Diagnostic and photoinduced nonlinear effects in highly conjugated organic compounds

Nonlinear optics has been the subject of intensive research because of its wide application in the field of photonics, such as optical signal processing, broadband optical communications, integrated optics, optical sensing, optical poling, optical limiting, optical computing, etc. A common problem in laser technology is the protection of the human eye and of optical sensors from the damaging effects of high-energy light. Passive optical limiters can be the solution of this kind of problem. Therefore, optical materials with large coefficients of TPA and nonlinear refraction are of prime importance in optical limiting applications. Recently, the C₆₀-TTF compounds have attracted much attention because of their three-dimensional π-electron conjugated systems which makes them promising as new limiting materials. Two-photon absorption, second harmonic generation (SHG), detection of phase transitions using photoinduced nonlinear effects and an illustration of a new system for optical recording and erasing of holograms under weak laser illumination are discussed.