Resonance of surface waves on spheres

Rayleigh and whispering gallery waves have been excited in a steel sphere of 20 nm diameter by a YAG (yttrium aluminum garnet) laser beam whose intensity was modulated by a Bragg cell. The normal component of the vibration was measured by a sensitive interferometric probe. Resonances of both modes have been observed in the range 100-1500 kHz. As predicted by the analysis of the mechanical displacement distribution on the surface, the Rayleigh wave resonances gave larger probe signals than the whispering gallery waves. The Q-factors were about 10 ⁴. This observation technique of spherical resonances does not require any mechanical contact. It is concluded that this advantage could be used to evaluate the mechanical characteristics of free balls