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^{1,a)}, René Beigang

^{2}and Marco Rahm

^{1}

### Abstract

We designed, fabricated, and optically characterized single and double layer metamaterial-based gradient index beam steerers for terahertz radiation. We measured a maximal deflection angle of 6°. The operation bandwidth of the beam steerers was 300 GHz around a center frequency of 1.3 THz. Within this bandwidth, the amplitude transmission was higher than 50%. Due to a thickness of only 100 μm or below, the implemented beam steerers are ideally suited for integration in compact terahertz measurement systems.

We acknowledge financial support from the Federal Ministry of Education and Research (Grant No. FKZ: 13N11905) and the German Science Foundation (Grant No. FKZ: RA 1903/2-2). Furthermore, we acknowledge technical support by the Nano Structuring Center (NSC) at University of Kaiserslautern.

### Key Topics

- Terahertz radiation
- 13.0
- Refractive index
- 11.0
- Metamaterials
- 8.0
- Electric fields
- 7.0
- Polarization
- 7.0

## Figures

(a) Unit cell of the beam steerer. A 3 μm slit was inscribed in a 200 nm thick copperplate. The copper was embedded in 60 μm thick BCB. (b) Retrieved effective refractive index n and transmission T versus frequency for different inner ring radii r in . r in was increased in 1 μm steps from 18 μm (black line) to 25 μm (yellow-gray line, highest n). (c) Refractive index versus the inner ring radius r in at the design frequency 1.3 THz (black square) as well as 1.2 THz (red circle) and 1.4 THz (blue triangle). Straight line shows fit with fixed slope of . (d) Excerpt of a microscope picture of the fabricated beam steerer. The ring radius increases along the x-axis from left to right.

(a) Unit cell of the beam steerer. A 3 μm slit was inscribed in a 200 nm thick copperplate. The copper was embedded in 60 μm thick BCB. (b) Retrieved effective refractive index n and transmission T versus frequency for different inner ring radii r in . r in was increased in 1 μm steps from 18 μm (black line) to 25 μm (yellow-gray line, highest n). (c) Refractive index versus the inner ring radius r in at the design frequency 1.3 THz (black square) as well as 1.2 THz (red circle) and 1.4 THz (blue triangle). Straight line shows fit with fixed slope of . (d) Excerpt of a microscope picture of the fabricated beam steerer. The ring radius increases along the x-axis from left to right.

(a) Electric field of a 1.3 THz beam deflected from a double-layer beam steerer. The beam was deflected by –6.1°. (b) Spectral amplitude transmission of a single- and double-layer beam steerer for two different orthogonal polarizations in x- and y-direction.

(a) Electric field of a 1.3 THz beam deflected from a double-layer beam steerer. The beam was deflected by –6.1°. (b) Spectral amplitude transmission of a single- and double-layer beam steerer for two different orthogonal polarizations in x- and y-direction.

(a) Measured (symbols) and numerically calculated (lines) lateral THz field intensity distributions in dependence on the distance z from a single-layer beam deflector at 1.3 THz for a y-polarized beam. x = 0 corresponds to the center position of the non-deflected reference beam. (b) Dependence of the beam center position on the distance z from the beam steerer as derived from (a). Symbols correspond to measured data and lines to numerical data. The blue triangles and line correspond to deflection from a beam steerer that was rotated by 180° around the z-axis. Black squares and line indicate a reference measurement without beam deflector.

(a) Measured (symbols) and numerically calculated (lines) lateral THz field intensity distributions in dependence on the distance z from a single-layer beam deflector at 1.3 THz for a y-polarized beam. x = 0 corresponds to the center position of the non-deflected reference beam. (b) Dependence of the beam center position on the distance z from the beam steerer as derived from (a). Symbols correspond to measured data and lines to numerical data. The blue triangles and line correspond to deflection from a beam steerer that was rotated by 180° around the z-axis. Black squares and line indicate a reference measurement without beam deflector.

Beam center position versus distance z from a double-layer beam steerer for (a) y-polarization and (b) x-polarization.

Beam center position versus distance z from a double-layer beam steerer for (a) y-polarization and (b) x-polarization.

Measured and numerically calculated spectral dependence of the beam deflection angle for x- and y-polarized incident beams in the case of a (a) single-layer beam steerer and (b) double-layer beam steerer.

Measured and numerically calculated spectral dependence of the beam deflection angle for x- and y-polarized incident beams in the case of a (a) single-layer beam steerer and (b) double-layer beam steerer.

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