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

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

Gradient ?

Damage Fluence λ=800nm o Silicon M. Mero, et. al. Phys. Rev. B 71 115109 (2005) λ=800nm D.M. Simanovskii, et. al. PRL 91 107601 (2003) Ben Cowan, Stanford Graduate Thesis (2007) o Silicon

Woodpile Band Diagram

Dielectric Accelerator Structures Gratings PBG Fibers 3D Photonic Crystal (Woodpile) Thorlabs HC-1550-2 Damage impedence = Eacc^2/2umax*c = 6.1ohms Characteristic Impedence = Eacc^2*lambda^2/P = 460ohms

Accelerating Mode Top View Ratio=1.41 Side View Front View

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)

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

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.

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

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

Completed Four Layer Test Structure October 2008

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

FTIR Spectroscopy Measurements

Simulation Using MPB

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

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

Simulation vs. Measurement Bandgap from MPB

SEM Profile Images

Simulation vs. Measurement Bandgap from MPB

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

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

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

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

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