We show that time-independent scattering coefficients calculated from the standard extrapolation of Mie theory to the gain regime have physical meaning up to the laser threshold. The theoretical width of a resonance decreases linearly with increasing gain and becomes zero at the laser threshold. We performed experiments on dielectric microspheres with gain, trapped with optical tweezers. The width of the mode was measured to narrow as a function of the gain up to the lasing threshold, confirming both the validity of the extrapolation of Mie theory to the gain regime below threshold and our interpretation of its point of divergence as the laser threshold.
© 2006 Optical Society of America
Lasers and Laser Optics
Original Manuscript: February 1, 2006
Manuscript Accepted: February 20, 2006
Vol. 1, Iss. 6 Virtual Journal for Biomedical Optics
Karen L. van der Molen, Peter Zijlstra, Ad Lagendijk, and Allard P. Mosk, "Laser threshold of Mie resonances," Opt. Lett. 31, 1432-1434 (2006)