Dye-Doped, Polymer-Nanoparticle Gain Media for Tunable Solid-State Lasers
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Dye-Doped, Polymer-Nanoparticle Gain Media for Tunable Solid-State Lasers F. J. Duarte1 and R. O. James2 1 Eastman Kodak Company, R& D Laboratories, Rochester, New York 14650, U.S.A. 2 792 Oakridge Dr., Rochester, NY 14617, U.S.A. ABSTRACT Tunable laser action, in the visible spectrum, has been established using dye-doped, polymer-silica nanoparticle gain media. The silica nanoparticles, averaging about 12 nm in diameter, appear to be uniformly dispersed in the polymethyl methacrylate (PMMA) matrix, since the optical homogeneity of the gain medium is maintained. Using rhodamine 6G dye and 30% weight-by-weight (w/w) silica nanoparticles, laser action was established in the 567–603 nm range. At the peak wavelength (λ ~ 580 nm) laser conversion efficiency is ~63% at a beam divergence of 1.9 mrad (~1.3 times the diffraction limit). The new solid-state nanocomposite gain media also exhibits a reduction in | ∂n / ∂T | because the thermo-optic coefficient of silica is opposite in sign to that of the PMMA polymer-host component. INTRODUCTION Tunable solid-state organic lasers using dye-doped polymer gain media have been demonstrated to yield narrow-linewidth [1,2] and single longitudinal-mode (SLM) [3,4] emissions in compact multiple-prism grating oscillator configurations. An extensive review of recent developments of polymeric solid-state dye lasers has been recently reported by Costela et al. [5] The excellent optical homogeneity of these materials is one of the most important features of the dye-doped polymer gain media that allows attainment of TEM00 beam profiles and, consequently, the achievement of SLM emission [1,5,6]. Nevertheless, nearly all polymer gain media exhibit relatively high negative ∂n / ∂T values that impose limitations on the pulserepetition frequency (prf) and, ultimately, on the average power obtainable from these lasers [1,5-9]. One possible avenue available to improve the thermal properties of dye-doped, solid-state gain media is to use a composite organic inorganic matrix where the inorganic part is based on siliceous components (or other oxides with positive values for ∂n / ∂T ). Examples of such gain media are dye-doped, organically modified silicate (ORMOSIL) [10], tetraethoxysilane [1,11], and silica-polymer composites [12]. As far as narrow-linewidth and SLM-emission is concerned, traditional organic-inorganic composites are not well suited because they have been shown to exhibit internal refractive index inhomogeneities that produce a spatial decomposition of the emission [1,11,12]. This effect is due to internal interference and can be best illustrated by propagating a TEM00 laser beam through the material and observing the spatial profile of the beam a few meters from the sample. This problem with the beam quality of hybrid organic-inorganic nanocomposites has been noted in the most recent review by Costela et al. [5] who point out that it should be possible to "improve the homogeneity of the hybrid materials" through a range of chemical factors and properties of the gain media co
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