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Mie theory: Resonances in spheres with gain |
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Optical resonances occur not only in microspheres made of loseless or lossy materials. In these materials, the imaginary term, m", of the complex refractive index is respectively equal to or greater than 0. In materials providing optical gain, that term is positive. van der Molen et al (2006) investigated experimentally and theoretically the behavior of optical resonances for microspheres made of a material with gain. They used ~10 µm diam polystyrene microspheres doped with 2% fluorescent dye emitting in a wavelength range of 480 to 540 nm (m' = 1.583, m" = 1.5e-5) and excited with a 470-nm laser generating ~3 ns pulses with an energy (at the microsphere) on the order of 100 nJ.
van der Molen et al found that the width of a resonance peak decreases linearly with increasing gain until 0 at the laser thershold, defined as the pump power at which the gain of a laser cavity (here the microsphere) begins to exceed the loss. They point out that the laser threshold places a natural limit on the applicability of an extension of Mie theory to include particle materials with gain (for example, Kerker et al 1980).
| CITATION: Jonasz M. 2006. Mie theory: Resonances in spheres with gain (www.tpdsci.com/Tpc/MieOptResGain.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 15-May-2006 Modified: 22-May-2006 Reviewed: 22-May-2006 |
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