Abstract-Geometric phase shaping of terahertz vortex beams

Amalya Minasyan, Clément Trovato, Jérôme Degert, Eric Freysz, Etienne Brasselet, and Emmanuel Abraham

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-1-41

We propose a topological beam-shaping strategy of terahertz (THz) beams using geometric phase elements made of space-variant birefringent slabs. Quasi-monochromatic THz vortex beams are produced and characterized both in amplitude and phase from the reconstructed real-time two-dimensional imaging of the electric field. Nonseparable superpositions of such vortex beams are also obtained and characterized by two-dimensional polarimetric analysis. These results emphasize the versatility of the spin-orbit electromagnetic toolbox to prepare on-demand structured light endowed with polarization-controlled orbital angular momentum content in the THz domain, which should find many uses in future THz technologies.

© 2016 Optical Society of America

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Abstract-Simple and distortion-free optical sampling of terahertz pulses via heterodyne detection schemes

Jérôme Degert, Marion Cornet, Emmanuel Abraham, and Eric Freysz
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-10-2045

We present and demonstrate experimentally two simple and distortion-free methods to sample terahertz pulse in zinc-blende-type crystals like ZnTe or GaP. They are based on an optical heterodyne detection scheme which makes it possible to measure the terahertz field by detecting the optical probe beam or its second harmonic. Both are compared to conventional electro-optic sampling and give results in good agreement with the latter.

© 2016 Optical Society of America

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Abstract-Development of a wavefront sensor for terahertz pulses

Emmanuel Abraham, Harsono Cahyadi, Mathilde Brossard, Jérôme Degert, Eric Freysz, and Takeshi Yasui
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-5-5203

Wavefront characterization of terahertz pulses is essential to optimize far-field intensity distribution of time-domain (imaging) spectrometers or increase the peak power of intense terahertz sources. In this paper, we report on the wavefront measurement of terahertz pulses using a Hartmann sensor associated with a 2D electro-optic imaging system composed of a ZnTe crystal and a CMOS camera. We quantitatively determined the deformations of planar and converging spherical wavefronts using the modal Zernike reconstruction least-squares method. Associated with deformable mirrors, the sensor will also open the route to terahertz adaptive optics.

© 2016 Optical Society of America

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Abstract-Tuning photoinduced terahertz conductivity in monolayer graphene: Optical-pump terahertz-probe spectroscopy

Srabani Kar, Dipti R. Mohapatra, Eric Freysz, and A. K. Sood

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.165420

Optical-pump terahertz-probe differential transmission measurements of as-prepared single layer graphene (AG) (unintentionally hole doped with Fermi energy EF at ∼−180meV), nitrogen doping compensated graphene (NDG) with EF∼−10 meV, and thermally annealed doped graphene (TAG) are examined quantitatively to understand the opposite signs of photoinduced dynamic terahertz conductivity Δσ. It is negative for AG and TAG but positive for NDG. We show that the recently proposed mechanism of multiple generations of secondary hot carriers due to Coulomb interaction of photoexcited carriers with the existing carriers together with the intraband scattering can explain the change of photoinduced conductivity sign and its magnitude. We give a quantitative estimate of Δσ in terms of controlling parameters—the Fermi energy EF and momentum relaxation time τ. Furthermore, the cooling of photoexcited carriers is analyzed using a supercollision model which involves a defect mediated collision of the hot carriers with the acoustic phonons, thus giving an estimate of the deformation potential.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.165420

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• Published 16 October 2014
• Received 11 June 2014
• Revised 16 August 2014

©2014 American Physical Society

Abstract-Terahertz-field-induced second harmonic generation through Pockels effect in zinc telluride crystal

Marion Cornet, Jérôme Degert, Emmanuel Abraham, and Eric Freysz  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-20-5921

Optics Letters, Vol. 39, Issue 20, pp. 5921-5924 (2014)
http://dx.doi.org/10.1364/OL.39.005921

We report on the second harmonic generation (SHG) of a near-infrared pulse in a zinc telluride crystal through the Pockels effect induced by an intense terahertz pulse. The temporal and angular behaviors of the SHG have been measured and agree well with theoretical predictions. This phenomenon, so far overlooked, makes it possible to generate second harmonic through cascading of two second-order nonlinear phenomena in the near-infrared and terahertz ranges. We also show how this cascading process can be used to sample terahertz pulses.

© 2014 Optical Society of America