Yuelin Li , James Dunn , Albert Osterheld

iLSA Institute for Laser Science and Applications 7/21/2000

Free Electron Laser Conference 2000, 13 to 18 August 2000, Durham, North Carolina

Yuelin Li1, James Dunn2, Albert Osterheld2, Joseph Nilsen2, and Vyacheslav N. Shlyaptsev3

1Institute of Laser Science and ApplicationsLawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550

2Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550

3Department of Applied Science University of California at Davis-Livermore, Livermore, CA 94550

Work performed under the auspices of the US Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48

Progress of plasma tableProgress of plasma table--top Xtop X--ray lasers at LLNLray lasers at LLNL



What is a plasma X-ray laser

Pump: laser, particle beams, discharges…

Plasma columns

Population inversion and X-ray lasing: 10-6

Energy loss: incoherent radiation

Energy loss: Hydrodynamicsheat conduction

Plasma lasers are traditional lasers that lase via population inversion on atomic and ionic energy levels



40 50 60 70 80

5

10

15

20

25

Wav

eelg

nth

(nm

)

Z

Ni-like Mo (Z=42) (Mo14+)

3d 1S0

4d 1P1

4f 1P1

4d 1S0

4p 1P1

18.9 nm

22.6 nm

Ground state: 1s2 2s2 2p6 3s2 3p6 3d10

Wavelengths of Ni-like lasers

Y (Z=39)

Sn (Z=50)

Population inversion: Ni-like X-ray lasers



X-ray laser at LLNL: NOVA experiments (1980s-early 1990s)

• Lasing from 3.5 to 33 nm• X-ray laser interferometer/More deflectometory• X-ray laser microscopy/holographyPump energies: ~kJRep Rate: ~hours



The transient collisional excitation scheme

The long pulse prepares a large plasmaThe long pulse prepares a large plasmaThe short pulse generates the high gainThe short pulse generates the high gain• The high gain allows efficient amplification

(saturation) with a short target length • Using the compact CPA lasers

Time

short pulse

long pulse

Nickles et al, Phys Rev Lett 78, 2748 (1997); Dunn et al, Phys Rev Lett 80, 2825 (1998)

Notes: Plasma X-ray laser gain = (FEL gain length)-1

Plasma X-ray laser gain length = ln(FEL gain)





Detailed setup: traveling wave (TWE) and diagnostics

Parabola

EchelonFlat mirror

Laser beam

Cylindricallens

0.0 0.2 0.4 0.6 0.8 1.010-2

10-1

100

101

102

No TWE TWE

XR

L ou

tput

(Arb

. Uni

ts)

∆t (ns)

TWE

Spectrometer+CCD camera

CCD

multilayer mirror

multilayer mirror

multilayer mirror

target

z (m m )

y (m

m)

!99022 3m.im o\!990223 2 .7

-0 .2 -0 .15 -0 .1 -0 .05 0 0 .05

-0 .1

-0 .0 5

0

0 .0 5

0 .1



X-ray laser diagnostics: multilayer imaging system

15 20 25 3010-4

10-3

10-2

10-1

100

Multilayer mirror reflectivity

M3 M1, M2 total

Ref

lect

ivity

Wavelength (nm)

y (m m )

z (m

m)

!99 0428 m.imo\!99 0428 2 .3 ,s q rt(I)

-0 .1 -0 .0 5 0 0 .0 5 0 .1

0

0 .05

0 .1

0 .15

0 .2

0

10

20

30

40

50

60

70

80

90

y (m m )

z (m

m)

!99 0428 m.imo\!99 0428 2 .6 ,s q rt(I)

-0 .1 -0 .0 5 0 0 .0 5 0 .1

0

0 .05

0 .1

0 .15

0 .2

0

10

20

30

40

50

60

70

80

90

Mo: 18.9 nm

Nb: 20.3 nm



Spectra of Pd and Mo

10 mm 9 mmMo (Z=42) Pd (Z=46)

Beam divergence

Wav

elen

gth

On-axis X-ray laser (XRL) spectra

XRL lines

10 15 20 25 30 35

0

1000

2000

3000

4000

20.4 nm

32.6 nm

30.4 nm

14 nm

14.6 nm18.9 nm

13 nm

12 nm

Nb Mo Pd Ag Cd Sn Ti V

Inte

nsity

(Arb

. Uni

ts)

Wavelength (nm)

18.9 nm

14.7 nm



0.0 0.2 0.4 0.6 0.8 1.010-1

101

103

105

4d 1P1-4p 1P1

22.6 nm

9.8 cm-1

GL=9.8

4d 1S0-4p 1P1

18.9 nm

35.6 cm-1

GL=16.6

Out

put (

Arb

. Uni

ts)

Target length (cm)

Saturation of the 18.9 nm Ni-like Mo X-ray laser

15 20 25 30

100

101

102

103

22.6 nm

18.9 nm

Inte

nsity

(Arb

. Uni

ts)

Wavelength (nm)

Spectrum of a 1 cm target A gain length of 16.6 is obtained

Li et al, submitted to Science

Mo



Measurement of the Ni-like Mo 18.9 nm XRL beam divergence

10 mm 9 mm

Pd

XRL divergence

-5 0 5 100

25

50

75

100 Mo

10 mm 7 mm 5 mm

Inte

nsity

(a.u

.)

Angle (mrad)

0.0 0.2 0.4 0.6 0.8 1.0

-5

0

5

10Mo

Near edge Far edge

φ (m

rad)

Target length (cm)



Temporal characterization of Ni-like Mo XRL at 18.9 nm

When no traveling wave is applied, the X-ray experiences the gain as a function the propagation distance, i.e., the traveling time

0 2 4 6 8 1010-1

100

101

102

103

104

7.9 cm-11.7 cm-1

0 cm-1

12.1 cm-1

19.2 cm-1

Inte

nsity

(a. u

.)

Target length (mm)10 15 20 25 30

0

5

10

15

20 Mo

Gpeak~30 cm-1

τgain~15 ps

Gai

n (c

m-1)

Time (ps)

Dunn et al, Opt Lett 24, 101 (1999)



Saturation and temporal characterization of the 14.7 nm Ni-like Pd X-ray laser

A gain length of 21.6 is obtained

Dunn et al, submitted to Phys Rev Lett

5 10 15 20 25

0

10

20

30

40

50

60

70

Pd

Gpeak=139 cm-1

τ=4 ps

Gai

n (c

m-1)

Time (ps)0.2 0.4 0.6 0.8 1.0

100

101

102

103

104 Pd14.7 nm

G=60.4 cm-1

No Traveling wave Traveling wave

Inte

nsity

(CC

D c

ount

s)

Target Length (cm)

A gain life time of ~4 ps is deduced from the non-traveling wave measurement



0 1 2 3 4 5

0

1

2

Long Pulse Energy (J)

0.1 ns 0.4 ns 0.7 ns 1.0 ns

EX

RL (

µJ)

Mo 18.9 nm XRL output energy and intensity

0 1 2 3 4 5

0123456

ISAT

I XR

L (G

W c

m-2)

Long Pulse Energy (J)



0.0

0.2

0.4

0.6

0.8

(a)

EX

RL (

µJ)

0 2 4 6 8 10

012345

(b)

Are

a (1

0-3 m

m2 )

Number of shots

Comparison of near-field images XRL output of a set of non-consecutive shots

EL=1-1.5 J, ES=5 J, ∆t=0.7 ns, targets are 1 cm long.

Stability of the Plasma XRL

y (m m )

z (m

m)

!99 0223m.imo \!9902 230 .6 ,s q rt(I)

-0 .1 -0 .05 0 0 .05 0 .1

0

0 .05

0 .1

0 .15

0 .2

y (m m )

z (m

m)

!99 0223m.imo \!9902 231 .0 ,s q rt(I)

-0 .1 -0 .05 0 0 .05 0 .1-0 .05

0

0 .05

0 .1

0 .15

0 .2

y (m m )

z (m

m)

!99 0223m.imo \!9902 232 .1 ,s q rt(I)

-0 .1 -0 .05 0 0 .05 0 .1

-0 .05

0

0 .05

0 .1

0 .15

0 .2

y (m m )

z (m

m)

!99 0223m.imo \!9902 232 .5 ,s q rt(I)

-0 .1 -0 .05 0 0 .05 0 .1

-0 .05

0

0 .05

0 .1

0 .15

0 .2



Brightness of the Plasama XRL

100 101 102 103 104 1051014

1016

1018

1020

1022

1024

1026

1028

1030

1032

1034

Ne-like Ar XRL

LLNL XRL

Ni-like Ta XRL

Ne-like Y XRL

Ni-like Ag XRLNi-like Sm XRL

Ne-like Ge XRL

APS BM

APS UA

ALS BM

NSLS X1

ALS UND

APS (max)

LCLS

DESY

Bri

ghtn

ess

[pht

ons

s-1 m

m-2 m

rad-2

(0.0

1% B

W)-1

]

Photon energy (eV)100 101 102 103 104 105108

1010

1012

1014

1016

1018

1020

1022

APS (max)

Discharge Table-Top XRL

DESYLCLS

LLNL Table-Top XRL

APS BM

APS UAALS U8.0

SSRL Wiggler

ALS BM

ALS U5.0

NSLS X1

NSLS BM

Bri

ghtn

ess

[pht

ons

s-1 m

m-2 m

rad-2

(0.0

1% B

W)-1

]

Photon energy (eV)

Average BrightnessPeak Brightness



Future work

Cavity mirror

Further reduction of the pump power for high rep rates:

longitudinal pump?Innovation in laser tech?New pumping scheme?

Improvement of the temporal and spatial coherence:

Build a Cavity.

Target

Coupling mirror

Long pulse beam

Short pulse beam

XRL output



Summary of LLNL XRL accomplishments

Demonstration of X-ray lasers at wavelengths from 12 to 33 nm, the first saturatedtable top XRL system at wavelengths below 20 nm, characterization of the XRL output and demonstration of control of the XRL output

This research has laid the foundation of further development of a user facility for application in plasma diagnostics, surface physics, and imaging experiments, as well as a seeding source for X-ray FEL

Plasma XRL will complement the third and the fourth generation light sources with comparable brightness but better compactness.

Summary

Yuelin Li , James Dunn , Albert Osterheld

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