Browsing by Author "Tulek, A."
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Item Open Access Solid-state emissive BODIPY dyes with bulky substituents as spacers(American Chemical Society, 2009) Ozdemir, T.; Atilgan, S.; Kutuk, I.; Yildirim, L. T.; Tulek, A.; Bayındır, Mehmet; Akkaya, E. U.Bright fluorescence of the BODIPY dyes, just like most other fluorophores, is quenched in the solid state due to reabsorption and self-quenching. However, introduction of bulky ferf-butyl substituents on the meso-phenyl groups result in more spaced packing in the solid state, resulting in highly luminescent powders and films.Item Open Access Studies of polymer microring lasers subject to uniaxial stress(2007) Tulek, A.; Vardeny, Z.V.The emission spectra of microring lasers fabricated from π -conjugated polymer films casted on nylon microfibers with diameters in the range of 35-90 μm were studied upon application of uniaxial stress with strain up to ∼12%. The laser emission spectra substantially change with the applied stress, showing enhanced sensitivity to stress over changes induced in the fiber diameter alone. This is explained as due to the induced change in the polymer refractive index spectrum upon stress, causing an unexpected increase in the refractive index dispersion and, consequently, also in the effective refraction index for lasing at emission wavelengths. © 2007 American Institute of Physics.Item Open Access Ultralow threshold laser action from toroidal polymer microcavity(American Institute of Phycsics, 2009) Tulek, A.; Akbulut, D.; Bayındır, MehmetWe report laser action from a toroidal microcavity coated with π-conjugated polymer. An ultralow threshold value of ∼200 pJ/pulse is achieved by free space excitation in ambient conditions. This is the lowest threshold energy obtained in microtoroid lasers by free space excitation. The effective refractive index of the polymer, extracted from Fourier analysis of emission spectra, is 1.787, which is very close to measured value of 1.790 indicating that laser modes are located around the circumference of the cavity as whispering gallery resonances. © 2009 American Institute of Physics.Item Open Access Unidirectional laser emission from π-conjugated polymer microcavities with broken symmetry(2007) Tulek, A.; Vardeny, Z.V.We report unidirectional laser emission from π-conjugated polymer microcavities with broken symmetry geometries such as spiral and microdisk containing a "line defect," in comparison with plain microdisk cavity having isotropic emission. We found that the laser emission directionality contrast ratio is 8-10 and far field lateral divergence angle is 12°-15° for both broken symmetry geometries, with no significant increase in the laser threshold intensity. Fourier transform analysis of the laser emission spectra shows that unlike microdisks with line defect, the variation of light trajectories in the spiral microcavities leads to less defined laser modes. © 2007 American Institute of Physics.