We present photoconductive emitters and detectors for radially and azimuthally polarized terahertz beams.
Microstructured electrodes consisting of concentric rings serve as antennas for radially polarized beams. Electrode
patterns consisting of radially arranged segments are employed for the antennas for azimuthally polarized beams. A
second periodic structure is used to prevent destructive interference of THz wavelets of opposite polarization. Beam
profiles are detected for divergent beams in proximity to the emitter as well as for refocused beams. The THz beams
have a donut-like intensity distribution and the beam profiles can be quantitatively described as lowest order Bessel-
Gauss modes. Furthermore we demonstrate that detection antennas of similar patterning are selective for detection of
particular modes.
We present large-area emitters based on GaInAsN which show efficient THz emission for excitation wavelengths up to 1.35 μm. The substrate material consists of a 1000 nm
Ga1-yInyAs1-xNx (y = 0.11 and x = 0.04) layer grown by molecularbeam epitaxy on semi-insulating GaAs. On top there is an additional
GaAs/Al0.3Ga0.7As heterostructure with thicknesses of 5 nm for the GaAs and 60 nm for the AlGaAs layer, respectively. Transmission measurements with a Fourier
transform spectrometer reveal a bandgap corresponding to a wavelength of 1.5 μm. The resistance of a complete device
with an active area of 1 mm2 is 0.3 MΩThis allows operation with high bias fields (30 kV/cm) without being limited by
heating.
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