Excimer

About: Excimer is a research topic. Over the lifetime, 3725 publications have been published within this topic receiving 75104 citations.

Excimer laser calibration system

Abstract: BACKGROUND Excimer laser photoablation for refractive and therapeutic keratectomies has been demonstrated to be feasible and practicable. However, corneal laser ablations are not without problems, including the delivery and maintenance of a homogeneous beam. We have developed an excimer laser calibration system capable of characterizing a laser ablation profile. METHODS Beam homogeneity is determined by the analysis of a polymethylmethacrylate (PMMA)-based thin-film using video capture and image processing. The ablation profile is presented as a color-coded map. Interpolation of excimer calibration system analysis provides a three-dimensional representation of elevation profiles that correlates with two-dimensional scanning profilometry. Excimer calibration analysis was performed before treating a monkey undergoing phototherapeutic keratectomy and two human subjects undergoing myopic spherocylindrical photorefractive keratectomy. Excimer calibration analysis was performed before and after laser refurbishing. RESULTS Laser ablation profiles in PMMA are resolved by the excimer calibration system to .006 microns/pulse. Correlations with ablative patterns in a monkey cornea were demonstrated with preoperative and postoperative keratometry using corneal topography, and two human subjects using video-keratography. Excimer calibration analysis predicted a central-steep-island ablative pattern with the VISX Twenty/Twenty laser, which was confirmed by corneal topography immediately postoperatively and at 1 week after reepithelialization in the monkey. Predicted central steep islands in the two human subjects were confirmed by video-keratography at 1 week and at 1 month. Subsequent technical refurbishing of the laser resulted in a beam with an overall increased ablation rate measured as microns/pulse with a donut ablation profile. A patient treated after repair of the laser electrodes demonstrated no central island. CONCLUSIONS This excimer laser calibration system can precisely detect laser-beam ablation profiles. The calibration system correctly predicted central islands after excimer photoablation in a treated monkey cornea and in two treated human subjects. Detection of excimer-laser-beam ablation profiles may be useful for precise calibration of excimer lasers before human photorefractive and therapeutic surgery.

Balancing Charge Transfer and Frenkel Exciton Coupling Leads to Excimer Formation in Molecular Dimers: Implications for Singlet Fission.

Abstract: Photoexcitation of molecular chromophore aggregates can form excimer states that play a significant role in photophysical processes such as charge and energy transfer as well as singlet fission. An excimer state is commonly defined as a superposition of Frenkel exciton and charge transfer states. In this work, we investigate the dynamics of excimer formation and decay in π-stacked 9,10-bis(phenylethynyl)anthracene (BPEA) covalent dimers appended to a xanthene spacer, where the electronic coupling between the two BPEA molecules is adjusted by changing their longitudinal molecular slip distances. Using exciton coupling calculations, we quantify the relative contributions of Frenkel excitons and charge transfer states and find that there is an upper and lower threshold of the charge transfer contribution for efficient excimer formation to occur. Knowing these thresholds can aid the design of molecular aggregates that optimize singlet fission.

Excimer and exciplex formation in a pair of bright phosphorescent isomers constructed from Cu3(pyrazolate)3 and Cu3I3 coordination luminophores

Abstract: Reported herein are a pair of supramolecular pseudo-isomers, namely, (Cu3I3)(Cu3L3)2·H2O (1) and (Cu3I3)(Cu3L3)2 (2) (L = 3-(4-pyridyl)-5-isobutyl-pyrazolate), both of which incorporate Cu3Pz3 (Pz = pyrazolate) and Cu3I3 clusters as luminophores. The two complexes show distinct yellow (570 nm) and orange (638 nm) emissions, which are ascribed to the formation of the excimer and exciplex involving the same or different copper(I)-cluster-based luminophores.

Excimer-like emission from linear π-conjugated poly(pyridine-2,5-diyl)

Abstract: π-Conjugated poly(pyridine-2,5-diyl) and poly(2,2′-bipyridine-5,5′-diyl) give rise to fluorescence in formic acid solutions, in the solid state (film), and in an adduct with poly(vinyl alcohol); the fluorescence in the solid state, in the adduct with poly(vinyl alcohol), and in the formic acid solution with relatively high concentration of the polymer is interpreted by assuming excimer formation.