THz technology, THz vector beams

Photoconductive emitters excited with femtosecond laser pulses are a widely used source for single-cycle terahertz (THz) radiation pulses. By application of an interdigitated electrode geometry we have improved the emitter efficiency and THz output power significantly. To prevent destructive interference of THz wavelets generated by electrons that are accelerated in opposite directions, a second metallization (green in figure) prevents photogeneration of carriers in every second gap between the electrodes. Emitters based on this patented design are commercially available via the HZDR Innovation GmbH.

Scalable THz emitters offer freedom with respect to the electrode geometry. This can be used to generate modes that differ from the commonly used linearly polarized Gauss beams. We generated radially and azimuthally polarized THz beams by photoconductive emitters. Especially radially polarized beams have interesting properties. They can be focussed to smaller spot sizes as compared to linearly polarized beams and they exhibit longitudinal field components in the focus.

Using the non-polar material Ge instead of the typical III-V semiconductors as a photoconductive material results in extremely high THz bandwidth up to 70 THz due to the lack of a Reststrahlenband.

Related publications

A. Singh, M. Welsch, S. Winnerl, M. Helm, H. Schneider, Non-plasmonic improvement in photoconductive THz emitters using nano- and micro-structured electrodes, Optics Express 28, 35490 (2020)

A. Singh, A. Pashkin, S. Winnerl, M. Welsch, C. Beckh, P. Sulzer, A. Leitenstorfer, M. Helm, H. Schneider, Up to 70 THz bandwidth from implanted Ge photoconductive antenna excited by a fibre laser, Light: Science & Applications 9, 30 (2020)

A. Singh, A. Pashkin, S. Winnerl, M. Helm, H. Schneider, Gapless broadband terahertz emission from a germanium photoconductive emitter, ACS Photonics 5, 2718 (2018)

A. Singh, S. Winnerl, J. C. König-Otto, D. R. Stephan, M. Helm, H. Schneider, Plasmonic efficiency enhancement at the anode of strip line photoconductive terahertz emitters, Optics Express 24, 22628-22634 (2016)

K. J. Kaltenecker, J. C. Otto, M. Mittendorff, S. Winnerl, H. Schneider, M. Helm, H.P. Helm, M. Walther, B. M. Fischer, Gouy phase shift of a radially polarized Gaussian beam, Optica 3, 35 (2016)

M. Xu, M. Mittendorff, R. J. B. Dietz, H. Künzel, B. Sartorius, T. Göbel, H. Schneider, M. Helm, S. Winnerl, THz generation and detection with InGaAs-based large-area photoconductive devices excited at 1.55 µm, Appl. Phys. Lett. 103, 251114 (2013)

M. Mittendorff, M. Xu, R. J. B. Dietz, H. Künzel, B. Sartorius, H. Schneider, M. Helm, S. Winnerl, Large area photoconductive THz emitter for 1.55 µm excitation based on an InGaAs heterostructure, Nanotechnology 24, 214007 (2013)

S. Winnerl, R. Hubrich, M. Mittendorff, H. Schneider, M. Helm, Universal phase relation between longitudinal and transverse fields observed in focused terahertz beams, New J. Phys. 14, 103049 (2012)

M. Beck, H. Schäfer, G. Klatt, J. Demsar, S. Winnerl, M. Helm, T. Dekorsy, Impulsive terahertz radiation with high electric fields from an amplifier-driven large-area photoconductive antenna, Optics Express 18, 9251-9257 (2010).

S. Winnerl, B. Zimmermann, F. Peter, H. Schneider, M. Helm, Terahertz Bessel-Gauss beams of radial and azimuthal polarization from microstructured photoconductive antennas, Optics Express 17, 1571-1576 (2009).

F. Peter, S. Winnerl, H. Schneider, M. Helm, K. Köhler, Terahertz emission from a large-area GaInAsN emitter, Appl. Phys. Lett. 93, 101102 (2008).

F. Peter, S. Winnerl, S. Nitsche, A. Dreyhaupt, H. Schneider, M. Helm,  Coherent terahertz detection with a large-area, non-resonant photoconductive THz antenna,  Appl. Phys. Lett. 91, 081109 (2007).

A. Dreyhaupt, S. Winnerl, M. Helm, T. Dekorsy, Optimum excitation conditions for the generation of high-electric-field THz radiation from an oscillator-driven photoconductive device, Optics Lett. 31, 1546 (2006).

A. Dreyhaupt, S. Winnerl, T. Dekorsy, M. Helm, High-intensity THz radiation from a microstructured large-area photoconductor, Appl. Phys. Lett. 86, 121114 (2005).