Optical limiters nonlinear material

Materials are also classified according to a particular phenomenon being considered. AppHcations exploiting off-resonance optical nonlinearities include electrooptic modulation, frequency generation, optical parametric oscillation, and optical self-focusing. AppHcations exploiting resonant optical nonlinearities include sensor protection and optical limiting, optical memory appHcations, etc. Because different appHcations have different transparency requirements, distinction between resonant and off-resonance phenomena are thus appHcation specific and somewhat arbitrary. 

Nonlinear optical organic materials such as porphyrins, dyes, and phthalocyanines provide optical limiting properties for photonic devices to control light frequency and intensity in a predictable manner. The optical limit of CNTs composites is saturated at CNTs exceeding 3.8wt% relative to the polymer mass (Chen et al., 2002). Polymer/ CNT composites could also be used to protect human eyes, for example, optical elements, optical sensors, and optical switching (Cao et al., 2002). 

Asher S, Chang S-Y, Tse A, Liu L, Pan G, Wu Z, Li P. Optically nonlinear crystalline colloidal self assembled submicron periodic structures for optical limiters. Material Research Society Symposium Proceedings 1995, 374, 305-310. 

A series of solution-processible and tractable polymetallaynes of Pt and their mixed-metal analogues were demonstrated to be excellent OPL materials to nanosecond laser pulses at 532 nm, with optimized optical transparency/ nonlinearity trade-offs. The optical-limiting behavior of selected platinum(II) polyynes was investigated by the Z-scan technique. Polyynes 19, 21, 22, 27, 29,... 

Optical limiting is by definition an optical nonlinear phenomenon that results in an increase of the optical absorption as the incident irradiation increases. Due to the fact that the triplet photoexcited state of C60 can absorb light more efficiently than its ground state, as the intensity of the incoming irradiation increases the intensity of the transmitted irradiation does not increase linearly [263,264]. The latter, together with both the extension of optical absorption to the near-IR of mono-organofullerene adducts and the resulting reduction of symmetry of the functionalized materials, as compared with the intact C60, has allowed several... 

The most widely employed material characterization techniques in third-order nonlinear optics are third-harmonic generation (THG) [21], degenerate four wave-mixing (DFWM) [22], Z-scan [6], and optical limiting by direct two-photon absorption (TPA) and fluorescence spectroscopy induced by TPA [23]. All of them will be discussed in the following. Further measurement techniques such as electric-field induced second-harmonic generation (EFISH) [24], optical Kerr... 

There is a close relation between NLO and optical limiting (OL) properties. The main mechanisms to achieve OL are nonlinear absorption (NLA) and nonlinear refraction (NLR), but other effects such as nonlinear scattering can also contribute to OL. Materials with a positive NLA coefficient exhibit reverse saturable absorption (RSA), causing a decrease in transmittance at high intensity levels, and so operate as optical limiters [14]. 

High quantum yield photochemical reactions of condensed-phase species may become useful for future optical applications such as molecular switches, optical limiters, and read-write data storage media. Toward these ends, much research has been conducted on novel nonlinear chemical-based materials such as conducting polymers and metal-organic species. Monitoring the early time-dependent processes of these photochemical reactions is key to understanding the fundamental mechanisms and rates that control the outcome of these reactions, and this could lead to improved speed and efficiencies of devices. 

Both TCSPC and frequency-domain fluorimetry are limited in time resolution by the response of available detectors, typically >25 ps. For cases in which higher time resolution is needed, fluorescence up-conversion can be used (22). This technique uses short laser pulses (usually sub-picosecond) both to excite the sample and to resolve the fluorescence decay. Fluorescence collected from the sample is directed through a material with nonlinear optical properties. A portion of the laser pulse is used to gate the fluorescence by sum frequency generation. The fluorescence is up-converted to the sum frequency only when the gate pulse is present in the nonlinear material. The up-converted signal is detected. The resolution of the experiment therefore depends only on the laser pulse widths and not on the response time of the detectors. As a result, fluorescence can be resolved on the 100-fs time scale. For a recent application of fluorescence up-conversion to proteins, see Reference 23. 

For symmetry reasons, the first macroscopic nonlinear coefficient is zero in unordered polymer materials. On the other hand, azo-dye polymers can exhibit very large values, which is interesting for applications in optical limiting and optical switching devices. We will consider the relationship between microscopic and macroscopic third-order susceptibilities. The most general equation for this relationship can be written as ... 

Tlie usual experimental techniques developed to study the optical Kerr effect in materials have already been described in a preceding chapter of this book. We only mention here the methods which have especially been used for nanocomposite materials as colloidal solutions or thin films Degenerate four-wave mixing (DFWM) and optical phase conjugation, which provide the modulus of x only and may be completed by Interferometry techniques to get its phase as well, optical limiting, optical Kerr shutter, and z-scan, which is probably the most common technique used in recent years due to its ability to provide simultaneously the nonlinear refraction and absorption coefficients of the same sample point [118],... 

Fullerene has important properties as a nonlinear material, particularly as an optical limiting material with applications in device fabrication. The poor solubility of this material and the processing difficulties associated with it severely limit its direct application, however. One possibility of overcoming these disadvantages involves binding polymers on to Ceo to obtain fullerene-based polymeric materials with peculiar physical and/or chemical properties and good processability. 

Nanostructured Polymeric Nonlinear Photonic Materials for Optical Limiting... 

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