optical properties of plasmas based on an average-atom modeljohnson/publications/aussem.pdf ·...
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Optical Properties of Plasmas Based on an Average-AtomModel
Walter Johnson, Notre Dame University
Claude Guet, CEA/DAM Ile de France
George Bertsch, University of Washington
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Optical Properties of Plasmas Based on an Average-AtomModel
Walter Johnson, Notre Dame University
Claude Guet, CEA/DAM Ile de France
George Bertsch, University of Washington
• Average Atom Model of a Plasma
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Optical Properties of Plasmas Based on an Average-AtomModel
Walter Johnson, Notre Dame University
Claude Guet, CEA/DAM Ile de France
George Bertsch, University of Washington
• Average Atom Model of a Plasma
• Linear Response ⇒ Kubo-Greenwood formula for σ(ω)
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Optical Properties of Plasmas Based on an Average-AtomModel
Walter Johnson, Notre Dame University
Claude Guet, CEA/DAM Ile de France
George Bertsch, University of Washington
• Average Atom Model of a Plasma
• Linear Response ⇒ Kubo-Greenwood formula for σ(ω)
• Kramers-Kronig Dispersion Relation ⇒ Dielectric Function ε(ω)
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Optical Properties of Plasmas Based on an Average-AtomModel
Walter Johnson, Notre Dame University
Claude Guet, CEA/DAM Ile de France
George Bertsch, University of Washington
• Average Atom Model of a Plasma
• Linear Response ⇒ Kubo-Greenwood formula for σ(ω)
• Kramers-Kronig Dispersion Relation ⇒ Dielectric Function ε(ω)
• Index of refraction n(ω) + iκ(ω) =√ε(ω)
Seminar: UNSW Mar. 30, 2005
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2
Motivation
Free electron formula for index of refraction is used to determine electron densities.
n =
√1− ω
20
ω2≈ 1− ω2
0
2ω2< 1 where ω2
0 = 4πe2
m
Nfree
Ω
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2
Motivation
Free electron formula for index of refraction is used to determine electron densities.
n =
√1− ω
20
ω2≈ 1− ω2
0
2ω2< 1 where ω2
0 = 4πe2
m
Nfree
Ω
Problem: Recent experiments on Al plasmas find n > 1 at few eV temperatures
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2
Motivation
Free electron formula for index of refraction is used to determine electron densities.
n =
√1− ω
20
ω2≈ 1− ω2
0
2ω2< 1 where ω2
0 = 4πe2
m
Nfree
Ω
Problem: Recent experiments on Al plasmas find n > 1 at few eV temperatures
Reason: Effect of bound electrons on optical properties.
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2
Motivation
Free electron formula for index of refraction is used to determine electron densities.
n =
√1− ω
20
ω2≈ 1− ω2
0
2ω2< 1 where ω2
0 = 4πe2
m
Nfree
Ω
Problem: Recent experiments on Al plasmas find n > 1 at few eV temperatures
Reason: Effect of bound electrons on optical properties.
• LLNL comet laser facility1 (14.7 nm Ni-like Pd laser)
• Advanced Photon Research Center JAERI2 (13.9 nm Ni-like Ag laser)
1J. Filevich et al. Proceedings of the 9th International Conference on X-Ray Lasers, May 23-28 (2004)2H. Tang et al., Appl. Phys. B78, 975 (2004)
Seminar: UNSW Mar. 30, 2005
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3
TANG et al. Diagnostics of laser-induced plasma with soft X-ray (13.9 nm) bi-mirror interference microscopy 977
FIGURE 2 a Interference fringes after removing self-emission of the Al plasma. The fringes evolve with the increasing of diagnosing delay (0 ∼ 5 ns). Onlythe fringes very close to the target surface cannot be resolved due to the over intense self-emission. b Interference fringe pattern c Electron density map forthe 1 ns-delay and for an irradiance of 1.4×1011 Wcm−2
a 2p-3d transition of Al2+ ions, the wavelength of which be-ing 13.883 nm [11]. This wavelength is very close to the X-raylaser one (13.887 nm) [12]. At 2 ∼ 3 nanoseconds after theheating pulse, the plasma temperature falls-off and the highlyionized plasma starts to recombine, leading to a reduced freeelectron density and a larger Al2+ ion density, which bothincrease the refractive index. Another possible mechanism in-volves the contribution of bound-free transitions in neutralatoms to the refraction index. Al2+ ions and neutral atomsexist at this period of plasma development. Their effect onthe refractive index, which can be neglected in the highlyionized, laser-heated plasma, should be considered in therecombining plasma. Otherwise, estimation of the electrondensity from the fringe shift may be underestimated. More de-tailed quantitative investigation of the effect of the Al2+ ionswill be performed by hydrodynamic simulation in our futurework.
3 Summary
We present the results of an X-ray interference mi-croscopy of a dense laser-induced plasma using a wavefrontdivision bi-mirror interferometer and a transient picosecondNi-like Ag X-ray laser (wavelength ∼ 13.9 nm). Interferencemicroscopy pattern of the Al (Z = 13) plasma have beenrecorded successfully. Electron densities are measured fromthe interference fringe shifts under the pumping intensity of∼ 1011 Wcm−2. For the aluminum plasma diagnosed 2 and 3nanoseconds after the heating pulse, opposite fringe shifts areobserved. Two possible explanations for this behavior are dis-
cussed. These results will contribute to the validation of the1D and 2D hydrodynamic codes and a better understanding ofthe physics of laser-produced plasma.
REFERENCES
1 D.T. Attwood, D.W. Sweeney, J.M. Auerbach, P.H.Y. Lee: Phys. Rev.Lett. 40, 184 (1978)
2 P.E. Young, P.R. Bolton: Phys. Rev. Lett. 77, 4556 (1996); P.E. Young,C.H. Still, D.E. Hinkel, W.L. Kruer, E.A. Williams, R.L. Berger,K.G. Estabrook: Phys. Rev. Lett. 81, 1425 (1998)
3 L.B. Da Silva, T.W. Barbee, Jr., R. Cauble, P. Celliers, D. Ciarlo,S. Libby, R.A. London, D. Matthews, S. Mrowka, J.C. Moreno, D. Ress,J.E. Trebes, A.S. Wan, F. Weber: Phys. Rev. Lett. 74, 3991 (1995)
4 J.J. Rocca, C.H. Moreno, M.C. Marconi, K. Kanizay: Opt. Lett. 24, 420(1999)
5 J. Filevich, K. Kanizay, M.C. Marconi, J.L.A. Chilla, J.J. Rocca: Opt.Lett. 25, 356 (2000)
6 A. Klisnick, J. Kuba, D. Ros, R. Smith, G. Jamelot, C. Chenais-Popovics, R. Keenan, S.J. Topping, C.L.S. Lewis, F. Strati, G.J. Tallents,D. Neely, R. Clarke, J. Collier, A.G. Macphee, F. Bortolotto, P.V. Nick-les, K.A. Janulewicz: Phys. Rev. A 65, 033 810 (2002)
7 T. Kawachi, M. Kado, M. Tanaka, A. Sasaki, N. Hasegawa, A. Kil-pio, S. Namba, K. Nagashima, P. Lu, K. Takahashi, H. Tang, R. Tai,M. Kishimoto, M. Koike, H. Daido, Y. Kato: Phys. Rev. A 66, 033 815(2002)
8 R.F. Smith, J. Dunn, J Nilsen, V.N. Shlyaptsev, S. Moon, J. Filevich,J.J. Rocca, M.C. Marconi, J.R. Hunter, T.W. Barbee: Phys. Rev. Lett. 89,065 004 (2002)
9 D. Joyeux, R. Mercier, D. Phalippou, M. Mullot, M. Lamare: J. Phys. IVFrance 11, Pr2, 511 (2001)
10 R. Mercier, M. Mullot, M. Lamare, G. Tissot: SPIE Proc. 3739, 155(1999)
11 NIST Atomic Spectra Database(http://physics.nist.gov/cgi-bin/AtData/main_asd)
12 D. Ros: Thèse de l’Universite Paris-Sud XI, Orsay (1998) (in French)
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4
Average-Atom Model
QM version of a model proposed by Feynman, Metropolis, and Teller3
Inside a neutral Wigner-Seitz cell: Ω = A/(Avagadro No.× density)[p2
2m− Zr
+ V
]ψi(r) = εiψi(r) (1)
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4
Average-Atom Model
QM version of a model proposed by Feynman, Metropolis, and Teller3
Inside a neutral Wigner-Seitz cell: Ω = A/(Avagadro No.× density)[p2
2m− Zr
+ V
]ψi(r) = εiψi(r) (1)
V = Vdir(r) + Vexc(r) for r ≤ R and V = 0 otherwise.
∇2Vdir = −4πρ (2)
Vexc(ρ) is given in the local density approximation
3R. P. Feynman, N. Metropolis and E. Teller, Phys. Rev. 75 1561 (1949)
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5
Thermal Average Electron Density
Contributions to the density are
ρb(r) =1
4πr2
∑l
2(2l + 1)∑n
f(εnl)Pnl(r)2
(3)
ρc(r) =1
4πr2
∑l
2(2l + 1)
∫ ∞0
dε f(ε)Pεl(r)2
(4)
where
f(ε) =1
1 + exp[(ε− µ)/kT ]
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5
Thermal Average Electron Density
Contributions to the density are
ρb(r) =1
4πr2
∑l
2(2l + 1)∑n
f(εnl)Pnl(r)2
(3)
ρc(r) =1
4πr2
∑l
2(2l + 1)
∫ ∞0
dε f(ε)Pεl(r)2
(4)
where
f(ε) =1
1 + exp[(ε− µ)/kT ]
The chemical potential µ is chosen to insure electric neutrality:
Z =
∫r<R
ρ(r) d3r ≡
∫ R
0
4πr2ρ(r) dr . (5)
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5
Thermal Average Electron Density
Contributions to the density are
ρb(r) =1
4πr2
∑l
2(2l + 1)∑n
f(εnl)Pnl(r)2
(3)
ρc(r) =1
4πr2
∑l
2(2l + 1)
∫ ∞0
dε f(ε)Pεl(r)2
(4)
where
f(ε) =1
1 + exp[(ε− µ)/kT ]
The chemical potential µ is chosen to insure electric neutrality:
Z =
∫r<R
ρ(r) d3r ≡
∫ R
0
4πr2ρ(r) dr . (5)
Eqs. (1-5) are solved self-consistently for ρ, V , and µ.
Seminar: UNSW Mar. 30, 2005
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6
Example
Al: density 0.27 gm/cc, T = 5 eV, R = 6.44 a.u., µ = −0.3823 a.u.
Bound States Continuum States
State Energy n(l) l n(l) n0(l) ∆n(l)
1s -55.189 2.0000 0 0.1090 0.1975 -0.0885
2s -3.980 2.0000 1 0.2149 0.3513 -0.1364
2p -2.610 6.0000 2 0.6031 0.3192 0.2839
3s -0.259 0.6759 3 0.2892 0.2232 0.0660
3p -0.054 0.8300 4 0.1514 0.1313 0.0201
5 0.0735 0.0674 0.0061
6 0.0326 0.0308 0.0018
7 0.0132 0.0127 0.0005
8 0.0049 0.0048 0.0001
9 0.0017 0.0016 0.0001
10 0.0005 0.0005 0.0000
Nbound 11.5059 Nfree 1.4941 1.3404 0.1537
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7
0 2 4 6 8
10-3
10-2
10-1
ρc(r)ρ0
0 2 4 6 8r (a.u.)
0
5
10
15
4πr2ρb(r)
4πr2ρc(r)Zeff(r)
RWS
RWS
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8
Pressure
P =13
[Txx + Tyy + Tzz]∣∣∣r=R
≈ (2mkT )5/2
6mπ2 I3/2(µ/kT ),
where Ik(x) is a “Fermi-Dirac” integral
Ik(x) =∫ ∞
0
ykdy
1 + e(y−x)
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8
Pressure
P =13
[Txx + Tyy + Tzz]∣∣∣r=R
≈ (2mkT )5/2
6mπ2 I3/2(µ/kT ),
where Ik(x) is a “Fermi-Dirac” integral
Ik(x) =∫ ∞
0
ykdy
1 + e(y−x)
P = P (Ω, T ) provides an equation of state for the plasma
n.b. atomic unit of [P ]: 294.21 Mbar.
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9
Kinetic and Potential Energies
Ekin =∫d3r
∑i
〈ψi|p2
2m|ψi〉f(εi)
=32P Ω− 1
2Epot
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9
Kinetic and Potential Energies
Ekin =∫d3r
∑i
〈ψi|p2
2m|ψi〉f(εi)
=32P Ω− 1
2Epot
This is the generalized virial theorem.
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10
Entropy
The entropy S of a collection of fermions is given by the expression
TS = −kT∑i
f(εi) ln f(εi) + [1− f(εi)] ln [1− f(εi)]
where f(εi) = 1/ [1 + exp (εi − µ)/kT ]
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10
Entropy
The entropy S of a collection of fermions is given by the expression
TS = −kT∑i
f(εi) ln f(εi) + [1− f(εi)] ln [1− f(εi)]
where f(εi) = 1/ [1 + exp (εi − µ)/kT ] This can be manipulated to give
TS =53Ekin + Ee−n + 2Ee−e − µN
=52P Ω +
16Ee−n +
76Ee−e − µN
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11
Other Thermodynamic Quantities
The internal energy U and the Helmholtz free energy F are given by
U = Ekin + Epot =3
2P Ω +
1
2Ee−n +
1
2Ee−e
F = U − TS = −P Ω +1
3Ee−n −
2
3Ee−e +Nµ
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11
Other Thermodynamic Quantities
The internal energy U and the Helmholtz free energy F are given by
U = Ekin + Epot =3
2P Ω +
1
2Ee−n +
1
2Ee−e
F = U − TS = −P Ω +1
3Ee−n −
2
3Ee−e +Nµ
From thermodynamics, we know that
dU = dQ− PdΩ = TdS − PdΩ
dF = −SdT − PdΩ
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11
Other Thermodynamic Quantities
The internal energy U and the Helmholtz free energy F are given by
U = Ekin + Epot =3
2P Ω +
1
2Ee−n +
1
2Ee−e
F = U − TS = −P Ω +1
3Ee−n −
2
3Ee−e +Nµ
From thermodynamics, we know that
dU = dQ− PdΩ = TdS − PdΩ
dF = −SdT − PdΩ
The Helmholtz free energy is a thermodynamic function of the “natural” variables of the problem,
Ω and T :
S = −∂F
∂T
∣∣∣∣Ω
P = −∂F
∂Ω
∣∣∣∣T
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12
Application: Plasma Conductivity
The Ziman formula4 for the static conductivity of a many-particle system is
σ = −2e2
3
∫d3p
(2π)3v
2τ(p)
∂f
∂E,
where τ(p) is the mean collision time and where f(E) is the Fermi function.
τ(p) =Λ(p)
vΛ(p) =
Ω
σtr(p)
σtr(p) =4π
p2
∞∑l=0
(l + 1) sin2
(δl+1 − δl) τ(p) =Ω
v σtr(p)
σ = −Ω
3π2
∫ ∞0
dE
[v2
σtr(p)
]∂f
∂E.
4G. D. Mahan, Many-Particle Physics, Plenum, 2000
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13
Phase Shifts
0 1 2 3 4 5Electron Momentum (a.u.)
-3
-2
-1
0
1
2
Phas
e Sh
ift (
rad)
l=0l=1l=2l=3l=4
T = 10 eV and metallic density
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14
Resistivity of Aluminum
0 20 40 60 80 100T (eV)
0
50
100
150
200
250
Res
istiv
ity (µ
Ω−c
m)
Ziman FormulaMilchberg et al. (1988)
Metallic density
Seminar: UNSW Mar. 30, 2005
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15
Linear Response and the Kubo-Greenwood Formula
Apply an electric field to the average atom:
E(t) = F z sinωt A(t) =F
ωz cosωt
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15
Linear Response and the Kubo-Greenwood Formula
Apply an electric field to the average atom:
E(t) = F z sinωt A(t) =F
ωz cosωt
The time dependent Schrodinger equation becomes[T0 + V (n, r)− eF
ωvz cosωt
]ψi(r, t) = i
∂
∂tψi(r, t)
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15
Linear Response and the Kubo-Greenwood Formula
Apply an electric field to the average atom:
E(t) = F z sinωt A(t) =F
ωz cosωt
The time dependent Schrodinger equation becomes[T0 + V (n, r)− eF
ωvz cosωt
]ψi(r, t) = i
∂
∂tψi(r, t)
The current density is
Jz(t) =2eΩ
∑i
fi 〈ψi(t)|vz|ψi(t)〉
Seminar: UNSW Mar. 30, 2005
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16
Solution Ansatz
ψi(r, t) = ui(r)e−iεit + w+i (r)e−i(εi+ω)t + w−i (r)e−i(εi−ω)t
[T0 + V (n, r)]ui(r) = εiui(r)
[T0 + V (n, r)− (εi ± ω)]w±i (r) =eF
2ωvz ui(r)
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16
Solution Ansatz
ψi(r, t) = ui(r)e−iεit + w+i (r)e−i(εi+ω)t + w−i (r)e−i(εi−ω)t
[T0 + V (n, r)]ui(r) = εiui(r)
[T0 + V (n, r)− (εi ± ω)]w±i (r) =eF
2ωvz ui(r)
The current density becomes
Jz(t) =2eΩ
∑i
fi 〈ψi(t)|vz|ψi(t)〉
=2eΩ
∑i
fi[(〈ui|vz|w+
i 〉+ 〈w−i |vz|ui〉)e−iωt + c.c.
]
Seminar: UNSW Mar. 30, 2005
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17
Eigenvalue Expansion
w+i (r) =
∑j
Xji uj(r) w−i (r) =
∑j
Y ji uj(r)
Xji =
eF
2ω〈j|vz|i〉
εj − iη − εi − ωY ji =
eF
2ω〈j|vz|i〉
εj − iη − εi + ω
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17
Eigenvalue Expansion
w+i (r) =
∑j
Xji uj(r) w−i (r) =
∑j
Y ji uj(r)
Xji =
eF
2ω〈j|vz|i〉
εj − iη − εi − ωY ji =
eF
2ω〈j|vz|i〉
εj − iη − εi + ω
The response current may be written
J =4eΩ
∑ij
fi
[<(〈i|vz|j〉Xj
i + 〈j|vz|i〉Y j?i)
cosωt
+ =(〈i|vz|j〉Xj
i + 〈j|vz|i〉Y j?i)
sinωt]
Seminar: UNSW Mar. 30, 2005
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18
Kubo-Greenwood
• Linearize ψi(r, t) in F
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18
Kubo-Greenwood
• Linearize ψi(r, t) in F
• Evaluate the response current: J = Jin sin(ωt) + Jout cos(ωt)
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18
Kubo-Greenwood
• Linearize ψi(r, t) in F
• Evaluate the response current: J = Jin sin(ωt) + Jout cos(ωt)
• Determine σ(ω): Jin(t) = σ(ω)Ez(t)
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18
Kubo-Greenwood
• Linearize ψi(r, t) in F
• Evaluate the response current: J = Jin sin(ωt) + Jout cos(ωt)
• Determine σ(ω): Jin(t) = σ(ω)Ez(t)
Result:
σ(ω) =2πe2
ωΩ
∑ij
(fi − fj) |〈j|vz|i〉|2 δ(εj − εi − ω),
which is an average-atom version of the Kubo5-Greenwood6 formula.
5 R. Kubo, J. Phys. Soc. Jpn. 12, 570 (1957)6D. A. Greenwood, Proc. Phys. Soc. London 715, 585 (1958)
Seminar: UNSW Mar. 30, 2005
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19
Free-Free Contribution to Conductivity
0.01 0.1 1Photon Energy (a.u.)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
σ ff(ω
) (a
.u.)
T=5eVρ=0.27 gm/cc
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19
Free-Free Contribution to Conductivity
0.01 0.1 1Photon Energy (a.u.)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
σ ff(ω
) (a
.u.)
T=5eVρ=0.27 gm/cc
Michael Kuchiev has prepared an elegant note on the low-frequency conductivity
explaining the origin of the infrared divergence and proposing a remedy.
Seminar: UNSW Mar. 30, 2005
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20
Bound-Bound Contribution to Conductivity
0.01 0.1 1 10Photon Energy (a.u.)
0
0.001
0.002
0.003
0.004
σ bb(ω
) (a.
u.)
3s-3p
2p-3s 2s-3p
T=3eVρ=0.27 gm/cc
Seminar: UNSW Mar. 30, 2005
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21
Bound-Free Contribution to Conductivity
0.01 0.1 1 10Photon Energy (a.u.)
0
0.001
0.002
0.003
0.004
0.005
σ bf(ω
) (a.
u.)
3-ε
2-ε
T=3eVρ=0.27 gm/cc
Seminar: UNSW Mar. 30, 2005
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22
Optical Properties
For a conducting medium, the dielectric function is related to the complexconductivity by
ε(ω) = 1 + 4πiσ(ω)ω
We know <σ(ω); we must evaluate =σ(ω)
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22
Optical Properties
For a conducting medium, the dielectric function is related to the complexconductivity by
ε(ω) = 1 + 4πiσ(ω)ω
We know <σ(ω); we must evaluate =σ(ω)
From analytic properties of σ(ω) one infers the dispersion relation7
=σ(ω0) =2ω0
π−∫ ∞
0
<σ(ω)ω2
0 − ω2dω.
7R. de L. Kronig and H. A. Kramers, Atti Congr. Intern. Fisici, 2, 545 (1927)
Seminar: UNSW Mar. 30, 2005
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23
Application of Dispersion Relation
0.001 0.01 0.1 1Photon Energy (a.u.)
-0.030
-0.020
-0.010
0.000
0.010
0.020
0.030
Con
duct
ivity
(a.u
.)
Re[σ(ω)]Im[σ(ω)]
1 2 3 4Photon Energy (a.u.)
-0.003
-0.002
-0.001
0.000
0.001
0.002
0.003
T=5eVρ=0.27 gm/cc
Seminar: UNSW Mar. 30, 2005
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24
Index of Refraction
<ε(ω) = 1− 4π=σ(ω)ω
=ε(ω) = 4π<σ(ω)ω
,
n+ iκ =√ε.
0.01 0.1 1Photon Energy (a.u.)
10-3
10-2
10-1
100
101
n(ω
) & κ
(ω) n
nfreeκκfree
T=5eVρ=0.27gm/cc
Seminar: UNSW Mar. 30, 2005
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25
Al: Comparison with Free Electron Model
Plasma with ion density nion = 1020/cc
0 20 40 60 80 100Photon Energy (eV)
-10
-5
0
5
10(n
-1)/
(nfr
ee-1
) 2p-4d2p-3d
T=3eV<Z>=1.38
Pd x
-ray
2p-3s Ag
x-ra
ySeminar: UNSW Mar. 30, 2005
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26
Al: Penetration Depth
Plasma with ion density nion = 1020/cc
0 20 40 60 80 100Photon Energy (a.u.)
100
101
102
103
Pene
trat
ion
Dep
th (
µm)
T=3eV<Z>=1.38
Seminar: UNSW Mar. 30, 2005
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27
Conclusions
• Average atom model is a simple way to understand the electronic structure of aplasma. (next step - look at neighbors)
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27
Conclusions
• Average atom model is a simple way to understand the electronic structure of aplasma. (next step - look at neighbors)
• Linear response theory applied to the average atom model. provides a straight-forward method for obtaining the frequency-dependent conductivity.
![Page 53: Optical Properties of Plasmas Based on an Average-Atom Modeljohnson/Publications/aussem.pdf · Optical Properties of Plasmas Based on an Average-Atom Model Walter Johnson, Notre Dame](https://reader030.vdocuments.site/reader030/viewer/2022040820/5e690224e22b8e644b6aa9d3/html5/thumbnails/53.jpg)
27
Conclusions
• Average atom model is a simple way to understand the electronic structure of aplasma. (next step - look at neighbors)
• Linear response theory applied to the average atom model. provides a straight-forward method for obtaining the frequency-dependent conductivity.
• The dielectric function (and index of refraction) can be reconstructed with theaid of a dispersion relation.
![Page 54: Optical Properties of Plasmas Based on an Average-Atom Modeljohnson/Publications/aussem.pdf · Optical Properties of Plasmas Based on an Average-Atom Model Walter Johnson, Notre Dame](https://reader030.vdocuments.site/reader030/viewer/2022040820/5e690224e22b8e644b6aa9d3/html5/thumbnails/54.jpg)
27
Conclusions
• Average atom model is a simple way to understand the electronic structure of aplasma. (next step - look at neighbors)
• Linear response theory applied to the average atom model. provides a straight-forward method for obtaining the frequency-dependent conductivity.
• The dielectric function (and index of refraction) can be reconstructed with theaid of a dispersion relation.
• The model explains “anomalous behavior” of low temperature Al plasmas in the80-90 eV frequency range.
![Page 55: Optical Properties of Plasmas Based on an Average-Atom Modeljohnson/Publications/aussem.pdf · Optical Properties of Plasmas Based on an Average-Atom Model Walter Johnson, Notre Dame](https://reader030.vdocuments.site/reader030/viewer/2022040820/5e690224e22b8e644b6aa9d3/html5/thumbnails/55.jpg)
27
Conclusions
• Average atom model is a simple way to understand the electronic structure of aplasma. (next step - look at neighbors)
• Linear response theory applied to the average atom model. provides a straight-forward method for obtaining the frequency-dependent conductivity.
• The dielectric function (and index of refraction) can be reconstructed with theaid of a dispersion relation.
• The model explains “anomalous behavior” of low temperature Al plasmas in the80-90 eV frequency range.
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Seminar: UNSW Mar. 30, 2005