Bragg reflection waveguides with a matching layer

Abstract

It is demonstrated that Bragg reflection waveguides, either planar or cylindrical, can be designed to support a symmetric mode with a specified core field distribution, by adjusting the first layer width. Analytic expressions are given for this matching layer, which matches between the electromagnetic field in the core, and a Bragg mirror optimally designed for the mode. This adjustment may change significantly the characteristics of the waveguide. At the particular wavelength for which the waveguide is designed, the electromagnetic field is identical to that of a partially dielectric loaded metallic or perfect magnetic waveguide, rather than a pure metallic waveguide. Either a planar or coaxial Bragg waveguide is shown to support a mode that has a TEM field distribution in the hollow region.

Dielectric laser accelerators

“…These concepts are applied to 2D structures in , Litchinitser et al (2003), Couny et al (2007), and Murao et al (2011). Because Bragg reflectors can be understood through both interference conditions and the PBG condition, their application to acceleration, first explored in Mizrahi and Schachter (2004a), is particularly illuminating, and is discussed in detail in Section III.B.…”

“…Motivated by the requirement v ph = c, Mizrahi and Schachter (2004a) have developed a general method for designing the Bragg waveguide for a given phase velocity, given the core dimension and a set of dielectric materials. The core dimension itself may be dictated by other considerations, such as the maximum field allowed to prevent material breakdown, beam dynamics, and the interaction efficiency.…”

“…where ∆ 1 is the first layer width, and Z 1 , Z 2 are the transverse impedances of the first and second layers, respectively (Mizrahi and Schachter, 2004a). Setting the first layer width according to the above condition will ensure that the required mode at the given wavelength will indeed be supported by the waveguide.…”

“…However, in order to attain efficient acceleration that is scalable to high energies, it is necessary to take advantage of the high laser damage thresholds and low ohmic losses of dielectric materials. To these ends, a variety of all-dielectric high-gradient laser-accelerator structures have been proposed in recent years (Cowan, 2008;Lin, 2001;Mizrahi and Schachter, 2004a;Naranjo et al, 2012;Plettner et al, 2006). Significant progress in the communication industry for high-power solid-state lasers, optical fibers, and photo-lithographic techniques developed by the semi-conductor industry have enabled the first of these dielectric laser accelerator prototypes to be fabricated at the micron scale and tested with particle beams, leading to the first high-gradient demonstrations of laser acceleration in these devices (Peralta et al, 2013).…”

Bragg accelerator optimization

“…For an optical accelerator having a vacuum core, the surrounding layers must have, at the operating wavelength, an effective dielectric coefficient smaller than unity, i.e., ε eff < 1, thus creating the need for a Bragg structure with a matching layer [3] . The present study is organized as follows: A selfconsistent solution for maximum gradient is presented in Section 2.…”