Spectroscopic characterization and performance of novel triplet state enhanced molecules for optical power limiting
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- Institutt for fysikk 
Finding molecules with good optical power limiting (OPL) performance is of greatimportance for the use in OPL filters made for protecting against harmful lasers used inan expanding set of technologies. In this thesis, the OPL performance and its underlyingmechanisms are investigated for three unstudied molecules of so called fluorenes, func-tionalized to have a triplet state central group. I abbreviate these molecules A, B and C.A previously studied molecule, PtOEP, is also investigated. The results are presented anddiscussed, in light of the five-level model. The OPL performance of A, B and C is mea-sured with an intensity scanning setup and the results indicate C as the best performer. Alarge difference in triplet state emission and a forbiddenS0T1transition separates C fromA and B. This makes triplet reverse saturable absorption (RSA) the OPL mechanism thatmakes C outperform the other molecules. The contribution of singlet RSA and two photonabsorption (TPA) to the OPL performance still have to be further characterized in termsof TPA, in order to obtain a full understanding of the underlying mechanisms. The OPLresults are also devalued by the appearance of nonlinear scattering, apparently caused bythe formation of small plasma bubbles in the solvent at high fluences.