camera. All signal am-plification and switching electronics are contained in the CIDcamera. An overview of the installation on the OMEGA tar-get chamber and surrounding structure is shown in Fig. 2.The DC power is supplied along with a clocking line and anintegration trigger line. The common integration trigger sup-plies each camera in use with a preshot pulse to acquire abackground image and an on-shot pulse to acquire an imageon the laser target shot. The two images are subtracted toprovide the final image. The single output line contains theunformatted video signal, which is sent to a PC-basedanalog-to-digital converter card. Up to two PCs are used toacquire six CID camera outputs per PC, on as many as 12CID cameras for the currently planned system.a!Electronic mail: fredm@lle.rochester.eduREVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 72, NUMBER 1 JANUARY 20017130034-6748/2001/72(1)/713/4/$18.00 © 2001 American Institute of PhysicsDownloaded 25 Oct 2006 to 129.21.183.26. Redistribution subject to AIP license or copyright, see http://rsi.aip.org/rsi/copyright.jspIII. EXPERIMENTSThe CID cameras were used to obtain images of laser–plasma x-ray emission on OMEGA. Three different diagnos-tics were used as platforms for these tests: x-ray pinholecameras and two different KB microscopes. One microscopewas outfitted with a grating and used to obtain grating-dispersed images of target implosion cores.12 The other mi-croscope was outfitted with metal multilayer monochroma-tors and used to obtain narrow-energy-band ~monochro-matic! x-ray images of target implosion cores.6Figure 3 shows two images obtained with pinhole cam-eras located on opposite sides of the target chamber. Thepinhole cameras have 11 mm pinholes and were located 170mm from the target. The CIDs were located to provide im-ages with a magnification of 4.0 ~;10 mm/pixel at the targetplane!. The images are of x-ray emission from a 4-mm-diam,Au-coated plastic sphere. The OMEGA beams were surfacefocused onto the target using the standard OMEGA opticsand distributed phase plates designed to produce Gaussian-like focal spots with a diameter of ;900 mm ~containing95% of the energy!. These produce x-ray spots with diam-eters of ;600 mm @full width at half maximum ~FWHM!#.The images are analyzed to determine the relative pointing ofeach beam compared to the desired pointing ~all beamspointed so as to converge at the target center, in thespherical-implosion-pointing mode!. Typically, six or morefilm-based cameras are used to obtain like images, necessi-tating film loading, unloading, developing, drying, and fi-nally digitizing. Although these processes are streamlined byusing autofilm developers, quick drying, and video cameradigitizing, the typical minimum processing time of ;40 mincannot compete with the several-minute time scale requiredto store and redisplay multiple digital image files.Another example of CID-camera-obtained x-ray imagesis shown in Fig. 4. The CIDs were located behind the samepinhole cameras described above, but further away at a mag-nification of 8.0. The images are of the time-integrated x-rayemission from an imploded laser fusion target ~in this case, a3-atm-D2-filled, 20-mm-thick CH shell!. Figure 4~a! wastaken with minimum filtration in front of the CID sensor~150 mm of Be, mostly in the pinhole camera itself!, whileFig. 4~b! was taken with a CID on a pinhole camera on theopposite side of the target chamber and additional filtrationof 50 mm of Al was used to limit the soft x-ray component ofthe image. Figure 4~a! clearly shows the target’s outer-shellemission plus stalk emission ~all of which occurs during tar-get acceleration!. Figure 4~b! shows only the harder x-rayemission that is confined to the high-density, high-temperature implosion core region.FIG. 1. Picture of CID camera mounted on the end of a pinhole camerapositioner. The CID camera replaces the film-pack holder ~upper left! andfilm pack ~lower left!. The CID camera was designed to be compact, asevidenced by the dental-imaging version ~lower right!.FIG. 2. Schematic of the CID camera interface to an OMEGA x-ray diag-nostic.FIG. 3. CID images taken from two opposing pinhole cameras on anOMEGA pointing shot.FIG. 4. CID images of a directly driven imploding OMEGA laser target~from opposing pinhole cameras!: ~a! soft x-ray image containing emissionfrom the outer shell region, the stalk, and a saturated core region; ~b! hardx-ray image containing only emission from the core.714 Rev. Sci. Instrum., Vol. 72, No. 1, January 2001 Marshall et al.Downloaded 25 Oct 2006 to 129.21.183.26. Redistribution subject to AIP license or copyright, see http://rsi.aip.org/rsi/copyright.jspPairs of images, one on film and one with a CID on thesame x-ray microscope, have been obtained on a series oftarget shots on OMEGA. The KB microscope was outfittedwith a diffraction grating that yielded dispersed spectra ofthe implosion cores.12 The magnification of the images is20.3. Since the KB microscope is a four-mirror, four-imageversion with image views separated by 1.4° on the targetchamber sphere, the images are nearly identical except fordifferences in the recording media. Figure 5 shows a pair ofsuch images: ~a! a film-recorded image ~Kodak DEF! and ~b!a CID-camera-recorded image. Both images are produced bythe KB microscope, which has Ir-coated mirrors operating atgrazing angles of 0.70°. Attenuation by 140 mm of Be iscommon to both, as is diffraction by the 0.2-mm-periodtransmission grating. The CID camera had an additional 25mm of Be acting as a light shield and housing cover. Bothimages show nearly identical features. The main featurescaptured by the grating-dispersed microscope ~zeroth-orderimage of implosion and first-order diffracted image of thecore! are seen in both images. Since the film and microscopehave been absolutely calibrated, comparison of the film- andCID-recorded core spectra can be used to infer the absolutesensitivity of the CID pixels. Figure 6~a! shows such a com-parison taken along the core spectrum and plotted as a func-tion of photon energy. The CID pixel’s inferred quantumefficiency dependence on energy is shown in Fig. 6~b!. Al-though a precise model for the CID pixels has not been de-veloped, the results of Janesick et al.13 for the case of afrontside-illuminated, thin-depletion-region charge-coupleddevice are shown for comparison in Fig. 6~b!. This modelshould closely represent the CID sensitivity.Finally, a pair of images taken with the KB microscopeoutfitted with metal multilayer monochromators is shown inFig. 7. The imaging system has been previously described.4WB4C multilayers with a 2d spacing of 26.5 Å were used,and the magnification of the images is 13.6. The monochro-mators were tuned so as to produce images of target emis-sion centered on the Ar He-like b line ~3.68360.011 keV!and the Ar H-like b line ~3.93560.012 keV!, where the in-dicated energy range is determined by the FWHMs of themonochromator diffraction peaks. The target was a 15 atm,D2-filled, 25-mm-thick, 1-mm-diam CH shell containing0.35% by atomic number of Ar gas as a dopant. The imagesshow the enhanced line-plus-continuum emission from theimplosion core region. The asymmetry of the core is ascribedto the lack of perfect direct-drive beam balance on this shot,aggravated by several lower-intensity beams being near eachother on the target chamber sphere. The images show a clearcore region whose size and morphology can be clearly mea-sured.IV. CONCLUSIONSCID cameras have been used to obtain time-integratedx-ray images on a variety of imaging and spectroscopic di-agnostics on the OMEGA laser facility’s target chamber.Cross calibration of the CID camera with film shows that theCID pixels, when used in direct-detection mode ~i.e., withouta phosphor!, have a useful energy range of better than 2–8keV, with additional sensitivity to be expected, especially atFIG. 5. Pair of simultaneously recorded x-ray microscope images taken with~a! Kodak DEF film and ~b! a CID camera. The image is an implodingOMEGA target with dispersion of the core emission by an x-ray transmis-sion grating ~evidenced by the features ;30° from the horizontal to theupper right and lower left!. The horizontal and vertical streaks are due tosmall-angle specular scattering from the microscope mirrors.FIG. 6. Comparison of CID- and film-recorded spectra. ~a! Lineouts throughthe two spectral features; ~b! inferred CID quantum efficiency, derived fromthe calibrated constants of the microscope/grating/film system.FIG. 7. Monochromatic images of an imploding OMEGA laser target takenwith two CID cameras.715Rev. Sci. Instrum., Vol. 72, No. 1, January 2001 Plasma diagnosticsDownloaded 25 Oct 2006 to 129.21.183.26. Redistribution subject to AIP license or copyright, see http://rsi.aip.org/rsi/copyright.jsphigher energies. Currently, all existing OMEGA time-integrated x-ray diagnostics are being outfitted with CIDcameras as an optional recording medium.ACKNOWLEDGMENTSThe authors acknowledge the support of the OMEGAlaser operations group, and the staff at the Laboratory forLaser Energetics of the University of Rochester. This workwas supported by the U.S. Department of Energy Office ofInertial Confinement Fusion under Cooperative AgreementNo. DE-FC03-92SF19460, the University of Rochester, andthe New York State Energy Research and Development Au-thority. The support of DOE does not constitute an endorse-ment by DOE of the views expressed in this article.1 J. A. Koch et al., Appl. Opt. 37, 1784 ~1998!.2 F. J. Marshall and Q. Su, Rev. Sci. Instrum. 66, 725 ~1995!.3 N. M. Ceglio, A. M. Hawryluk, and R. H. Price, Appl. Opt. 21, 3953~1982!.4 B. L. Henke, J. Y. Uejio, G. F. Stone, C. H. Dittmore, and F. G. Fujiwara,J. Opt. Soc. Am. B 3, 1540 ~1986!.5 T. R. Boehly et al., Opt. Commun. 133, 495 ~1997!.6 F. J. Marshall and J. A. Oertel, Rev. Sci. Instrum. 68, 735 ~1997!.7 CID Technologies, Inc., 101 Commerce Blvd., Liverpool, NY 13088.8 Z. Ninkov, C. Tang, and R. L. Easton, Proc. SPIE 2172, 180 ~1994!.9 J. Zarnowski, J. Carbone, R. Carta, and M. Pace, Proc. SPIE 2172, 187~1994!.10 J. Carbone, J. Zarnowski, M. Pace, S. Czebiniak, and R. Carta, Proc. SPIE2654, 131 ~1996!.11 J. Carbone, Z. Alam, C. Borman, S. Czebiniak, and H. Ziegler, Proc. SPIE3301, 90 ~1998!.12 F. J. Marshall, J. A. Delettrez, R. Epstein, and B. Yaakobi, Phys. Rev. E49, 4381 ~1994!.13 R. J. Janesick, T. Elliott, S. Collins, T. Daud, D. Campbell, and G.Garmire, Opt. Eng. ~Bellingham! 26, 156 ~1987!.716 Rev. Sci. Instrum., Vol. 72, No. 1, January 2001 Marshall et al.Downloaded 25 Oct 2006 to 129.21.183.26. Redistribution subject to AIP license or copyright, see http://rsi.aip.org/rsi/copyright.jsp

Imaging of Laser-Plasma X-ray Emission with Charge-Injection Devices

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Imaging of Laser-Plasma X-ray Emission with Charge-Injection Devices

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