Orestes vs Electra: Implications of Oscillator Data for KrF Kinetics Modeling*

NRLRadiation Hydrodynamics

Branch

Laser Physics Branch

John L. Giuliani,Paul Kepple, Robert Lehmberg,Matt Myers,and J. Sethian Naval Research Laboratory, Plasma Physics Division

Matt Wolford, Science Applications International, Inc.

Frank Hegeler, Commonwealth Technology, Inc.

George Petrov, Berkeley Research Scholars, Inc.

High Average Power Laser Workshop Albuquerque, N.M. April 9-10, 2003

*Supported by Defense Programs, DOE

Abstract

In recent months the Electra laser has been operated as anoscillator. We will examine some of the experimental datarelevant to KrF kinetics and compare with results from theKrF laser simulation code Orestes. After an introduction to thelaser configuration and the code, four issues will be addressed:

a) laser yield in the Ar/Kr pressure plane, b) 3-body rate depnendence on gas temperature, c) small signal gain, d) yield variation with F2 concentration.

In general, the trend of the data is consistent with the predictionsfrom the Orestes code. However, the data indicates a peaklaser yield at lower F2 abundance than Orestes. This isbeneficial for segmented designs of large amplifiers, butpresents difficulties for the modeling.

Overview: Electra oscillator & Orestes model

outputcouplerRoc=8%

calorimeterrear mirrorRm=98.5%

window transmissionTw=65% - 80%

laser cell

e-beam pump length 95 cm

135 cm

Electra oscillator configuration

Ar/ Kr/ F2

30 cm x 30 cmaperture

14

B. Overview of Orestes Code: Laser physics simulation model.

Physics:

e-beam: ionization and excitationfrom Boltzmann analysis

plasma: 1D axially resolved, separateelectron and gas temperatures

kinetics: 24 species, 122 reactions,Includes KrF vibrational structure

lasing and ASE: 3D, discrete ordinates, time dependent, ASE gain narrowing

Objectives:

system scaling, pulse shaping, improve efficiency

Accomplishments:

validated codedesign analysis for Electra

.

Ar*

Kr*

KrF*(Bv,Cv)

Kr+

ArF*

Kr2F*

Neutral Channel

Ar+

Ion Channel

harpoon ion-ion rec

ArKrF*

absorption α = σ 2F n 2F + σ -F n -F + σ 2KrF n 2KrF + σ 2ArF n 2ArF ...

, gain go

γ, Ar,Kr,F2,F,e-

, , 2Kr Ar F

Kr2F F- Kr

F-Kr

2Kr2Ar

e-

, ,Kr Ar F

24 species122 reactions

-e beam-e beam

γ, F2,e-γ, Ar,Kr,F2,e-

2F

Multi-species plasma chemistry for KrF kinetics

Pbeam=1.3 MW/ cc

no ASE

Pbeam=1.3 MW/ cc

no ASE

1.3 MW/ ccw/ ASE

Pbeam=1730 kW/cc

P(beam) (kW/cc)

1.1 - 1.2 atm20 - 35% Kr0.4 - 0.5% F2

no ASE

out

inI =52.5 kW/cm2

E(laser) (kJ)

McGeoch, et al.,Fusion Tech., 32 , p.610 (1997)

(a) Keio Univ.'s single pass amp

(b) NRL's NIKE double pass amp

Suda, et al.,Appl. Phys. Lett., 51 , p.218 (1987)

1 atm / 99.4% Kr / 0.6% F2

1 atm / 10% Kr / 0.4% F2

I (MW/cm2)in

I - I (MW/cm )out in2

Orestes

Iin (W/ cm 2 )

0.62 MW/ccno ASE

(c) Lebedev's Garpun single pass amp

Iout (W/ cm 2 )

1.15 and 1.75 atm6% Kr0.2% F2

Zvorykin, et al.,Final Report, (2002)

Comparison of ORESTES simulations withexisting data on laser yields.

NRL

Radiation Hydrodynamics

Laser Physics

ORESTES 11/02

a) Laser yield vs Ar/Kr pressure.

Using many runs of the Orestes code, one can constructcontours of laser output (yield) over the Ar/Kr pressure plane.These contours assume a fixed e-beam power depositionprofile Pbeam(t) and F2 concentration.

The model results indicate the existence of a "sweet spot"at ~1 atm adn ~40% Kr. Electra data were obtained alongthree lines of constant composition (40%, 60%, ~100% Kr)vs pressure.

The low yields at high pressure are due to the 3-bodydissociative recombination of KrF: KrF + Kr/Ar +M --> Kr2F/ArKrF + M.The model predicts increasing yield as the pressure is reducedto ~1 atm, but the yield data falls at low pressure becausethe e-beam is not fully stopped in the laser cell and the assumedPbeam is too large.

.

pKr (Torr)

ELECTRARosc = 10%Pbeam = 800 kW/ccT(t=0) = 293 KF2 = 0.5%Tw = 96%30x30x100 cc

100%Kr

60% Ar

40% Kr

ORESTES predicted laser yieldvs pressure and composition for ELECTRA oscillator.

NRLRadiation Hydrodynamics

Laser Physics

ORESTES 09/02

.

Kr/F2=39.7% / 0.3%

initial gas pressure in laser cell

Kr/F2=59.7% / 0.3%Kr/F2=99.7% / 0.3%

Laser energy yield from Electraas an oscillator vs initial gas pressureand Ar/Kr composition.

.

Kr/F2=39.7% / 0.3%

initial gas pressure in laser cell

Kr/F2=59.7% / 0.3%Kr/F2=99.7% / 0.3%

Minumum e-beam energy depositionfrom pressure jump method.

b) 3-body kinetic rates and Tg.

The burst (10 @ 1 Hz) data for yield on Electra can be usedexamine the gas temperature dependence of 3-bodyKrF relaxation reactions, such as,

KrF + Kr + M --> Kr2F + M with rate k ~ Tgα.

Such destruction processes are responsible for the falloff ( )in laser yield seen in the yield contours section a and enhance laser light absorption by Kr2 .F

Results of data and modeling indicate are definitive ,proof that the rates are weakly dependent on gas temperature

.contrary to early theoretical work on reaction kinetics

.

initial gas temperature (K)

α= -0.5

α= -2.5

time

The burst data on Electra addresses a kinetics - .issue on the Tg dependence of three body relation

:Electra osciallator shots10 1@ Hz

1) - Three body relaxation of KrF with Kr is among the most important destruction processes for Kr , F and the product is a strong absorber of 248 .nm laser light

+ + --> KrF Kr M Kr2 + F M @ Tgα

2) Theoretical calculation of this rate indicate a , strong falloff with gas temperatureα = -2.0 -3.0.to ( , . . ., 34, .50, 1977)Shui Appl Phys Lett p

3) Orestes simulations atα= -2.5 indicate that the 2 laser yield should increase by a factor of from the first to the last shot due to the rise in Tg. The burst data on Electra imply a much weaker 3- ,dependence of the body relaxation rate on Tg .as was normally used in Orestes

4) , On the other hand the relative consistency of the data indicates that the lasing medium ,is not adversely afected by the temperature rise .either

c) small signal gain

Two techniques were used to measure the netsmall signal gain (go) of the Electra oscillator:

i) probe laser ii) ASE

The results are shown below together with data fromother experiments. The results from the laser probemethod are consistent with other measurements,but the ASE technique indicates a small value for go.

.mirror

photodiode

laser cell mirror(reflectivity RM)

KrFlasercell

window(transmission Tw)

aperature(1.5 cm φ )

823 cm

aperature(1.5 cmφ )

:Notes ) a no output coupler ) b signal from ASE ) ~1 c mrad openning angle d) single pass (no mirror) = ISP

double pass (w/ mirror) = IDP

ASE measurement of small signal gain on Electra: geometry

Small Signal Gain Measurement(February 26, 2003)

L = 95 cm

L =20 cm L =20 cm

0.91” dia.

PD1 2 in. Cal

305i IiI0

Tw=.64 Tw=.64

Experimental Results (2in. Cal):Input 3.5 mV Output 940 mVInput 1.08 mV Output 850 mVLower Input Output 640 mVNo Input Output 640 mV

Small Signal Gain Results

Iout/Iin=e^(gl)

Assumption 4: The intensity stays below the saturation intensity!! Case 1: 4.7%/cm Iin ~47 kW/cm^2 Iout ~4.1 MW/cm^2Case 2: 5.5 %/cm Iin ~16 kW/cm^2 Iout ~3.1 MW/cm^2If saturation intensity ~1.5 MW/cm^2 then Assumption 4 invalid

Full Rigrod Analysis needed

Helpful Comparison to GarpunDifferences 100 cm E-beam Garpun used 95 cm E-beam ElectraWith Garpun graph Electra small signal gain greater than 7%/cm

0.5

1

5

10

2

20

0.05 0.1 0.5 1 20.2

ASE

laser probe

D.E. Klimek, J.C. Hsia, J.H. Jacob, D.W. Trainor, C. Duzy, and H.A. Hyman, "Kineticsissues for short-pulse KrF laser operation", IEEE J. of Quantum Electronics , Vol.QE-17, pp.1847-1855 (1981). B. Edwards, F. O’Neill, and M.J. Shaw, "Absorption and gain measurements in the KrF lasermedium at high pump rate", Appl. Phys. Lett., 38, pp.843-845 (1981). E.T. Salesky and W.D. Kimura, "Gain and absorption measurements of electron beampumped, high Kr concentration gas mixtures", Appl. Phys. Lett., Vol. 46, pp.927-929 (1985). A. Suda, H. Kumagai, and M. Obara, "Characteristics of an electron beam pumped KrF laseramplifier with an atmospheric-pressure Kr-rich mixture in a strongly saturated region", Appl. Phys.Lett., 51, pp.218-220 (1987). V. Zvorykin, Scientific Report March 2001-March 2002, (2002). Electra measurements (03/2003)

Small signal net gain from Electraand other KrF lasers.

. .

near peak output intensity (140 ns)

Tw=90%

80%

70%

60%

ORESTES 11/02

F2 abundance (%) F2 abundance (%)

8% output coupler98.5% mirror reflection

Isat hνσseτ

=

go

Isat α

Ilaser

d) F2 dependence

A scan of the laser yield with the F2 concentrationwas performed at fixed Ar and total pressures and the yieldwas observed to peak at 0.25% F2. This is contrary toOrestes modeling which indicates a peak at the largerconcentration of 0.4%. A low e-beam deposition wouldshift the calculated peak to lower F2, but the observedyields and energy deposition of section (c) rule thisout.

Adjustment of rates is under study to match theobserved peak at low F2 concentration. Relevant reactionsinclude

F2 + e- --> F- + F and Ar2+/Kr2+ + e- --> 2Ar/2Kr

20 psiAr=60%Kr=40-0.X%F2=0.X %

= Electra data

Electra oscillator yields as afunction of F2 anundance

Orest es04/ 03

Tw

=76%, Eb=9.0 kJ

Tw

=80%, Eb=8.6 kJ, no Kr**+M->Kr*+M

= Electra data

Tw

=63%, Eb=8.6 kJ, F+e-+F2->F-+F2 @10-24

Tw

=100%, Eb=4.3 kJ

Time Response of Oscillator at Various Fluorine Concentrations

-100 0 100 200 300 400Time (ns)

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

Intensity (arb.)

0.1%F2, 39.9% Kr, 60% Ar

0.7%F2

39.3% Kr60% Ar

0.25%F2, 39.75% Kr, 60% Ar

runname=Electra oscillator chemset= kan1 quadset= RL_6 NFGRP= 4 NP NL NI NJ NK NS NR MP XAMP YAMP ZAMP ZPMP AR% KR% F2% atm T0

12 12 3 3 12 62 123 8 30.0 30.0 120.0 100.0 59.800 40.000 0.200 1.36 293.

PB_0 EB_TO EB_LA EL_0 IL_0 RX1 RY1 RZ1 RZN AWNDO DOMEGA ELAS_OUT EASE_OUT EASE_OF6

700.0 8.60 0.00 0.00 0.00 0.100 0.000 0.985 0.080 0.200 1.0E-02 272.00 212.40 9.16

0.01Pbeam

(kW/ cc)

Ila s e r

( MW/ c m 2 )

10 Iase

(MW/ cm2 )

0 .1 %F2

0 .4 %F2

0 .7 %F2

Ore s t e s0 2 / 0 3

Calculated laser pulse profilesfor different F2 abundance.