Terahertz emission from lateral photo-Dember currents

Department of Physics and Center for Applied Photonics, University of Konstanz 78457, Germany.
Optics Express (Impact Factor: 3.49). 03/2010; 18(5):4939-47. DOI: 10.1364/OE.18.004939
Source: PubMed


The photo-Dember effect is a source of impulsive THz emission following femtosecond pulsed optical excitation. This emission results from the ultrafast spatial separation of electron-hole pairs in strong carrier gradients due to their different diffusion coefficients. The associated time dependent polarization is oriented perpendicular to the excited surface which is inaptly for efficient out coupling of THz radiation. We propose a scheme for generating strong carrier gradients parallel to the excited surface. The resulting photo-Dember currents are oriented in the same direction and emit THz radiation into the favorable direction perpendicular to the surface. This effect is demonstrated for GaAs and In(0.53)Ga(0.47)As. Surprisingly the photo-Dember THz emitters provide higher bandwidth than photoconductive emitters. Multiplexing of phase coherent photo-Dember currents by periodically tailoring the photoexcited spatial carrier distribution gives rise to a strongly enhanced THz emission, which reaches electric field amplitudes comparable to a high-efficiency externally biased photoconductive emitter.

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    • "In particular, over the roles of the metallic contact and the photo-excited charge density gradient . The work in [13] and [15] suggest that the metal layer is not required if a high gradient is present, whereas [16]–[18] suggest that the metal layer is crucial for emission. This has raised questions over the distribution of photo-current responsible for the lateral photo-Dember effect. "
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