Space-time features of THz emission from optical rectification in sub-wavelength areas M. Peccianti 1,2 , S. P. Ho 1,4 , F. Buccheri 1,3 , M. Clerici 1 , A. Busacca 3 , T. Ozaki 1 , J. Ali 4 , R. Morandotti 1 1) INRS Énergie, Matériaux et Télécommunications, 1650 Blvd Lionel Boulet, Varennes (Québec), J3X 1S2 Canada Email: peccianti@emt.inrs.ca 2) IPCF-CNR, UOS Roma, University “Sapienza” P.le A. Moro 2, I-00185 Roma, Italy 3) DIEET, Viale delle Scienze, edif. n.9 - 90128 - University of Palermo, Italy 4) Nanophotonics Research Alliance, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia Abstract: We present our investigation on the THz space-time emission characteristic induced by the non-paraxial generation regime in highly localized THz generation via optical rectification on sub-wavelength areas. OCIS codes: (040.2235) Far infrared or terahertz; (050.6624) Subwavelength structure; (180.4243) Near-field microscopy 1. Introduction Thanks to the demonstrated advantage of terahertz (THz) spectroscopy in probing and recognizing compounds, THz microscopy has been attracting much interest for various potential applications in material characterization, in fields spanning from biology to security [1]. However, a strong limitation for microscopy purpose is the inherent low spatial resolution of THz imaging systems imposed by its long wavelength . For this reason, THz microscopy usually requires near-field techniques to overcome the diffraction limit [2-4]. Common approaches are spatial sampling with either sub-wavelength apertures [3] or sharp tips [4], which however exhibit a throughput that scales as r 6 , where r is the transverse resolution. An intriguing alternative has been recently explored, involving THz generation on a sub-wavelength area by focusing an optical pump on a nonlinear crystal. In this type of geometry, for excitation sizes smaller than the THz wavelength, the radiation throughput under a fixed excitation power from a thin, non-resonant, quadratic nonlinear material is inherently weakly dependent on the size of the optical excitation. This characteristic throughput is indeed the most important advantage of this design and indicates that this approach can be advantageous in microscopy when a sub-wavelength spatial resolution is required. In this case, microscopy is realized by placing the sample in the near-field region of the source. It has been experimentally determined that the throughput does not depend significantly on the resolution, down to dimensions below 30µm [5]. We investigate here on the spatiotemporal characteristics of the THz wave emitted in this generation geometry. Fig. 1: (a) Experimental set-up; (b) THz generation geometry; (c) Detected THz waveform and (d) associated spectrum. . OSA/ CLEO 2011 CThV2.pdf © Optical Society of America