Zayıf ve güçlü kuplaj rejimlerinde kavite-modifiye floresans

The modulation of fluorescence in optical microcavities provides a powerful route for engineering light–matter interactions, with applications in sensing, lasing, and photonic devices. Fabry–Pérot (FP) cavities, composed of planar metallic mirrors enclosing an active medium, enable controlled tuning of emission dynamics across weak and strong coupling regimes. In the weak coupling regimes, cavities reshape radiative decay rates via the Purcell effect. In contrast, in the strong coupling regime, coherent exciton–photon interactions produce vacuum Rabi splitting and exciton–polariton formation. While strong coupling has been extensively demonstrated using narrow-linewidth dyes, such as rhodamines, the behavior of broadband emitters, like fluorescein, under cavity confinement remains poorly understood. This thesis presents a systematic experimental investigation of fluorescein-doped poly(methyl-methacrylate) (PMMA) thin films embedded in FP microcavities. Two concentrations of fluorescein were used, low (20 µg/mL) and high (60 mg/mL), across multiple film thicknesses defined by spin coating speeds (1000–5000 rpm). The low-concentration series comprised films with the thickness of 486, 349, 291, 253, and 240 nm, while the high-concentration series comprised cavities with the film thickness of 669, 476, 380, 334, and 307 nm. Optical properties were characterized by spectroscopic ellipsometry, UV–Vis spectroscopy, steady-state fluorescence, and angle-resolved reflectance. Transfer matrix method (TMM) simulations, incorporating measured refractive indices and extinction coefficients, validated experimental results. At low dye concentrations, cavity confinement primarily induced significant spectral reshaping without mode splitting, consistent with the weak coupling regime. In contrast, high-concentration samples exhibited clear signatures of strong exciton–photon coupling. Angle-resolved ellipsometry revealed secondary loops in the complex-plane ρ trajectories, while reflectance dispersion maps displayed anticrossing behavior when cavity modes overlapped with the fluorescein excitonic transition near 467 nm. Angle-resolved dispersion was fitted with a three-coupled-oscillator model, yielding vacuum Rabi splittings ranging from 34.8 nm to 48.5 nm, and the dispersion shows back-bending of the cavity mode near 467 nm, consistent with exciton–photon coupling. These results demonstrate that, despite its broad linewidth, fluorescein can achieve strong coupling under optimized conditions of high concentration and tuned cavity thickness. The work provides a quantitative framework for extending cavity–emitter studies to broadband dyes and offers design principles for future cavity-enhanced light sources, lasers, and fluorescence-based sensors.