Abstract
Unlike capillary resonance by Rayleigh (Proc. R. Soc. London29, 71 (1879)PRSLAZ0370-166210.1098/rspl.1879.0015) and optical resonance by Ashkin (Phys. Rev. Lett.38, 1351 (1977)PRLTAO0031-900710.1103/PhysRevLett.38.1351), acoustic resonance in fluid droplets has rarely been studied. Here we use droplets and optically excite and interrogate their acoustic resonances at a rate 1000 times faster than their capillary oscillation. We observe acoustical vibrations at 40&\#xA0;MHz that start at an optical threshold of 68&\#xA0;&\#x3BC;W. Their high optical quality factor suggests that droplets might also exhibit continuous-time optical nonlinearities and opto-capillary interactions. We believe that our work will enable photonic MEMS and droplet optomechanics in devices made strictly of liquid.
