This paper develops a quasi-analytical and self-consistent model to compute the polarizabilities of split ring resonators (SRRs). An experimental setup is also proposed for measuring the magnetic polarizability of these structures. Experimental data are provided and compared with theoretical results computed following the proposed model. By using a local field approach, the model is applied to the obtaining of the dispersion characteristics of discrete negative magnetic permeability and left-handed metamaterials. Two types of SRRs, namely, the so-called edge coupled- and broadside coupled- SRRs, have been considered. A comparative analysis of these two structures has been carried out in connection with their suitability for the design of metamaterials. Advantages and disadvantages of both structures are discussed.

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Comparative analysis of edge- and broadside- coupled split ring resonators for metamaterial design - theory and experiments

The resolution of conventional optical lens systems is always hampered by the diffraction limit. Recent developments in artificial metamaterials provide new avenues to build hyperlenses and metalenses that are able to image beyond the diffraction limit. Hyperlenses project super-resolution information to the far field through a magnification mechanism, whereas metalenses not only super-resolve subwavelength details but also enable optical Fourier transforms. Recently, there have been numerous designs for hyperlenses and metalenses, bringing fresh theoretical and experimental advances, though future directions and challenges remain to be overcome.

/pdf/hyperlenses-and-metalenses-for-far-field-super-resolution-3h8v1zh6s8.pdf

Hyperlenses and metalenses for far-field super-resolution imaging

Materials engineered to have negative permittivity and permeability demonstrate exotic behavior, from a negative refractive index to subwavelength focusing.

https://physicstoday.scitation.org/doi/pdf/10.1063/1.1784272

Reversing Light With Negative Refraction

We study both theoretically and experimentally the transmission properties of a lattice of split ring resonators (SRRs) for different electromagnetic (EM) field polarizations and propagation directions. We find unexpectedly that the incident electric field E couples to the magnetic resonance of the SRR when the EM waves propagate perpendicular to the SRR plane and the incident E is parallel to the gap-bearing sides of the SRR. This is manifested by a dip in the transmission spectrum. A simple analytic model is introduced to explain this interesting behavior.

/pdf/electric-coupling-to-the-magnetic-resonance-of-split-ring-2ash9u8xou.pdf

Electric coupling to the magnetic resonance of split ring resonators

We investigate the magnetic resonance of split-ring resonators (SRR) experimentally and numerically. The dependence of the geometrical parameters on the magnetic resonance frequency of SRR is studied. We further investigate the effect of lumped capacitors integrated to the SRR on the magnetic resonance frequency for tunable SRR designs. Different resonator structures are shown to exhibit magnetic resonances at various frequencies depending on the number of rings and splits used in the resonators.

/pdf/investigation-of-magnetic-resonances-for-different-split-3ay3wb7hdf.pdf

Investigation of magnetic resonances for different split-ring resonator parameters and designs

A plano-concave lens with negative index of refraction has been designed and fabricated. Such lenses have been postulated for many years, but only recently has their realization been made possible through improved simulation and fabrication procedures. We report here the simulation, fabrication, and performance of such a lens. The lens images the source field and reproduces the results of standard Gaussian optics. The curved lens with negative index of refraction in the microwave frequency region of the electromagnetic spectrum has been compared to a plano-convex Macor positive index of refraction lens having the same radius of curvature.

Performance of a negative index of refraction lens

Using numerical simulation techniques, the transmission and reflection coefficients, or S parameters, for left-handed metamaterials are calculated. Metamaterials consist of a lattice of conducting, nonmagnetic elements that can be described by an effective magnetic permeability μeff and an effective electrical permittivity eeff, both of which can exhibit values not found in naturally occurring materials. Because the electromagnetic fields in conducting metamaterials can be localized to regions much smaller than the incident wavelength, it can be difficult to perform accurate numerical simulations. The metamaterials simulated here, for example, are based on arrays of split ring resonators (SRRs), which produce enhanced and highly localized electric fields within the gaps of the elements in response to applied time dependent fields. To obtain greater numerical accuracy we utilize the newly developed commercially available code MICROWAVE STUDIO, which is based on the finite integration technique with the per...

/pdf/ab-initio-numerical-simulation-of-left-handed-metamaterials-33vp3i0mbc.pdf

Ab initio numerical simulation of left-handed metamaterials: Comparison of calculations and experiments

This paper describes pulse compression and energy recovery experiments using an RF photocathode gun and injector accelerator at a fundamental RF of 433 MHz (1f) and a third-harmonic RF accelerator section operating at 1300 MHz (3f). For pulse compression, the 3f section is used both to program the energy slew and correct for RF-induced curvature in the electron beam micropulse which is subsequently compressed in a non-isochronous, three-dipole chicane. A compression factor of six has been obtained for a micropulse charge of 3 nC. Both the transverse and longitudinal emittances were measured for the compressed pulse. In the energy recovery experiment, the photocathode drive laser pulse is split into two pulses separated in time such that the resulting electron pulses are both accelerated by the 1f accelerator, while the 3f section simultaneously decelerates one pulse and accelerates the other. This is achieved by placing the two micropulses on either side of the zero crossing of the 3f RF waveform. The results of both experiments will be discussed.

Results of the Boeing pulse compression and energy recovery experiments

The design for a potential free electron laser (FEL), driven by a 120-MeV linac capable of generating 0.1-A macropulse average current beams at a duty factor of 0.6%, is described. The accelerator will employ a photo-injected, 18-MeV, 433-MHz linac as an injector, followed by a 1300-MHz longitudinal phase space "linearizer", a magnetic buncher, and seven sections of 1300-MHz, pulsed traveling wave linac structure. Pulse lengths of 7 ps will be attained with minimal distortion of the pulse profile and normalized 90% emittance of 30/spl plusmn/10 /spl pi/-mm-mr. The magnets used to transport the beam from the linac to the FEL centerline, the wiggler, and the optical resonator will be reclaimed from previous FEL demonstration experiments.

/pdf/a-kilowatt-class-visible-free-electron-laser-facility-4hd2ymiebw.pdf

A kilowatt class visible free electron laser facility

An 18 MeV photocathode accelerator, consisting of a two-cell RF photocathode injector (previously operated at 27 MHz micropulse repetition frequency, 5 nC micropulse charge, and 25% duty factor [D.H. Dowell et al., Appl. Phys. Lett. 63 (1993) 2035]) followed by four new multicell cavities, all operating at 433 MHz, is currently being tested for FEL applications. In the present experiment, the inclusion of a third harmonic RF linearizer (operating at 1300 MHz) will allow tailoring of flat-topped micropulse shapes with high peak current. This pulse shaping leads to optimal FEL efficiency and is discussed in another contribution to this conference [J.L. Adamski et al.]. The 1300 MHz structure can also be used in a simple experiment to investigate energy recovery for high power and high efficiency FELs. In this case, proper RF phasing of the drive laser micropulses will allow the 1300 MHz accelerator section to simultaneously accelerate and decelerate alternate micropulses. Longitudinal phase space preparation for both experimental modes is discussed.

A.M. Vetter

Papers

Performance of a negative index of refraction lens

Ab initio numerical simulation of left-handed metamaterials: Comparison of calculations and experiments

Results of the Boeing pulse compression and energy recovery experiments

A kilowatt class visible free electron laser facility

The Boeing photocathode accelerator magnetic pulse compression and energy recovery experiment