1. Woodpile Structure Fabrication for Laser Acceleration at E163
Chris McGuinness
Stanford – SLAC
AARD
ARD Seminar 02/03/09

2. Outline Gradient Woodpile Structure Fabrication
4 Layer Structure Analysis
FTIR Spectroscopy Measurements
Simulations
Conclusion
Where things are at for E163
Future Experiments

3. Gradient ?

4. Damage Fluence λ=800nm o Silicon
M. Mero, et. al. Phys. Rev. B (2005)
λ=800nm
D.M. Simanovskii, et. al. PRL (2003)
Ben Cowan, Stanford Graduate Thesis (2007)
o Silicon

5. Woodpile Band Diagram

6. Dielectric Accelerator Structures
Gratings
PBG Fibers
3D Photonic Crystal (Woodpile)
Thorlabs HC
Damage impedence = Eacc^2/2umax*c = 6.1ohms
Characteristic Impedence = Eacc^2*lambda^2/P = 460ohms

7. Accelerating Mode
Top View
Ratio=1.41
Side View
Front View

8. Gradient SiO2 Eacc=2.76 GV/m @800nm(3.75e5GHZ) ZnS Eacc=1.04 GV/m
101
SiO2 Eacc=2.76 GV/m
@800nm(3.75e5GHZ)
ZnS Eacc=1.04 GV/m
@5μm(6e4GHZ)
Al3O2 Eacc=2.0 GV/m
@800nm(3.75e5GHZ)
Si Eacc=337 MV/m
@1550nm(1.94e5GHZ)

9. Outline Gradient Woodpile Structure Fabrication
4 Layer Structure Analysis
FTIR Spectroscopy Measurements
Simulations
Conclusion
Where things are at for E163
Future Experiments

10. Woodpile Structure Parameter Scaling* w=.2757a h=.3486a λ=2.703a
w=500nm
λ=4.9μm
a=1.814
h=632nm
Δ=91nm
w=300nm
λ=2.94μm
a=1.09μm
h=379nm
Δ=54nm h w a Δ
*Cowan, B. “Photonic Crystal Laser-Driven Accelerator Structures”
(PhD dissertation Stanford University 2007) 77.

11. Fabrication Process Step 1: SiO2 Deposition Uniformity = 1-2%
resist
Silicon Substrate
Si Substrate
Photo resist 1 2 h
SiO2
Step 1: SiO2 Deposition
Uniformity = 1-2%
Step 2: Resist Coat
Step 3: Optical Lithography
Minimum feature size 450nm
Alignment 3σ=60nm
Step 4: Dry etch SiO2
Step 5: Poly-si Deposition 4 3 w a 5
Poly-si
Silicon Substrate
SiO2
poly-si

12. Fabrication Process Step 6: Chemical Mechanical Polish
Time
Frictional Force
10sec=15nm 6
Step 6: Chemical Mechanical Polish
Step 7: Repeat process for remaining layers
Final Step: Oxide Etch
SiO2
poly-si 7 8

13. Completed Four Layer Test Structure
October 2008

14. Outline Gradient Woodpile Structure Fabrication
4 Layer Structure Analysis
FTIR Spectroscopy Measurements
Simulations
Conclusion
Where things are at for E163
Future Experiments

15. FTIR Spectroscopy Measurements

16. Simulation Using MPB

17. Finite Thickness Simulation Reflection/Transmission (averaged over S&P polarizations, and polar angle θ, φ=0)

18. Simulation Reflection/Transmission (averaged over S&P polarizations, and polar angle θ, φ=0)

19. Simulation vs. Measurement
Bandgap from MPB

20. SEM Profile Images

21. Simulation vs. Measurement
Bandgap from MPB

22. Summary Completed the fabrication of a four layer test structure
Verified a process which will be used for the fabrication of a 15 layer structure with a defect
Taken Spectroscopy measurements
Developed simulation tools that agree well measurements

23. Current State and Future of E163
Phase 1: Characterize laser/electron energy exchange in vacuum
Phase 2: Demonstrate optical bunching and acceleration
Phase 3: Test multicell lithographically produced structures

24. Future Experiments Fabrication Experiments
15 layer structure with defect
Couplers
Focusing Elements
Experiments
Wakefield
Measure modes excited by
bunched electron beam
Excite defect
Measure mode profile
Measure coupling efficiency
Net Acceleration

25. Acknowledgments E163 Collaboration Byer Group NLCTA Operators
Bob Siemann, Eric Colby, Chris Sears, Ben Cowan, Joel England, Bob Noble, Jim Spencer
Byer Group
Bob Byer, Tomas Plettner, Alex Serpry, Patrck Liu
NLCTA Operators
Janice Nelson, Doug McCormick
Stanford Nanofab
Mary Tang, Mahnaz Mansourpour, Maurice Stevens, Ed Myers, Uli Thumser, Nancy Latta

26. THIS IS THE END