Abstract-Active terahertz beam steering by photo-generated graded index gratings in thin semiconductor films

T. P. Steinbusch, H. K. Tyagi, M.C. Schaafsma, G. Georgiou, and J. Gómez Rivas  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-22-26559

Optics Express, Vol. 22, Issue 22, pp. 26559-26571 (2014)
http://dx.doi.org/10.1364/OE.22.026559

We demonstrate active beam steering of terahertz radiation using a photo-excited thin layer of gallium arsenide. A constant gradient of phase discontinuity along the interface is introduced by an spatially inhomogeneous density of free charge carriers that are photo-generated in the GaAs with an optical pump. The optical pump has been spatially modulated to form the shape of a planar blazed grating. The phase gradient leads to an asymmetry between the +1 and −1 transmission diffracted orders of more than a factor two. Optimization of the grating structure can lead to an asymmetry of more than one order of magnitude. Similar to metasurfaces made of plasmonic antennas, the photo-generated grating is a planar structure that can achieve large beam steering efficiency. Moreover, the photo-generation of such structures provides a platform for active THz beam steering.

© 2014 Optical Society of America

Abstract-Photo-generated THz antennas

G. Georgiou,

H. K. Tyagi,

P. Mulder,

G. J. Bauhuis,

J. J. Schermer

& J. Gómez Rivas

http://www.nature.com/srep/2014/140107/srep03584/full/srep03584.html#auth-5

Electromagnetic resonances in conducting structures give rise to the enhancement of local fields and extinction efficiencies. Conducting structures are conventionally fabricated with a fixed geometry that determines their resonant response. Here, we challenge this conventional approach by demonstrating the photo-generation of THz linear antennas on a flat semiconductor layer by the structured optical illumination through a spatial light modulator. Free charge carriers are photo-excited only on selected areas, which enables the realization of different conducting antennas on the same sample by simply changing the illumination pattern, thus without the need of physically structuring the sample. These results open a wide range of possibilities for the all-optical spatial control of resonances on surfaces and the concomitant control of THz extinction and local fields.