Optical Train and Amplifier Staging for a KrF System

1
Optical Train and Amplifier Staging for a KrF
System

• Malcolm McGeoch
• PLEX LLC
• 20 Chapel St, C512
• Brookline, MA 02446
• 617-277-4480
• mcgeoch_at_xuv.com
• Tom Lehecka
• Penn State Electro-Optics Center
• [phone] X7118
• tml15_at_psu.edu
• Presented at
• High Average Power Laser Program Workshop
• University of Rochester LLE
• November 8th, 2005

2
Outline

• Design Baseline
• Optical layout
• Block diagram
• Amplifier staging
• Optical layout
• Diagnostic requirements
• Approximate optic count
• Target chamber layout
• Alignment Sensitivity

3
Summary of Baseline

• 500 kJ system KrF 248 nm
• 2.5 ns pulse length on target
• Twenty - 25 kJ amplifier modules
• Ninety beams per amplifier
• 16 X 16 cm output beams ? 1.1 J/cm2
• Forty beam clusters on target

4
Optical Block Diagram
Front End
Target Area
Amplifiers
5
Simplified ISI Diagram
Amplifiers are located at Fourier transform plane
of object aperture Fourier transform plane is
image relayed through the optical system

• Each diffraction limited point at the object
  aperture sees the same gain region at the
  amplifier
• Illumination on target is a magnified (or
  demagnified) image of the object aperture
• Zooming is achieved by changing the size of the
  object aperture
• Laser bandwidth provides temporal smoothing of
  speckle

6
E-beam Amp area optics
Input from multiplexing
Amp 2
Amp 1
Output to demultiplexing

• Single lens image relay from amp 2 to amp 1
• Output beam size of 16x16 cm yields fluence of
  1.09 J/cm2 on optics

7
Optical System Highlights

• Beam propagation in vacuum
• Eliminate linear and nonlinear optical effects
• Maintain cleanliness
• Two fully multiplexed (90 beams) e-beam
  amplifiers
• Amp 2 Electra size, 1 kJ
• Amp 1 25 kJ needs development
• Fourier transform plane imaged at all amplifiers
• XDL baseline 76 at initial zoom

8
Optics Count/sizing

• Estimate of optics for baseline 500 kJ design.
• Likely to increase 25 to accommodate physical
  layout
• At estimated cost of 20/cm2 this yields 125M
  in optics (without the 25 growth)

9
Laser diagnostics
1.) Laser energy Measure every beam Energy
transport efficiency monitor - amp to target 2.)
Laser Pulseshape Every beam Main
pulse ASE Beam to beam scatter 3.) Optic
damage and cleanliness monitor 4.) Focal spot
size Wavefront monitor Spot size

• We have just begun defining the laser diagnostic
  requirements

10
Facility Layout
205 m

• Twenty beamline system, one spare amp per side

11
Target Chamber Layout
Lens
Lens
GIMM
Mirror
Lens
First Wall Radius 5.5 m

• Forty beam ports, forty beams on target.
• CaF2 lens and dielectric mirror behind neutron
  shielding

12
Target Chamber Layout
Path from lens to target, Straightened out for
clarity
Dielectric mirrors
Lenses
GIMM, 15 segments
Dielectric mirrors
GIMM
Lens
13
Forty beam Uniformity
RMS non-uniformity on target ()

• Ratio of laser spot diameter to target
  diameter
• N Exponent of hyper Gaussian beam shape

• Penalty for 40 beams is small fewer beams
  preferred.

14
Alignment Sensitivity

• Penalty for 40 beams is small fewer beams
  preferred.
• 4 alignment error 1 non-uniformity ? 80 mm for
  2 mm target

15
Summary

• We are focusing design efforts on a 500 kJ KrF
  system
• Based on work at PLEX LLC, Penn State EOC and NRL
  we are baselining
• 500 kJ total laser energy
• 25 kJ per amplifier module simplified amplifier
  staging
• 2.5 ns pulse on target
• 40 beam clusters on target
• Low fluence beam propagation for higher
  reliability