K-shell emission x-ray imaging of z-pinch plasmas with a pinhole and a logarithmicspiral crystalQingguo Yang, Zeren Li, Qixian Peng, Libing Yang, Guanhua Chen, Yan Ye, Xianbin Huang, Hongchun Cai,Jing Li, and Shali Xiao Citation: Review of Scientific Instruments 82, 093301 (2011); doi: 10.1063/1.3634002 View online: http://dx.doi.org/10.1063/1.3634002 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/82/9?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Multicolor, time-gated, soft x-ray pinhole imaging of wire array and gas puff Z pinches on the Z and Saturn pulsedpower generatorsa) Rev. Sci. Instrum. 79, 10E906 (2008); 10.1063/1.2969280 Monochromatic Soft XRay SelfEmission Imaging in Dense Z Pinches AIP Conf. Proc. 926, 229 (2007); 10.1063/1.2768855 One- and two-dimensional modeling of argon K-shell emission from gas-puff Z-pinch plasmas Phys. Plasmas 14, 063301 (2007); 10.1063/1.2741251 Multilayer mirror monochromatic self-emission x-ray imaging on the Z accelerator Rev. Sci. Instrum. 77, 10E316 (2006); 10.1063/1.2220071 Soft x-ray (0.2 keV ) imager for z -pinch plasma radiation sources Rev. Sci. Instrum. 75, 4026 (2004); 10.1063/1.1787903

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

146.189.194.69 On: Fri, 19 Dec 2014 18:55:50

REVIEW OF SCIENTIFIC INSTRUMENTS 82, 093301 (2011)

K-shell emission x-ray imaging of z-pinch plasmas with a pinholeand a logarithmic spiral crystal

Qingguo Yang,1,a) Zeren Li,1 Qixian Peng,1 Libing Yang,1 Guanhua Chen,1 Yan Ye,1

Xianbin Huang,1 Hongchun Cai,1 Jing Li,1 and Shali Xiao2

1Institute of Fluid Physics, CAEP, Mianyang, Sichuan 621900, People’s Republic of China2The Key Laboratory of Optic-electronic Technology and System, Ministry of Education, Chongqing University,Chongqing 400044, People’s Republic of China

(Received 2 June 2011; accepted 17 August 2011; published online 12 September 2011)

An in-chamber, mini x-ray imaging instrument employs a pinhole and a logarithmic spiral crystalhas been developed for obtaining K-shell line images of the imploding aluminum wire array on the“Yang” accelerator. The logarithmic spiral crystal acts as a monochromator and a non-dispersive mir-ror that reflects the pinhole image to a x-ray film detector with a very narrow photon energy bandwidth(<1 eV, mainly determined by the width of rocking curve of the crystal). Two imaging configurationswith the use of Quartz (101̄0) crystal and Mica (002) crystal are designed, respectively, to imagethe Al Lyα2 line (1727.7 eV) emission and Al Heα intercombination line (1588.3 eV) emission. Theprimary experimental data corresponding to these two configurations are presented and discussed.© 2011 American Institute of Physics. [doi:10.1063/1.3634002]

I. INTRODUCTION

Fast Z-pinches are powerful and efficient soft x-ray ra-diators are used for research in inertial confinement fusion,radiation physics, laboratory astrophysics, and other high en-ergy density sciences.1 As the Z-pinch plasma generates co-pious x rays in a very wide spectral range from several hun-dreds eV to several hundreds keV, the x-ray spectroscopy,2–7

the x-ray self-emission imaging,8–13 or their combination, saythe x-ray imaging spectroscopy,14–23 provide natural diagnos-tic tools for studying Z-pinch physics. X-ray spectroscopyand x-ray self-emission imaging can only provide the sim-plex spectral or spatial information of the plasmas, while thex-ray imaging spectrograph based on bent crystal can simul-taneously give both in a single shot, and thus has been widelyused in the high energy density physics community. However,due to the contradiction of the availability of spatial resolutionand spectral resolution in an imaging spectrograph, it can-not provide more details of the plasma’s structure informationfor every spectral lines. In some cases, the detailed investiga-tion of the plasma’s conformation with high spatial resolutionat interested spectral band or spectral lines becomes desir-able and much valuable. For this reason, many narrowbandor quasi-monochromatic x-ray imaging techniques have beensuccessfully developed for Z-pinch plasma measurement, in-cluding the use of a filtered pinhole camera combined with agrazing incidence reflection mirror9, 10 or a planar multilayermirror.11–13 However, these techniques are mainly used to im-age the continuous spectrum with photon energy less than1.5 keV and might be unfeasible when the instrument is keyedto image the (1–10) keV K-shell emission due to the inherentconstraints, such as limited mirror-filter match and/or largeenergy dispersion. The K-shell images are helpful for under-

a)Author to whom correspondence should be addressed. Electronic mail:yungore@163.com.

standing the z-pinch physics and can be used to retrieve thetemperature and density maps of the plasma.24, 25

In Ref. 26, we have proposed a monochromatic x-ray im-ager which employs a pinhole and a logarithmic spiral crystalto achieve a very narrow energy bandwidth. Here, we reporton the realization of this imager: an in-chamber, mini instru-ment presently implemented on the “Yang” accelerator to im-age the aluminum K-shell line images. In Sec. II, the imaginggeometry is briefly described. In Sec. III, the instrument de-sign and the experimental imaging data are presented. Thesummary and future applications are discussed in Sec. IV.

II. IMAGING GEOMETRY

The instrument described here employs a pinhole and alogarithmic spiral cylindrically bent crystal. As is shown inFig. 1, the pinhole images the plasmas on the logarithmic spi-ral crystal, and the crystal reflects this image onto the detector.The imaging geometry in the x-o-y plane (the plane includesthe center of plasma, the pinhole, and the center of crystal; thez axis is perpendicular to this plane) is shown in Fig. 2. As iswell known, a logarithmic spiral has the defining characteris-tic that all lines from a focal point (where a pinhole is located)meet the spiral at the same angle.27, 28 Therefore, the logarith-mic spiral crystal reflects only one monochromatic beam withwavelength satisfying the Bragg equation. The surface of thelogarithmic spiral crystal can be described by the followingequation:

r (ϕ, δ) = dceϕ cot θ

cos δ,(

−ϕ0 ≤ ϕ ≤ ϕ0,−W

2≤ r (ϕ, δ) sin δ ≤ W

2

), (1)

where ϕ0 = tan θ log{(2dc)−1[L cos θ+(4dc2+L2 cos2 θ )1/2]},

θ is the Bragg grazing angle, dc is the distance of pinhole tocrystal center, L is the crystal length, and W is the crystal

0034-6748/2011/82(9)/093301/5/$30.00 © 2011 American Institute of Physics82, 093301-1

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

146.189.194.69 On: Fri, 19 Dec 2014 18:55:50

093301-2 Yang et al. Rev. Sci. Instrum. 82, 093301 (2011)

FIG. 1. (Color online) Schematic shown of the monochromatic x-ray imager.

width. If the object plane is assumed to be parallel with y axisand the image plane is assumed to be parallel with x axis asshown in Fig. 2, by using ray tracing calculations, the objectpoint (yo, zo) related with the image point (xi , zi ) by{

yo = −do tan ϕ,

zo = −do sec ϕ tan δ,(2)

{xi = dceϕ cot θ csc(2θ + ϕ) sin 2θ + di cot(2θ + ϕ),

zi = csc(2θ + ϕ)[2dceϕ cot θ cos(θ + ϕ) sin θ + di ] tan δ,

(3)where do and di are, respectively, the distance of object planeto y axis and the distance of image plane to x axis. A generaltheory model that the object plane and the image plane arenot always parallel to the x axis or the y axis can be found inRef. 26 and here we simplified the model. The formulas forcalculating the performance parameters of the imaging sys-tem can be deduced from the basic relationships presented inEqs. (2) and (3), and are listed in Table I. It should be noticedthat the magnification, the field of view, and the spatial reso-lution are different in two independent directions and shouldbe considered, respectively.

III. MINI INSTRUMENT DESIGNAND EXPERIMENTAL DATA

The instrument presently implemented on the “Yang” ac-celerator is intended for imaging the K-shell emission of animploding wire array. The instrument is designed to have highsensitivity and compact size by installing the whole imager inthe chamber and moving the pinhole and detector in as closeto the target as possible, limited by interference with other di-

x

y

oϕ

θ

θ

Object plane

Image plane

Pinhole

Logarithmicspiral crystal

FIG. 2. (Color online) Imaging geometry of the monochromatic x-ray im-ager.

x

y

o

θ

θϕ

Δθ1

Δθ2

Δϕ1

Δϕ2

Mm(ϕ)σmGeo

FIG. 3. (Color online) Schematic shown of the spatial resolution in the x axisdirection is limited by a pinhole with finite size.

agnostic beams. The hardware design layout for this imager isshown in Fig. 4. The imager includes a pinhole, a logarithmicspiral crystal, a film detector, and other mechanical compo-nents. The key problem of this instrument is the alignmentof the pinhole and the crystal. According to the imaging ge-ometry, the pinhole and the crystal must be positioned accu-rately in order to achieve a narrow bandwidth. This problemis solved by manufacturing a metal template, on which a 1:1pattern of optical path is engraved for assistant of the posi-tioning of the crystal. The dimensions of the imager’s box arenot to exceed 160 mm ×85 mm × 70 mm.

Two configurations are presently designed to image theK-shell emission of an imploding aluminum wire array andthe parameters of them are listed in Table II. Configuration(a) aims at imaging the Al Lyα2(2p1/2 − 1s1/2) line by using aQuartz (101̄0) crystal and configuration (b) aims at the Al Heα

intercombination line (1s2p 3 P1 − 1s2 1S0) by using a Mica(002) crystal with second diffraction order. The raw exampleimages acquired by this imager corresponding to configura-tions (a) and (b) are shown in Fig. 5. The images are recordedby a Kodak BioMax MS film shielded by a 20 μm Be fil-ter, and a 6 mm diameter array with 8 aluminum wires of25 μm diameter, 15 mm long and 0.02 mg mass is used toproduce the K-shell emissions. The images are distorted andhave astigmatism aberrations because the magnifications inthe x axis direction and in the z axis direction are different and

FIG. 4. The hardware design layout for the monochromatic imager.

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

146.189.194.69 On: Fri, 19 Dec 2014 18:55:50

093301-3 Yang et al. Rev. Sci. Instrum. 82, 093301 (2011)

TABLE I. The formulas of the performance parameters for monochromatic x-ray imaging system.

Performance parameters FormulasMagnification Mx (ϕ) = d−1

o cos2 ϕ csc2(2θ + ϕ)[di − 2dceϕ cot θ cos θ sin(θ + ϕ)]Mz(ϕ) = −d−1

o cos ϕ csc(2θ + ϕ)[di + 2dceϕ cot θ sin θ cos(θ + ϕ)]Field of view Fy = 2do tan ϕ0

Fz = doW d−1c e−ϕ cot θ

Spatial resolutiona σ = [σ 2Geo + (2.44λdo/D)2]1/2

σ zGeo = [Mz(ϕ) + 1]Mz(ϕ)−1 D

σ xGeo = |Mx (ϕ)−1[ f (ψ2, ϑ2) − f (ψ1, ϑ1)]|

Energy bandwidthb ERC = −E cot θθRC

EWidth = E(1 − cos δ)Imaging efficiencyc η = π D2ηc[4Mx (ϕ)Mz(ϕ)d2

o ]−1

aThe spatial resolution includes the geometric and diffractive contributions. D is the pinhole diameter, λ is the x-ray wavelength.f (ψ, ϑ) = dceψ cot θ csc(2ϑ + ψ) sin 2ϑ + di cot(2ϑ + ψ), ψ1 = ϕ − ϕ1, ψ2 = ϕ + ϕ1, ϑ1 = θ − θ1, ϑ2 = θ + θ2, and(ϕi ,θi )i=1,2 are the angles labeled in Fig. 3.bThe photon energy bandwidth mainly includes the contributions from the width of rocking cure, θRC, of the bent crystal andfrom the energy dispersion across the crystal surface due to finite width of the plasma in the z axis direction.cηc is the crystal related efficiency (Ref. 29).

vary with angle ϕ. However, since an implicit expression forthe transformation between the object plane and image planeis known, one can use a digital image processing method torestore the correct image. The pinhole diameter is a key pa-rameter that should be optimized to balance the spatial resolu-tion and the image exposure. In configuration (a), a pinhole of100 μm diameter is adopted to win a good spatial resolu-tion and image exposure, while in configuration (b), a pin-hole of 300 μm diameter is used in order to obtain an ac-

ceptable image for the sake of weak line emission and lowintegral reflectivity of mica crystal. From the calculationsshown in Table II, the photon energy bandwidth of thisimaging system does not exceed 1 eV and is mainly de-termined by the width of rocking curve of the bent crys-tal. For a practical crystal, the width of rocking curvemight be greater than the theoretical calculations in the(1–10) keV range, but is still under the level of emissionlinewidth.

FIG. 5. (Color online) Raw images (false-color) acquired by the monochromatic imager corresponding to configurations (a) (shot 1203) and (b) (shot 1200).The dimensions of the effective image region divide the magnification accords with the actual plasmas size.

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

146.189.194.69 On: Fri, 19 Dec 2014 18:55:50

093301-4 Yang et al. Rev. Sci. Instrum. 82, 093301 (2011)

TABLE II. The parameters for the monochromatic imager implemented onthe “Yang” accelerator.

A B

Designed parametersEmission line Al Lyα2 Al Heα

Photon energy E (eV) 1727.7 1588.3Crystal Quartz 101̄0 Mica 002Diffraction order 1 2Bragg angle θ (◦) 57.46 51.90Crystal length L (mm) 40 40Crystal width W (mm) 15 15Pinhole diameter D (μm) 100 300Object plane to y axis distance do (mm) 100 134Image plane to x axis distance di (mm) 31 31Pinhole to crystal center distance dc (mm) 120 120

Calculated parameters (Averaged)Magnification

in x axis direction 0.95 0.68in z axis direction 1.54 1.13

Field of view (mm)in y axis direction 28 35in z axis direction 11.5 15

Spatial resolution (μm)in x axis direction 97 391in z axis direction 165 564

Energy bandwidth (eV)Contributions from plasma’s widtha 0.19 0.1Contributions from width of rockingcurveb

0.15 0.31

Efficiency 3.03 × 10−10 6.25 × 10−10

aIf the plasma’s width is assumed to be 3 mm.bThe width of rocking curve and the integrated reflectivity are computed by the XOPcode (Ref. 30).

The images in Fig. 5 show the K-shell emissions ofimploding aluminum wire array are nonuniform distributedalong the axial direction caused by the magnetic Rayleigh-Taylor instabilities. The multi-bright spots in the figure showthe plasma region around these spots are very hot and dense.

FIG. 6. (Color online) Pinhole images (pinhole diameter is 50 μm, Spectralband is greater than 1.0 keV and the magnification is 0.5) for shot 1203 (up)and shot 1200 (down).

Compared with the 50 μm diameter pinhole images filteredby 20 μm Be of the z-pinch plasmas with continuous spec-trum (>1.0 keV) as is shown in Fig. 6, the K-shell imageseliminate most of the background radiations so that it can givemore information about the driven capability of the pulser andthe conversion efficiency of the electric energy to K-shell ra-diant energy. The K-shell image of a good pinched plasma isenvisaged that the distribution of the emission are continuousand uniform along the axial direction and the images shownin Fig. 5 do not meet this criterion.

IV. CONCLUSIONS AND DISCUSSION

A monochromatic x-ray imager employs a pinhole anda logarithmic spiral crystal has been developed for measur-ing the K-shell emission images of the imploding aluminumwire array on the “Yang” accelerator. The imager has the ad-vantage of simple structure, compact size, and excellent pho-ton energy bandwidth. The imager has successfully been ap-plied to obtain the aluminum z-pinch plasma images at AlLyα2 line (1727.7 eV) and at Al Heα intercombination line(1588.3 eV).

The main limitation of this instrument is the achievableimage exposure, due to pinhole imaging constraints com-pounded by spectral elimination from crystal. The constraintbecomes particularly severe when a low integral-reflectivitycrystal is used and a weak line is aimed. Therefore, a high sen-sitivity detector, such as the imaging plate or the x-ray CCD,should be used to complement the reduction of available pho-tons when a very small pinhole is adopted in order to improvethe spatial resolution.

At present, only one frame image is acquired in a shot,but a dual or multichannel imaging system, which can acquiredouble or multiframe images with different photon energy ina shot, is much valuable. The future works include construct-ing such a diagnostic system for the plasma temperature anddensity maps retrieval, and coupling it with a gated micro-channel plate detector to give temporal resolution.

ACKNOWLEDGMENTS

The authors would like to thank many technicians andengineers of the “Yang” accelerator operating team for theirtechnical support. This work was supported by the Foundationof CAEP under Grant No. 2010B0401050.

1M. K. Matzen, M. A. Sweeney, R. G. Adams, J. R. Asay, J. E. Bailey,G. R. Bennett, D. E. Bliss, D. D. Bloomquist, T. A. Brunner, R. B.Campbell, G. A. Chandler, C. A. Coverdale, M. E. Cuneo,J. P. Davis, C. Deeney, M. P. Desjarlais, G. L. Donovan, C. J. Garasi,T. A. Haill, C. A. Hall, D. L. Hanson, M. J. Hurst, B. Jones, M. D.Knudson, R. J. Leeper, R. W. Lemke, M. G. Mazarakis, D. H. McDaniel,T. A. Mehlhorn, T. J. Nash, C. L. Olson, J. L. Porter, P. K. Rambo,S. E. Rosenthal, G. A. Rochau, L. E. Ruggles, C. L. Ruiz, T. W. L.Sanford, J. F. Seamen, D. B. Sinars, S. A. Slutz, I. C. Smith, K. W. Struve,W. A. Stygar, R. A. Vesey, E. A. Weinbrecht, D. F. Wenger, and E. P. Yu,Phys. Plasmas 12, 055503 (2005).

2J. E. White, Rev. Sci. Instrum. 21, 629 (1950).3L. S. Birks, Rev. Sci. Instrum. 41, 1129 (1970).4W. Swartz, S. Kastner, E. Rothe, and W. Neupert, J. Phys. B 4, 1747 (1971).5J. W. Criss, Appl. Spectrosc. 33, 19 (1979).

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

146.189.194.69 On: Fri, 19 Dec 2014 18:55:50

093301-5 Yang et al. Rev. Sci. Instrum. 82, 093301 (2011)

6K. Hirano, N. Nisatome, T. Yamamoto, and K. Shimoda, Rev. Sci. Instrum.65, 3761 (1994).

7T. Yanagidaira, K. S. Yasushi Ono, and K. Hirano, Rev. Sci. Instrum. 71,88 (2000).

8T. J. Nash, M. S. Derzon, G. A. Chandler, D. L. Fehl, R. J. Leeper,J. L. Porter, R. B. Spielman, C. Ruiz, G. Cooper, J. McGurn, M. Hurst,D. Jobe, J. Torres, J. Seaman, K. Struve, S. Lazier, T. Gilliland, L. A.Ruggles, W. A. Simpson, R. Adams, J. A. Seaman, D. Wenger, D. Nielsen,P. Riley, R. French, B. Stygar, T. Wagoner, T. W. L. Sanford, R. Mock,J. Asay, C. Hall, M. Knudson, J. Armijo, J. McKenney, R. Hawn,D. Schroen-Carey, D. Hebron, T. Cutler, S. Dropinski, C. Deeney, P. D.LePell, C. A. Coverdale, M. Douglas, M. Cuneo, D. Hanson, J. E. Bailey,P. Lake, A. Carlson, C. Wakefield, J. Mills, J. Slopek, T. Dinwoodie, andG. Idzorek, Rev. Sci. Instrum. 72, 1167 (2001).

9D. F. Wenger, D. B. Sinars, K. L. Keller, R. A. Aragon, L. E. Ruggles,W. W. Simpson, P. H. Primm, and J. L. Porter, Rev. Sci. Instrum. 75, 3983(2004).

10B. H. Failor, N. Qi, J. S. Levine, H. Sze, and E. M. Gullickson, Rev. Sci.Instrum. 75, 4026 (2004).

11B. Jones, C. Deeney, C. A. Coverdale, C. J. Meyer, and P. D. LePell, IEEETrans. Plasma Sci. 34, 213 (2006).

12B. Jones, C. Deeney, A. Pirela, C. Meyer, D. Petmecky, P. Gard, R. Clark,and J. Davis, Rev. Sci. Instrum. 75, 4029 (2004).

13B. Jones, C. Deeney, C. Meyer, and P. D. LePell, Rev. Sci. Instrum. 77,10E316 (2006).

14S. A. Pikuz, D. B. Sinars, T. A. Shelkovenko, K. M. Chandler, D. A.Hammer, G. V. Ivanenkov, W. Stepniewski, and I. Yu Skobelev, Phys. Rev.Lett. 89, 035003 (2002).

15S. A. Pikuz, T. A. Shelkovenko, M. D. Mitchell, K. M. Chandler, J. D.Douglass, R. D. McBride, D. P. Jackson, and D. A. Hammer, Rev. Sci.Instrum. 77, 10F309 (2006).

16S. A. Pikuz, J. D. Douglass, T. A. Shelkovenko, D. B. Sinars, andD. A. Hammer, Rev. Sci. Instrum. 79, 013106 (2008).

17M. Bitter, K. W. Hill, B. Stratton, A. L. Roquemore, D. Mastrovito,S. G. Lee, J. G. Bak, M. K. Moon, U. W. Nam, G. Smith, J. E. Rice,P. Beiersdorfer, and B. S. Fraenkel, Rev. Sci. Instrum. 75, 3660 (2004).

18B. F. K. Young, A. L. Osterheld, D. F. Price, R. Shepherd, R. E. Stewart,A. Ya. Faenov, A. I. Magunov, T. A. Pikuz, I. Yu. Skobelev, F. Flora, S.Bollanti, P. Di Lazzaro, T. Letardi, A. Grilli, L. Palladino, A. Reale,A. Scafati, and L. Reale, Rev. Sci. Instrum. 69, 4049 (1998).

19J. Workman and G. A. Kyrala, Rev. Sci. Instrum. 72, 674 (2001).20B. M. Song, S. A. Pikuz, T. A. Shelkovenko, K. M. Chandler,

M. D. Mitchell, and D. A. Hammer, Rev. Sci. Instrum. 74, 1954 (2003).21T. A. Shelkovenko, D. A. Chalenski, K. M. Chandler, J. D. Douglass,

J. B. Greenly, D. A. Hammer, B. R. Kusse, R. D. McBride, and S. A. Pikuz,Rev. Sci. Instrum. 77, 10F521 (2006).

22D. B. Sinars, D. F. Wenger, K. L. Keller, G. A. Rochau, and J. L. Porter,Rev. Sci. Instrum. 77, 10F327 (2006).

23D. F. Wenger, D. B. Sinars, G. A. Rochau, J. E. Bailey, and J. L. Porter,A. Ya. Faenov, T. A. Pikuz, and S. A. Pikuz, Rev. Sci. Instrum. 77, 10F312(2006).

24I. Uschmann, E. Forster, H. Nishimura, K. Fujita, Y. Kato, and S. Nakai,Rev. Sci. Instrum. 66, 734 (1995).

25Y. Ochi, I. Golovkin, R. Mancini, I. Uschmann, A. Sunahara, H. Nishimura,K. Fujita, S. Louis, M. Nakai, H. Shiraga, N. Miyanaga, H. Azechi,R. Butzbach, E. Forster, J. Delettrez, J. Koch, R. W. Lee, and L. Klein,Rev. Sci. Instrum. 74, 1683 (2003).

26Q. Yang, Z. Li, Q. Peng, G. Chen, X. Huang, H. Cai, and J. Li, Nucl. In-strum. Methods A 606, 320 (2009).

27G. Khelashvili, I. Ivanov, T. I. Morrison, G. Bunker, and D. Chapman, Rev.Sci. Instrum. 73, 1534 (2002).

28B. W. Adams and K. Attenkofer, Rev. Sci. Instrum. 79, 023102 (2008).29J. A. Koch, O. L. Landen, T. W. Barbee, J. P. Celliers, L. B. Da Silva,

S. G. Glendinning, B. A. Hammel, D. H. Kalantar, C. Brown, J. Seely,G. R. Bennett, and W. Hsing, Appl. Opt. 37, 1784 (1998).

30M. Sánchez del Río and R. J. Dejus, Proc. SPIE. 3448, 340 (1998).

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

146.189.194.69 On: Fri, 19 Dec 2014 18:55:50