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. 

Reverse saturable absorption, 17 457 Reverse sizing, in paper manufacture, 18 111... 

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

Fig. 1. Five-level model for reverse saturable absorption. (Adapted with permission from G. R. Allan, D. R. Labergerie, S. J. Rychnovsky, T. F. Bogess, A. L. Smirl, and L. Tutt, J. Phys. Chem. 1992,96,6313. Copyright 1992 American Chemical Society, Washington, DC.)...

Nonlinear optics is the interaction of laser radiation with a substance to produce new radiation which is altered in phase, frequency, and amplitude from the incident radiation. There are several types of nonlinear effects but the most important are second-order frequency doubling and reverse saturable absorption. 

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]. 

Lee I-YS, Suzuki H, Ito K, Yasuda Y (2004) Surface-enhanced fluorescence and reverse saturable absorption on silver nanoparticles. J Phys Chem B 108 19368-19372... 

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)... 

The nonlinear material is critical to the operation of a limiter. Several different nonlinear effects can be used in the nonlinear element to provide a limiting function. Nonlinear absorption, where the material absorbance increases with the intensity of the incident light, is the most useful mechanism to remove light from the transmitted beam. A large number of organic and organometallic materials have been reported to exhibit an intensity dependent increase in absorption, sometimes called a reverse saturable absorption. The most effective are phthalocyanines (2, 3,4, 5) and porphyrins. (6,7)... 

Y.B. Band, J. Chem. Phys.,"Reverse Saturable Absorption of Short Polarized Light Pulses", in press. 

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

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