Third-harmonic generation and its applications in optical image processing† Canek Fuentes-Hernandez, a Gabriel Ramos-Ortiz,‡ b Shuo-Yen Tseng,x c Michael P. Gaj a and Bernard Kippelen * a Received 19th March 2009, Accepted 5th May 2009 First published as an Advance Article on the web 16th June 2009 DOI: 10.1039/b905561d We review potential applications of third-harmonic generation (THG) in polymer composites to implement optical image processing applications at the eye-safe and technologically relevant telecommunication bands. We discuss two examples, time-gated imaging through scattering media, and image recognition using Fourier-based techniques, where THG in a polymer composite offers significant advantages over typical holographic media, in that it produces signals that are non- degenerate in optical frequency and space, and allows the development of applications that are compatible with low-cost Si-based electronic components. 1. Introduction The continuous progress in fiber laser technology is bringing ultracompact lasers capable of producing ultrafast pulses at high repetition rates and high average powers to the market. A mature fiber laser technology along with the development of processable materials with large third-order nonlinear susceptibility, c (3) , 1–6 could bring on-chip 7,8 and free-space 4,5 all-optical signal pro- cessing (AOSP) one step closer to practical realization. In this context, the massive parallelism of optical systems continues to be attractive to develop applications that require computation- ally intensive operations. The problem of two-dimensional (2-D) image processing, which involves matrix convolutions and multiplications, is a good example where optical systems will continue to offer an advantage. When implemented with ultra- fast nonlinear optical (NLO) processes, computational rates exceeding 10 16 operations/second could be achieved 5 in relatively inexpensive and very compact optical correlators. 4,9,10 In comparison, occupying an area of around 560 m 2 , IBM Road- runner, the fastest supercomputer today, can perform 1.7  10 15 floating point operations per second. 11 Among the wide variety of c (3) processes that can be used to implement AOSP, third-harmonic generation (THG) is attrac- tive because it is an inherently ultrafast electronic process. However, THG is primarily being used as a tool for the NLO characterization of materials 12–14 and less as a potentially useful phenomena for the development of AOSP applications. To date, most THG applications have pertained to the characterization of ultrafast pulses through temporal autocorrelation 15,16 and by frequency-resolved optical gating (FROG). 17 Despite being less efficient than second-harmonic generation (SHG), the a Center for Organic Photonics and Electronics, School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA. E-mail: kippelen@ece.gatech.edu; Fax: +01 404 385 5170; Tel: +01 404 385 5163 b Optical Science Center, University of Arizona, Tucson, AZ, 85721, USA c Center for Organic Photonics and Electronics, School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA † This paper is part of a Journal of Materials Chemistry theme issue on organic non-linear optics. Guest editor: Seth Marder. ‡ Current address: Centro de Investigaciones en  Optica A.P. 1-948, 37000 Le on, Gto., M exico. x Current address: Department of Electro-Optical Engineering, National Cheng Kung University, No. 1 University Rd., Tainan, Taiwan. Canek Fuentes-Hernandez Canek Fuentes-Hernandez received his B.S. degree in Physics from the Universidad Nacional Aut  onoma de M exico in 1999 and his M.S. and Ph.D. degrees in Optical Sciences from the University of Arizona in 2003 and 2005. He is currently a research scientist at the Geor- gia Institute Technology. His research interests include non-linear optics of organic materials and metallic nano- structures, and micro-electronic devices. Gabriel Ramos-Ortiz Gabriel Ramos-Ortiz received his B.S. degree in Physics from the Universidad Nacional Aut  onoma de M exico in 1996, and his M.S. and Ph.D. degrees from the University of Arizona in 2000 and 2003. In 2004 he became a researcher at the Photonics Department at the Centro de Investigaciones en  Optica (CIO), in Le  on, M exico. His current research interests include nonlinear optical materials, spectroscopy and optical characterization of materials. 7394 | J. Mater. Chem., 2009, 19, 7394–7401 This journal is ª The Royal Society of Chemistry 2009 APPLICATION www.rsc.org/materials | Journal of Materials Chemistry