The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the functi...

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation.

Within the scope of nonlinear optics, optical power limiting (OPL) materials are commonly regarded as an important class of compounds which can protect the delicate optical sensors or human eyes from sudden exposure to damaging intense laser beams. Recent efforts have been devoted to developing organometallic acetylide complexes, dendrimers and polymers as high performance OPL materials of the next generation which can favorably optimize the optical limiting/transparency trade-off issue. These metallated materials offer a new avenue towards a new family of highly transparent homo- and heterometallic optical limiters with good solution processability which outperform those of current state-of-the-art visible-light-absorbing competitors such as fullerenes, metalloporphyrins and metallophthalocyanines. This critical review aims to provide a detailed account on the recent advances of these novel OPL chromophores. Their OPL activity was shown to depend strongly on the electronic characters of the aryleneethynylene ligand and transition metal moieties as well as the conjugation chain length of the compounds. Strategies including copolymerization with other transition metals, change of structural geometry, use of a dendritic platform and variation of the type and content of transition metal ions would strongly govern their photophysical behavior and improve the resulting OPL responses. Special emphasis is placed on the structure–OPL response relationships of these organometallic acetylide materials. The research endeavors for realizing practical OPL devices based on these materials have also been presented. This article concludes with perspectives on the current status of the field, as well as opportunities that lie just beyond its frontier (106 references).

Organometallic acetylides of PtII, AuI and HgII as new generation optical power limiting materials

Reverse saturable absorption in tetraphenylporphyrins

We provide an in-depth treatment of the various mechanisms by which an incident light beam can produce an intensity- or flux-dependent change in the refractive index and absorption coefficient of different materials. Whenever possible, the mechanisms are initially traced to single-atom and -molecule effects in order to provide physical understanding. Representative values are given for the various mechanisms. Nine different mechanisms are discussed, starting with the Kerr effect due to atoms and/or molecules with discrete states, including organic materials such as molecules and conjugated polymers. Simplified two and/or three-level models provide useful information, and these are summarized. The nonlinear optics of semiconductors is reviewed for both bulk and quantum-confined semiconductors, focusing on the most common types II–VI and III–V. Also discussed in some detail are the different nonlinear mechanisms that occur in liquid crystals and photorefractive media. Additional nonlinear material systems and mechanisms such as glasses, molecular reorientation of single molecules, the electrostrictive effect, the nuclear effect (vibrational contributions), cascading, and the ever-present thermal effects are quantified, and representative tables of values are given.

Nonlinear refraction and absorption: mechanisms and magnitudes

We demonstrate optical limiting for the C60 fullerene in polymethyl methacrylate (PMMA) as a solid polymer host. It is shown that the optical-limiting behavior is consistent with excited-state absorption (reverse saturable absorption) as a mechanism. We suggest that a higher threshold for optical limiting compared with that of C60 in toluene is due to nonlinear scattering for the liquid. The performance of C60 in PMMA is compared with that in chloroaluminum phthalocyanine, N-methylthioacridone, King’s complex, and ruthenium King’s complex in PMMA. Optical damage thresholds are reported.

Optical limiting with C 60 in polymethyl methacrylate

A review of spectroscopic properties of complex molecules is presented and used to show that a simple two-level scheme is inadequate to describe the optical bleaching of dye molecules. Experimental data are reported for the transmission of intense ruby laser radiation by several types of dyes. Rate equation analyses are carried out using steady-state solutions and iterative computer solutions; calculated bleaching curves are compared with our data for cryptocyanine. On these bases, we show that, in general, the optical bleaching process involves the removal of ground-state molecules to other states having smaller absorption cross sections at the exciting frequency, and that recovery of absorption at this frequency is characterized by a complex relaxation mechanism.

Nonlinear absorption of light: Optical saturation of electronic transitions in organic molecules with high intensity laser radiation

A simple analytical model is presented to describe the delay τ c between flashlamp initiation and laser-pulse onset in the flash-photolysis HF chemical laser. The predictions of the model agree well with experiments concerning the functional dependence of τ c on pressure, flashlamp intensity, optical cavity loss, and the absolute magnitude of τ c . This detailed agreement between theory and laser performance has not been achieved in previous chemical laser work. The pulse-delay measurements demonstrate the presence of complete vibrational inversion at the time of laser-pulse initiation. In the Appendixes, the fractional photodissociation of MoF 6 is calculated for the experimental geometry used, the effects of flashlamp heating are considered, and a general expression for the temperature dependence of HF laser gain is derived and plotted. A complete bibliography of laser transitions in HF and DF is included.

L. Hess

Papers

Nonlinear absorption of light: Optical saturation of electronic transitions in organic molecules with high intensity laser radiation

Study of the HF chemical laser by pulse-delay measurements

A chemically reversible photodissociative laser system

DF-CO 2 chemical transfer laser

Enhanced initiation and high pressure operation of the HF chemical laser