Optical limiters reverse saturable absorption

Reverse saturable absorption is an increase in the absorption coefficient of a material that is proportional to pump intensity. This phenomenon typically involves the population of a strongly absorbing excited state and is the basis of optical limiters or sensor protection elements. A variety of electronic and molecular reorientation processes can give rise to reverse saturable absorption many materials exhibit this phenomenon, including fuUerenes, phthalocyanine compounds (qv), and organometaUic complexes. 

One important process for organics that affords optical limiting behavior is reverse saturable absorption (RSA). If a substantial proportion of the... 

Reverse saturable absorption is another important nonlinear optical effect. Reverse saturable absorbers (RSAs) act as optical limiters by absorbing laser radiation. Therefore, they are particularly useful for laser protection, both civilian and military. Colorless infrared-absorbing RSAs which can absorb green laser radiation are especially important as they safeguard the eyes of pilots, tank commanders, etc. from enemy lasers [61],... 

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]. 

Although metallophthalocyanines have been studied in detail, there are few reports on optical limiting properties of porphyrins. Blau et showed reverse saturable absorption (RSA) by cobalt and zinc TPP complexes. Fei et reported RSA in Fe(TPP). Nonlinear excited state absorption in a series of metallotexaphyrin compounds (Figure 37)... 

OPTICAL LIMITING DEVICES BASED ON THE REVERSE SATURABLE ABSORPTION OF FULLERENES AND FULLERENE DERIVATIVES... 

The case (3 > 0, opposite to the previous one, can stem in nanocomposite media from reverse saturation of absorption (RSA), multi-photon absorption, or nonlinear scattering. It is of course of high interest for optical limiting applications. 

Concerning the optical properties it is remarkable that in the case of solution absorption spectra the saturation limit is bathochromically shifted using monoheptyl- instead of diheptylsubstituted PV products (s. Chapter 4.2.2), the emission behaviour is reverse. 

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