A pump-probe two-photon-excited fluorescence technique deciphers in space and time the propagation of ballistic wave packets sustained by whispering-gallery modes (WGMs) in a spiral-shaped microcavity. Diffraction on the spiral discontinuity does not prevent the WGMs from closing. The resultant average Q of the resonator is 3×10^4 ± 50%. Experimental results are compared with numerical simulations, providing evidence of a new contribution to output coupling: Part of the WGM evanescent wave is reflected at the spiral notch and leads to a propagating wave at an angle that matches the previously observed laser emission direction in 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran-doped poly(methyl methacrylate) and InGaN spiral lasers.
© 2005 Optical Society of America
(060.5530) Fiber optics and optical communications : Pulse propagation and temporal solitons
(120.3180) Instrumentation, measurement, and metrology : Interferometry
(140.4780) Lasers and laser optics : Optical resonators
(170.6920) Medical optics and biotechnology : Time-resolved imaging
(320.2250) Ultrafast optics : Femtosecond phenomena
F. Courvoisier, V. Boutou, J. P. Wolf, R. K. Chang, and J. Zyss, "Deciphering output coupling mechanisms in spiral microcavities with femtosecond light bullets," Opt. Lett. 30, 738-740 (2005)