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Title: Coupler Studies for PBG Fiber Accelerators

Abstract

Photonic band gap (PBG) fiber with hollow core defects are being designed and fabricated for use as laser driven accelerators because they can provide gradients of several GeV/m for picosecond pulse lengths. We expect to produce fiber down to {lambda} = 1.5-2.0 {micro}m wavelengths but still lack a viable means for efficient coupling of laser power into such structures due to the very different character of the TM-like modes from those used in the telecom field and the fact that the defect must function as both a longitudinal waveguide for the accelerating field and a transport channel for the particles. We discuss the status of our work in pursuing both end and side coupling. For both options, the symmetry of these crystals leads to significant differences with the telecom field. Side coupling provides more options and appears to be preferred. Our goals are to test gradients, mode content and coupling efficiencies on the NLCTA at SLAC. While there are many potential types of fiber based on very different fabrication methods and materials we will concentrate on 2D axisymmetric glass with hexagonal symmetry but will discuss several different geometries including 2D and 3D planar structures. Since all of these can bemore » fabricated using modern techniques with a variety of dielectric materials they are expected to have desirable optical and radiation hardness properties. Thus, we expect a new generation of very high gradient accelerators that extends the Livingston-Panofsky chart of exponential growth in energy vs. time at greatly reduced costs. For illustration, Fig.1 shows a simulation of our first engineered fiber with an accelerating mode expected near 7.3 {micro}m that is now ready to test on the NLCTA. In this example, one sees the uniform longitudinal accelerating field in the central defect as first shown by Lin3 together with a hexagonal array of surrounding hot spots. Contrary to what one expects from the telecom field, Ng et al. have shown4 that the ideal end-coupling scheme for this structure appears as shown in Fig. 2 with a six-fold array of laser spots focused inside the end of the fiber. While convenient for an on-axis particle beam, this is inconvenient for the laser drive field as well as the tolerances it places on the end cleave of the fiber. The importance of the crystal symmetry is clearly shown so that one might expect side coupling to reflect a similar pattern which we find that it does unless the hexagonal symmetry is perturbed sufficiently. This can be done in several ways and will be discussed further.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1022522
Report Number(s):
SLAC-PUB-14440
TRN: US1104256
DOE Contract Number:  
AC02-76SF00515
Resource Type:
Conference
Resource Relation:
Conference: Presented at 2011 Particle Accelerator Conference (PAC'11), New York, NY, 28 Mar - 1 Apr 2011
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; 36 MATERIALS SCIENCE; ACCELERATORS; DEFECTS; DIELECTRIC MATERIALS; FABRICATION; FIBERS; GLASS; HARDNESS; HOT SPOTS; LASERS; PARTICLE BEAMS; RADIATIONS; SIMULATION; STANFORD LINEAR ACCELERATOR CENTER; SYMMETRY; TRANSPORT; WAVEGUIDES; WAVELENGTHS; Accelerators,ACCPHY

Citation Formats

England, J, Ng, C, Noble, R, Spencer, J, Wu, Z, Xu, D, and /SLAC. Coupler Studies for PBG Fiber Accelerators. United States: N. p., 2011. Web.
England, J, Ng, C, Noble, R, Spencer, J, Wu, Z, Xu, D, & /SLAC. Coupler Studies for PBG Fiber Accelerators. United States.
England, J, Ng, C, Noble, R, Spencer, J, Wu, Z, Xu, D, and /SLAC. Wed . "Coupler Studies for PBG Fiber Accelerators". United States. https://www.osti.gov/servlets/purl/1022522.
@article{osti_1022522,
title = {Coupler Studies for PBG Fiber Accelerators},
author = {England, J and Ng, C and Noble, R and Spencer, J and Wu, Z and Xu, D and /SLAC},
abstractNote = {Photonic band gap (PBG) fiber with hollow core defects are being designed and fabricated for use as laser driven accelerators because they can provide gradients of several GeV/m for picosecond pulse lengths. We expect to produce fiber down to {lambda} = 1.5-2.0 {micro}m wavelengths but still lack a viable means for efficient coupling of laser power into such structures due to the very different character of the TM-like modes from those used in the telecom field and the fact that the defect must function as both a longitudinal waveguide for the accelerating field and a transport channel for the particles. We discuss the status of our work in pursuing both end and side coupling. For both options, the symmetry of these crystals leads to significant differences with the telecom field. Side coupling provides more options and appears to be preferred. Our goals are to test gradients, mode content and coupling efficiencies on the NLCTA at SLAC. While there are many potential types of fiber based on very different fabrication methods and materials we will concentrate on 2D axisymmetric glass with hexagonal symmetry but will discuss several different geometries including 2D and 3D planar structures. Since all of these can be fabricated using modern techniques with a variety of dielectric materials they are expected to have desirable optical and radiation hardness properties. Thus, we expect a new generation of very high gradient accelerators that extends the Livingston-Panofsky chart of exponential growth in energy vs. time at greatly reduced costs. For illustration, Fig.1 shows a simulation of our first engineered fiber with an accelerating mode expected near 7.3 {micro}m that is now ready to test on the NLCTA. In this example, one sees the uniform longitudinal accelerating field in the central defect as first shown by Lin3 together with a hexagonal array of surrounding hot spots. Contrary to what one expects from the telecom field, Ng et al. have shown4 that the ideal end-coupling scheme for this structure appears as shown in Fig. 2 with a six-fold array of laser spots focused inside the end of the fiber. While convenient for an on-axis particle beam, this is inconvenient for the laser drive field as well as the tolerances it places on the end cleave of the fiber. The importance of the crystal symmetry is clearly shown so that one might expect side coupling to reflect a similar pattern which we find that it does unless the hexagonal symmetry is perturbed sufficiently. This can be done in several ways and will be discussed further.},
doi = {},
url = {https://www.osti.gov/biblio/1022522}, journal = {},
number = ,
volume = ,
place = {United States},
year = {2011},
month = {8}
}

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