Angular Dependent Light Emission From Planar Waveguides
JOURNAL OF APPLIED PHYSICS(2015)
摘要
We have investigated the angular dependence of amplified spontaneous emission (ASE) and laser emission from an asymmetric and free-standing polymer thin films doped with rhodamine 6G, which is transversely pumped by a pulsed Nd:YAG laser. A semi-leaky waveguide or quasi-waveguide structure has been developed by spin coating technique. In these waveguides, the light was confined by the film/air-film/glass substrate interfaces. At the film/substrate interface, a portion of light will reflect back into the film (guided mode) and the remaining refracted to the substrate resulting in cutoff modes. A blue-shift in ASE has been observed when the pump power was increased from 8 to 20 mW allowing a limited range of tuning of emission wavelength. To study the directionality of the ASE from the waveguide, we have measured the output intensity and FWHM of emission spectra as a function of viewing angle (theta) from the plane parallel to film. From the detailed examination of the output emission spectra, as +theta increases from 0 degrees there has been an initial decrease in output intensity, but at a particular angle approximate to 10 degrees an increase in output intensity was observed. This additional peak in output intensity as +theta is a clear indication of coexistence of the cutoff mode. We also present a compact solid-state laser based on leaky mode propagation from the dye-doped polymer free-standing film (similar to 50 mu m thickness) waveguide. The partial reflections from the broad lateral surfaces of the free-standing films provided the optical feedback for the laser emission with high directionality. For a pump power of 22 mW, an intense line with FWHM <0.2 nm was observed at 578 nm. (C) 2015 AIP Publishing LLC.
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关键词
angular dependent light emission
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