Naval Research Laboratory

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NRL J. Sethian M. Myers J. Giuliani R.
Lehmberg S. Obenschain SAIC M. Wolford R.
Jaynes Commonwealth Tech F. Hegeler M.
Friedman RSI P. Burns S. Searles
KrF Lasers Electra Laser Overview
Naval Research Laboratory Plasma Physics
Division Washington, DC 20375 13th HAPL
Meeting November 8, 2005 University of
Rochester (LLE) Work supported by DOE/NNSA/DP
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Electra KrF Laser Layout
pre-amp 10 cm x 10 cm
main amp 30 cm x 30 cm
seed osc 1cm x 3 cm
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Electra 30 cm x 30 cm Amplifier stage
Electra title page
730 J Plano-Parallel Oscillator 100 ns FWHM
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E-Beam KrF Pump Source
500 kV, 110 kA 140 ns pulse
Discharging through the 112 step-up transformer
Charging of the PFL to 1 MV (3-4 ms)
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Electra Foil Cooling Concepts
Foil Cooling concepts being examined
See Georgia Tech Poster on Investigation of Mist
Cooling for the Electra Hibachi Demonstrated 5
Hz at full power for 10,000 shots continuous in
module See John Giuliani Poster Foil Cooling
for electron beam pumped KrF lasers
Louvers
Thermal Conduction
Mist Cooling
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Laser resonator and Rep-Rate Diagnostics
All Optics Standard Grade Fused Silica 1F
Photodiodes
Pump Source (electrons)
Output Coupler
Mirror
Pickoff Window
Graphite Beam Dump
E-Beam Pumped Region (Gain Media) 1 m
Tilted Windows
Rear Mirror Photodiode
Pump Source (electrons)
Calorimeter Positions
Real Time F2 monitor with Nitrogen laser attached
to recirculator
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Electra KrF laser is very consistent in long
duration, repetitively pulsed, runs
300 J _at_ 1 Hz (300 W) 10,000 shots continuous (2.5
hrs)
700 J _at_ 1 Hz (700 W) 400 shots continuous
400 J _at_ 5 Hz (2000 W) 500 shots continuous
Notable results 7700 shots _at_ 5 Hz four back to
back runs 9600 shots _at_ 2.5 Hz in a multiple
segmented run
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Intrinsic Efficiency 730 J Laser Shot
E-Beam Power
PLaser (GW)
PE-beam (GW)
Time (ns)
E-Beam Power (Pressure Rise (E)Radiation
Correction (105)) Laser Energy
(E) Distributed over the pulse width measured
in the diode
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How we project an amplifier intrinsic efficiency
of 11-12 based on oscillator results of 9.6

• Better windows (gt99 transmitting vs. measured
  93 transmission in oscillator)
• Anti-Reflection coating on both side windows
• (currently single sided)
• KrF or ArF grade (currently standard grade
  fused silica)
• Utilization of Rigrod analysis implies an
  expected increase of 17 in efficiency(
  )

A properly designed amp would have

• Lower laser light absorption due to fluorine,
  less passes through e-beam unpumped regions (2)

• Full laser extraction of the created gain media,
  data here is 31.5 cm deposition in electron beam
  propagation direction and utilization of a 30 cm
  laser extracting (4-5)

• Amplification from input laser, no oscillator
  build-up time (1)

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Intrinsic Efficiency Data (optimal conditions
highlighted)
Composition And Pressure ELaser EE-Beam ELaser/ EE-Beam ?int Flat-top ELaser Flat-top EE-Beam Flat-top ?int Expected Ideal Amplifier ?int
60 Ar, 39.7 Kr, 0.3 F2 , _at_ 16 psi 685 J 7.89 kJ 8.7 506 J 5.41 kJ 9.4 11.7
60 Ar, 39.7 Kr, 0.3 F2 , _at_ 20 psi 731 J 8.78 kJ 8.3 574 J 6.01 kJ 9.6 11.9
60 Ar, 39.7 Kr, 0.3 F2 , _at_ 24 psi 711 J 9.42 kJ 7.5 572 J 6.45 kJ 8.9 11.1
60 Ar, 39.7 Kr, 0.3 F2 , _at_ 28 psi 660 J 9.75 kJ 6.8 551 J 6.68 kJ 8.2 10.3
80 Ar, 19.7 Kr, 0.3 F2 , _at_ 22 psi 731 J 9.00 kJ 8.1 559 J 6.17 kJ 9.1 11.3
72.4 Ar, 17.8 Kr, 9.5 He, 0.27 F2 ,_at_ 24.3 psi 718 J 9.02 kJ 8.0 569 J 6.18 kJ 9.2 11.5
66.7 Ar, 16.4 Kr, 16.7 He, 0.25 F2 ,_at_ 26.4 psi 693 J 9.23 kJ 7.5 556 J 6.32 kJ 8.8 11.0
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Gain Media Uniformity Measurements(Single Pass
Gain)
248 nm bandpass filter
Parasitic Light Attenuators
Neutral Density Filter
KrF output
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Photodiode (1 ns risetime)
Iin
Iout
PD2
PD3
ND
E-Beam Pumped Region
KrF input
PD1
PD4
Beam Cube Polarizer
Gas Composition 60 Ar, 39.7 Kr, 0.3 F2
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Uniform Amplification Gain Across the entire 30
cm x 30 cm aperture _at_ 20 psi
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Addition of He does not significantly reduce
output . Increases foil cooling
Single Pass Gain (Amplifier) results and
Oscillator results
Output Gas Composition
731 J 80 Ar, 19.7 Kr
718 J Added 10 He
693 J Added 20 He
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KrF Laser Calculations (Orestes)
e-beam ionization and excitation from Boltzmann
analysis. plasma 1D axially resolved, separate
electron and gas temperatures, enthalpy
balance. kinetics 24 species, 144 reactions,
Includes KrF vibrational structure. lasing
method of characteristics. ASE 3D, discrete
ordinates, time dependent, ASE gain narrowing.
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Kinetics Change Explains Fluorine Concentration
Reactants Super-Elastic Dissociative Attachment
eKrF KrFe KrF-
e
e
e
e
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KrF Kinetics Calculations (Orestes) Agree with
Experiment
9 8 7 6 5 4 3 2 1 0
Pe-beam (expt) ILaser (expt) ILaser
(Orestes) Shot OSC080404_11 ELaser
731 Joules
Pe-beam (100 kw/cc) ILaser (MW/cm2)
0 50 100
150 200 250
time (ns)
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Orestes has been used to predict the performance
of a 25 kJ amplifier
four e-beams per side 800 kV 200 kA 225
nsec 100 x 50 cm each
40 cm
100 x 100 cm window
10 cm
1.1 atm, 40 Kr, 0.35 F2 TWIN 99, RMIR
100 210 kJ e-beam deposition flat (250 kJ
total) PEB 526 kW/cc (105 J/liter) in flat
portion Laser EIN(t1 to t2) 1.0 kJ Laser
EOUT(t1 to t2) 27.4 kJ (32.4 kJ
total) Intrinsic Efficiency(t1 to t2) 13.0
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Key stresses in the 25 kJ KrF amplifiers are
within existing Electra and Nike parameters
25 kJ Laser Amplifier
Marx
1st stage
1st Mag Switch
2nd stage (PFL)
TTI
2nd Mag Switch
Laser Cell
25 kJ Nike Electra E-beam
voltage (kV) 800 640-750
500 E-beam pulse (ns) 225 225
140 Cathode size (cm) 50 x 100 60 x
200 30 x 100 5 Hz Foil Load (W/cm2) 4.1
N/A 4.1 Pump Power (kW/cc) 526
326-430 700 Window Load (J/cm2)
2.5 1.0 0.78
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Summary

• Measured flat-top intrinsic efficiency of 9.6
  with an oscillator yield of 731 J Yield, plus
  advances in pulsed power and hibachi gives a
  basis for the projection of 7 wall plug
  efficiency in amplifier configuration
• Orestes Code agrees with Electra Oscillator
  measurements over wide range of parameter space
  (F2 concentration, pressure dependence, absolute
  yield)
• 3) 2.5 hour operation rep-rate (durability, with
  high reproducibility) at 1 Hz with 5 Hz
  capability
• 4) Gain Media Uniformity over entire 30 cm x 30
  cm has been measured