1. Study of Photonic Band-Gap (PBG) Crystals and Their Defects
Elliott C. Johnson
Mentor: Jim Spencer
SULI Program 2007

2. Acceleration Research Department (ARD)
Research for accelerator technology
Development of existing facilities
Work towards next generation colliders
Design of new methods for particle acceleration
Laser-driven dielectric (PBG) structures

3. Photonic Band-Gap Crystals
The familiar electronic crystal:
A periodic array of atoms forms a lattice
Lattice arrangement defines energy bands
The optical analogy--a Photonic Band-Gap (PBG) Crystal:
A periodic array of optical materials forms a lattice
Allowed energy (wavelength) bands arise

4. PBGs for Particle Acceleration
Introduced defects confine modes spatially to one capillary.
In this way, a longitudinal E field can be generated down the fiber.
This arrangement, with a defect diameter of about 1.3 m is called the Lin configuration.
Why?
Smaller accelerator structures means stronger field, and thus higher energy gradient at less cost.

5. PBG Sample Characterization
Quality Assurance
Machining defects in 100 um dia capillary fiber.

6. Sample Characterization, Cont’d…
Wire measurements
25 um wire over 100 um dia capillary fiber
193 um wire in 250 um dia capillary fiber

7. Sample Characterization, cont’d…
Transmission Tests

8. Searching for higher-order modes in the Lin configuration
Previous to this work, only one mode (the lowest-order, “fundamental” case) had been studied in detail
The band-gap diagram suggests other modes suitable for acceleration may exist
Goal: try to find higher-order modes, and compare any found modes to the fundamental mode

9. Mode Search & Simulation
Simulations done with CUDOS Multistructured Optical Fiber Utilities (Univ. of Sydney)
Parameters for the Lin configuration were used with wavelengths corresponding to the band-gaps crossing the speed of light line
Many lattice modes were easily found, but finding acceleration modes took tiny variations in wavelength, and extra patience
…As opposed to lattice modes such as this:

10. Accelerating Modes Found!

11. Comparison of New Modes to Lin Mode

12. Future Work
Finding structures with a better defect radius to wavelength ratio
Need to invent a way to introduce a central defect into our samples, or possibly even fabricate our own PBG structures
Development of a laser-coupling system that doesn’t interfere with the electron beam

13. Acknowledgements Jim Spencer, Bob Noble, and the rest of the ARDB Crew
DOE
SULI Folks