Efficient light sources at BEUV & water

window soft x-ray wavelengths

Utsunomiya University, Japan

Takeshi Higashiguchi

Coauthors & CollaboratorsYuhei Suzuki, Masato Kawasaki, Hayato Ohashi,Nobuyuki NakamuraRyoichi Hirose, Takeo EjimaWeihua JiangTaisuke Miura, Akira EndoChihiro SuzukiKentaro Tomita, Daisuke Nakamura, Akihiko Takahashi, Tatsuo OkadaMasaharu Nishikino Shinsuke Fujioka, Kensuke Yoshida, Teruyuki Ugomori, Nozomi Tanaka, Hiroaki Nishimura Atsushi SunaharaShuichi Torii, Tetsuya MakimuraScally Enda, Bowen Li, Colm O’Gorman, Thomas Cummins, Takamitsu Otsuka, Deirdre Kilbane, Rebekah D’Arcy, Padraig Dunne, Gerry O'Sullivan

Acknowledgments: Thanks a million!!!

Recent progress in Utsunomiya, Japan

- 13.5-nm microplasma high brightness source

- simulation to evaluate plasma parameter & spectra

- seed beam at 10.6 μm for ps-CO2 pulse

- 6.x nm & WW incoherent radiation by various elements

- x-ray microscope

!λ (nm)

!λ (nm)

2 4

2 4

(a) Line spectrum

(b) UTA

Sn V Sn VI Sn VII Sn VIII Sn IX Sn X Sn XI Sn XII Sn XIII Sn XIV0

20

40

60

80

100

120

Energ

y (

eV

)

Scheme for high-energy emission: unresolved transition array

Peak wavelength of UTA emission

2

3

4

5

6

7

8

9

10

60 65 70 75 80 85

Peak WL w/ ns-laser_180Peak WL w/ ps-laser_99

Peak

wav

elen

gth

(nm

)

Atomic number

Gd

TbRe

Pt

BiAu

Pb4.5 nm W

Ta

Er

0 1 2 3 4 5 6 7 8

Inte

nsity

/ Q

E (a

rb. u

nits

)

Wavelength (nm)

ns-laser_180

83Bi

82Pb

79Au

78Pt

75Re

65Tb

64Gd

74W

73Ta

68Tb

0 1 2 3 4 5 6 7 8

Inte

nsity

/ Q

E (a

rb. u

nits

)

Wavelength (nm)

ps-laser_99

83Bi

82Pb

79Au

78Pt

75Re

65Tb

64Gd

74W

73Ta

68Tb

laser wavelength: 1064 nmpulse duration: 10 ns (blue) 150 ps (red)

Sn plasma & Mo/Si @ 13.5 nm

ArF laser @ 193 nm

? & ? @ ? nm

G. Tallents et al., Nature Photonics 4, 809 (2010).

Beyond EUV at 6.x nm

6.0 6.5 7.0 7.5 8.00

70

70

70

70

70

70

70Gd12+

Gd13+

Gd14+

Gd15+

Gd16+

Gd17+

Gd18+

Wavelength (nm)

gf

6.0 6.5 7.0 7.5 8.00

35

35

35

35

35

35

35Gd19+

Gd20+

Gd21+

Gd22+

Gd23+

Gd24+

Gd25+

Wavelength (nm)

T. Otsuka et al., Appl. Phys. Lett. 97, 111503 (2010). B. Li et al. Appl. Phys. Lett. 99, 231502 (2010).

Rare-earth: Gd for 6.x nm

Charge separated spectra of Gd ions by E-BITExpt.! Calc. !

H. Ohashi et al. (to be published)

[Kr] 4d10

[Kr] 4d

Charge-defined emission spectra with FAC for 4d-4f transitions!

Summary in 2 years: 6.x-nm Beyond EUV sources

0

0.1

0.2

0.3

0.4

0.5

1011 1012 1013 1014 1015 1016

Con

vers

ion

effic

ienc

y (%

)at

6.7

nm

in 0

.6%

BW

and

2π

sr

Laser intensity (W/cm2)

nspsfs

0

0.1

0.2

0.3

0.4

0.5

0.6

Con

vers

ion

effic

ienc

y (%

)at

6.7

nm

in 0

.6%

BW

and

2 s

r

109 1010 1011

Laser intensity (W/cm2)1012

I.!/ D I0.!/e!!n`` ! cS !LAPL 99, 191502 (2011).

0

50

100

150

200

250

300

350

5.5 6 6.5 7 7.5 8 8.5 9 9.5 10

Inte

nsity

(arb

. uni

ts)

Wavelength (nm) APL 99, 231502 (2010).

APL 100, 061118 (2012).

low density target DPP CO2 LPP

ps LPP

0

50

100

150

200

250

300

5.5 6 6.5 7 7.5 8 8.5 9 9.5 10

Inte

nsity

(arb

. uni

ts)

Wavelength (nm)

1064 nm532 nm355 nm

Laser

10.1117/2.1201109.003765

Shorter-wavelength extreme-UVsources below 10nmTakeshi Higashiguchi, Takamitsu Otsuka, Noboru Yugami,Weihua Jiang, Akira Endo, Padraig Dunne, Bowen Li, andGerry O’Sullivan

A next-generation laser-produced plasma system based on rare-earthtargets generates strong resonant line emissions at 6.5–6.7nm.

In recent years, laser-produced dense plasmas have been attract-ing attention as high-efficiency, high-power sources of extremeUV (EUV) radiation. Sources with a wavelength less than 10nmare of particular interest for use in next-generation semiconduc-tor lithography and for other applications, such as materials sci-ence and biological imaging. Manufacturer Cymer, for example,has already shipped a high-average-power 13.5nm engineer-ing prototype to a semiconductor device company that wouldenable high-volume production at a power level of 80W.1 Thissource optimizes unresolved transition array (UTA) emission ofhighly ionized tin for high conversion efficiency (CE) of the in-put laser energy to the in-band (i.e., a bandwidth of about 2%around 13.5nm) EUV energy. Full recovery of the injected fuel isrealized through ion deflection in a magnetic field. Low-densitytargets like tin further enable suppression of satellite (i.e., peri-pheral) emission. Full ionization, which helps to control debrisand thus avoid damage to the source mirror, is attained withshort-pulse CO2 laser irradiation.

Recently, the possibility of switching to an even shorterEUV wavelength of 6.Xnm was suggested.2 In fact, 6.Xnmbeyond-EUV (BEUV) emission can be coupled with a molyb-denum/boron carbide (Mo/B4C) or lanthanum/boron carbide(La/B4C) multilayer mirror whose reflectivity is currently 40%at 6.5–6.7nm (theoretical maximum >70%). The UTA emissionexploited in tin is scalable to shorter wavelengths. The rare-earth element gadolinium (Gd) has a CE similar to that of tin,though at a higher plasma temperature, within a narrow spectralrange centered near 6.7nm. However, no fundamental researchhas been reported on spectral behavior at 6.7nm and its depen-dence on various parameters, such as laser wavelength, initialtarget density, and dual-laser-pulse delay. EUV emission at thislevel could be tuned for use with a Mo/B4C multilayer mirrorto power practical sources.

Figure 1. Electron temperature dependence of the gadolinium (Gd) ionpopulation according to the steady-state collisional-radiative model (a).The weighted oscillation strength (gf) spectra of the resonant lines foreach contributing ion stage are shown in (b) and (c).

In a proof-of-principle experiment, we produced a source withpeak emission around 6.5–6.7nm.3, 4 gadolinium and terbium(another rare-earth element) produce strong narrow-band emis-sion, again attributable to thousands of resonance lines that

Continued on next page

APL 97, 231503 (2010).

0

0.2

0.4

0.6

0.8

1.0

1.2

5 5.5 6 6.5 7 7.5 8 8.5 9

Inte

nsity

(arb

. uni

ts)

Wavelength (nm)5 5.5 6 6.5 7 7.5 8 8.5 9

Wavelength (nm)

GdTb

APL 97, 111503 (2010).

Self-absorption Spectral structure

Peak wavelength

0

0.1

0.2

0.3

0.4

0.5

0.6

-100 -50 0 50 100 150 200Pulse separation time (ns)

Con

vers

ion

effic

ienc

y (%

)at

6.7

nm

in 0

.6%

BW

and

2π

sr

Laser intensityPrepulse: 1.0 x 1011 W/cm2

Main pulse: 5.6 x 1012 W/cm2

APL 100, 141108 (2012).APL 101, 013112 (2012).

CO2Nd:YAG

1010 1011 1012 10130

0.2

0.4

0.6

0.8

1

Laser intensity (W/cm2)

Conv

ersio

n ef

ficie

ncy

(%)

3 4 5 6 7 8 9 10 11 120

0.2

0.4

0.6

0.8

1

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

3 4 5 6 7 8 9 10 11 120

0.2

0.4

0.6

0.8

1

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

Opt. Exp. (accepted).

Database experiment by GEKKO XII

SphericalPlanar

Polystyrene*φ50

*φ500*µm

*

Target*material*(Gd,*Tb,*Mo)*2*µm*coa=ng

support

Laser*beams*(λ=1.053*µm)@1011~1014*W/cm2**1.3*ns*

EUV$pinhole$camera$images$at$6.7$nm$with$0.6%BW$from$Gd$plasmas$(magnifica)on:,x,5.7),,Zr,filter,+,La/B4C,mirror,

650µm

φ500µm

1E+12,W/cm2

φ300µm

500µm

3E+12,W/cm2

φ100µm

150µm

3E+13,W/cm2

450µm

φ200µm

7E+12,W/cm2

stoke

120µm

φ50µm

1E+14,W/cm2

Spectra & CEs in GEKKO XII exp

6.7$nm6.5$nm

Gd#/#Tb#/#Mo#plasma#spectra1.0

0.8

0.6

0.4

0.2

Inte

nsity

[a.u

.]

121086

Wavelength [nm]

GdMoTb

[@1012 W/cm2]

0.8

0.6

0.4

0.2

0.0Co

nver

sion

Effic

ienc

y(%

)

2 3 4 5 61012

2 3 4 5 61013

2 3 4

Laser Intensity(W/cm)

Tb Gd Mo

Laser intensity (W/cm2)

Electron density profile

1018

2

3

4

5

6

789

1019

2

3

4

5

Ele

ctro

n de

nsity

[cm

-3]

10008006004002000

Distance [µm]

1.0

0.8

0.6

0.4

0.2

0.0

Intensity [a.u.]

Gdø500 µm 1x1012

W/cm2

Gdø200 µm 7x1012

W/cm2

Gd ø50 µm 1x1014

W/cm2

7×1012&W/cm2

1×1012&W/cm2

1×1014&W/cm2

Requirement in high-Z plasma UTA with high CE

Optically thin plasmas for reducing self-absorption effects

Suppression of satellite emission & higher spectral purity

Long wavelength (low critical density): CO2 laser@1019 /cc

Short laser pulse duration: ~1-2 ns@YAG laser (1064 nm)

Low density targets

Discharge plasmas (low density plasmas)

Low density, high temperature plasma

Nd:YAG & CO2 laser-produced Gd plasmas

3 4 5 6 7 8 9 10 11 120

0.2

0.4

0.6

0.8

1

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

3 4 5 6 7 8 9 10 11 120

0.2

0.4

0.6

0.8

1

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

T. Higashiguchi et al., Optics Express (accepted).

Spectral purity: efficiency in 0.6%BW at 6.x nm

CO2Nd:YAG

1010 1011 1012 10130

0.5

1

1.5

2

2.5

3

Laser intensity (W/cm2)

Spec

tral e

fficie

ncy

(%)

CO2Nd:YAG

1010 1011 1012 10130

0.2

0.4

0.6

0.8

1

Laser intensity (W/cm2)

Conv

ersio

n ef

ficie

ncy

(%)

T. Higashiguchi et al., Optics Express (accepted).

Plasma parameters

T. Higashiguchi et al., Optics Express (accepted).

log n e

(cm

-3)

log n e

(cm

-3)

T e (e

V)

T e (e

V)

(a) (c)

(b) (d)

Nd:YAG CO2

Toward a single shot flash source in WW for Bio Photo in LABOur objective is a demonstration of high-brightness, high energy EUV/soft x-ray source in water window (3.2 nm) for the first time in the world!!!

CO2 Laser

Multilayermirror

Laser

Plasma light source

Soft X-ray CCD

Biological sample

EUV

Pinhole

SchwarzchildOptics

0

50

100

150

200

250

300

350

Inte

nsity

(arb

. uni

ts) ExperimentCalculation

6 6.5 7 7.5 8

Wavelength (nm)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Inte

nsity

(arb

. uni

ts)

EUV & BEUV source study Wavelength: 13.5 & 6.x nm

Lithography Life Innovation Compact source development for Bio.

Wavelength: 2-4 nm

Proposal (APL x 1)

10.1117/2.1201109.003765

Shorter-wavelength extreme-UVsources below 10nmTakeshi Higashiguchi, Takamitsu Otsuka, Noboru Yugami,Weihua Jiang, Akira Endo, Padraig Dunne, Bowen Li, andGerry O’Sullivan

A next-generation laser-produced plasma system based on rare-earthtargets generates strong resonant line emissions at 6.5–6.7nm.

In recent years, laser-produced dense plasmas have been attract-ing attention as high-efficiency, high-power sources of extremeUV (EUV) radiation. Sources with a wavelength less than 10nmare of particular interest for use in next-generation semiconduc-tor lithography and for other applications, such as materials sci-ence and biological imaging. Manufacturer Cymer, for example,has already shipped a high-average-power 13.5nm engineer-ing prototype to a semiconductor device company that wouldenable high-volume production at a power level of 80W.1 Thissource optimizes unresolved transition array (UTA) emission ofhighly ionized tin for high conversion efficiency (CE) of the in-put laser energy to the in-band (i.e., a bandwidth of about 2%around 13.5nm) EUV energy. Full recovery of the injected fuel isrealized through ion deflection in a magnetic field. Low-densitytargets like tin further enable suppression of satellite (i.e., peri-pheral) emission. Full ionization, which helps to control debrisand thus avoid damage to the source mirror, is attained withshort-pulse CO2 laser irradiation.

Recently, the possibility of switching to an even shorterEUV wavelength of 6.Xnm was suggested.2 In fact, 6.Xnmbeyond-EUV (BEUV) emission can be coupled with a molyb-denum/boron carbide (Mo/B4C) or lanthanum/boron carbide(La/B4C) multilayer mirror whose reflectivity is currently 40%at 6.5–6.7nm (theoretical maximum >70%). The UTA emissionexploited in tin is scalable to shorter wavelengths. The rare-earth element gadolinium (Gd) has a CE similar to that of tin,though at a higher plasma temperature, within a narrow spectralrange centered near 6.7nm. However, no fundamental researchhas been reported on spectral behavior at 6.7nm and its depen-dence on various parameters, such as laser wavelength, initialtarget density, and dual-laser-pulse delay. EUV emission at thislevel could be tuned for use with a Mo/B4C multilayer mirrorto power practical sources.

Figure 1. Electron temperature dependence of the gadolinium (Gd) ionpopulation according to the steady-state collisional-radiative model (a).The weighted oscillation strength (gf) spectra of the resonant lines foreach contributing ion stage are shown in (b) and (c).

In a proof-of-principle experiment, we produced a source withpeak emission around 6.5–6.7nm.3, 4 gadolinium and terbium(another rare-earth element) produce strong narrow-band emis-sion, again attributable to thousands of resonance lines that

Continued on next page

In vivo cell observation Original micro source

Single shot, flash biological imaging

Si / SiO

Sn: 10 - 15 um φ

Laser 2

Shorter wavelength

APL x 7 (2010-2012)

CE ~ 5% CE ~ 0.1%, 100 μJ (?)WW 100-μJ at 100-mJ laser

Low temperature result from Bi by 150-ps laser

0

100

200

300

400

500

600

0

0.2

0.4

0.6

0.8

1.0

Inte

nsity

(arb

. uni

ts)

Experimental result700 eV

0

0.04

0.08

0.12

0.16

0.20190 eV(a)

12

3

4

1 2 3 4 5 6

Wavelength (nm)In

tens

ity (a

rb. u

nits

) 1: 4f-5g, < Bi35+

2,3: 4p-4d, 4d-4f, Bi36+-Bi45+ 4: 4d-4f

T. Higashiguchi et al., Appl. Phys. Lett. 100, 014103 (2012).

Laser intensity dependence in Bi emission

1 2 3 4 5 6

Inte

nsity

(arb

. uni

ts)

Wavelength (nm)

9.5 x 1013 W/cm25.4 x 1013 W/cm22.9 x 1013 W/cm2

(a) n=4 - n=4n=4 - n=5

200

300

400

500

600

700

Pho

ton

ener

gy (e

V)

1013 1014

Laser intensity (W/cm2)

(b)600

500

400

300

200

100

0

T. Higashiguchi et al., Appl. Phys. Lett. 100, 014103 (2012).

Concept: Unresolved transition array (UTA) many resonant lines

!λ (nm)

!λ (nm)

2 4

2 4

(a) Line spectrum

(b) UTA

02

46

500

1000

15000

0.01

0.02

0.03

0.04

0.05

Wavelength (nm)Te (eV)

Rel

ativ

e in

tens

ity (a

.u.)

Figure 2: Takeshi Higashiguchi et al.

13.5 nm CE ~ 5% by Sn6.x nm CE ~ 1% by Gd/Tb

3 nm and/or 4 nm CE > 0.1% by Bi

T. Higashiguchi et al., Appl. Phys. Lett. 100, 014103 (2012).

Extreme Condition: keV Bi plasma spectra

Low density, high temperature 1-keV plasma

optical thin, low density optical thick, high densityOct.17 : 30 shots May 27 - May 31 : 49 shots

0 500 1000 15000

0.5

1

Ion

fract

ion

Te (eV)

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

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27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

24+

27+30+ 33+36+

39+42+ 45

+

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T. Higashiguchi et al., Appl. Phys. Lett. 100, 014103 (2012).

15

Figure 5

Lower temperature ~0.2 keV vs 1 keV

J. Phys. B 45, 245004 (2012).Appl. Phys. Lett. 102, 041117 (2013).

Zr Bi

J. Phys. B 45, 245004 (2012).Appl. Phys. Lett. 102, 041117 (2013).

Zr plasma WW source for 1-μm laser

252

Fig. 6 Deˆnition of parameters for ellipsoid (a) and KB mirrors(b).

252 July 2006 Vol.19 No.4

y

Rm Rs 1)

Rm 2/(1/p 1/q)/sin ui (8)

Rs 2 sin ui/(1/p 1/q) Rm sin2 ui (9)

p q

q 1/q 0

X p 15 50 m, q 5 20 m, ui1 10 mrad Rm 0.1 10 km, Rs 30 100 mm

4 6

uiRm Rs

S

F

F S q/p (10)

M q/p

M 0.1 1

4.2 11 1

4 1 km

1 m

Rm 1 km

0.1 mm

km

7

mm

1

4.3 2

Fig. 6(b)

mm

mm

Fig. 6(a)

1 2 2

2

Rm100 m Zeiss

KEK PF

BL9A

2

2 10)

1 2 mm