This special volume contains the proceedings of the 9th Epioptics Workshop, held at the Ettore Majorana Foundation and Centre for Scientific Culture, Erice, Sicily, from July 20 to 26, 2006. The workshop was the 9th in the Epioptics series and the 39th of the International School of Solid State Physics. The workshop was aimed at assessing the capabilities of state-of-the-art optical techniques in elucidating the fundamental electronic and structural properties of semiconductor and metal surfaces, interfaces, thin layers, and layer structures, and at assessing the usefulness of these techniques for optimization of high-quality multilayer samples through feedback control during materials growth and processing. Particular emphasis is dedicated to the theory of non-linear optics and to dynamical processes through the use of pump-probe techniques together with the search for new optical sources. Some new applications of scanning probe microscopy to material science and biological samples, dried and in vivo, with the use of different laser sources are also presented. Sample Chapter(s). Longitudinal Gauge Theory of Surface Second Harmonic Generation (966 KB). Contents: Longitudinal Gauge Theory of Surface Second Harmonic Generation (B S Mendoza); Excited State Properties Calculations: From 0 to 3 Dimensional Systems (M Marsili et al.); High Spatial Resolution Raman Scattering for Nano-structures (E Speiser et al.); Vibrational Properties and the Miniband Effect in InGaAs/InP Superlattices (A D Rodrigues et al.); Electronic and Optical Properties of ZnO Between 3 and 32 eV (M Rakel et al.); Order and Clusters in Model Membranes: Detection and Characterization by Infrared Scanning Near-Field Microscopy (J Generosi et al.); Chemical and Magnetic Properties of NiO Thin Films Epitaxially Grown on Fe(001) (A Brambilla); Probing the Dispersion of Surface Phonons by Light Scattering (G Benedek & J P Toennies); and other papers. Readership: Researchers as well as graduate and postgraduate students in applied physics, specifically semiconductors and related areas, electron microscopy and condensed matter physics.