Nonlinear Mie scattering: electrostrictive coupling of light to droplet acoustic modes

Effect of crystalline family and orientation on stimulated Brillouin scattering in whispering-gallery mode resonators

Ultra-high Q whispering-gallery mode resonators pumped by a continuous-wave laser are known to enhance stimulated Brillouin scattering when optimal resonance and phase-matching conditions are met. In crystalline resonators, this process depends critically on the crystal orientation and family, which impose the elastic constants defining the velocity of the acoustic waves. In this article, we investigate the effect of crystalline orientation and family on this velocity which is proportional to the Brillouin frequency down-shift. In particular, the study is based on the development of a model and numerical simulations of acoustic wave velocities that propagate along the periphery of four fluoride crystals, namely calcium, magnesium, lithium and barium fluoride. We find that depending on the crystal and its orientation, the frequency excursion around the Brillouin offset can vary from few tens of kHz to more than a GHz.

Brillouin lasing with a CaF2 whispering gallery mode resonator

Stimulated Brillouin scattering with both pump and Stokes beams in resonance with whispering gallery modes of an ultrahigh Q calcium fluoride resonator is demonstrated for the first time. The resonator is pumped with 1064 nm light and has 3 muW Brillouin lasing threshold. The scattering is observed due to the unique morphology of the resonator reducing the phase mismatch between the optical modes and the hypersound wave.

Different temporal behavior for the forward- and backward-circulating radiation within a microdroplet

Spatially resolved nonlinear scattering of a train of picosecond pulses from ethanol microdroplets is investigated. Different time behavior is observed for light with the same and the opposite sense of circulation as the input-coupled light. The forward-circulating light exhibits a smooth, delayed pulse-to-pulse growth, attributed to increased input coupling with time induced by the laser pulses. The backward-circulating light has an irregular time behavior, attributed to near-backward stimulated Brillouin scattering. Increased scattering as a result of CO(2) (compared with He) dissolved gas is demonstrated by an intensity decrease of the spatially precessed radiation on a cavity resonance.

Absorption effects on microdroplet resonant emission structure

The effect of absorption on microdroplet resonance emission line intensities was studied in 15-microm-diameter Rhodamine 6G/ethanol solution droplets. Absorption was controlled by varying the concentration of the additive nigrosin. Spectrally integrated intensities of resonant features are found to be proportional to a droplet cavity mode efficiency Q(a)/(Q(a)+Q(o)) expressed in terms of cavity output coupling and absorption factors Q(o) and Q(a), respectively. These Q's are determined from linewidths calculated from Lorenz-Mie theory by using combinations of the real and complex indices of refraction. An experimental upper limit of Q for first-order modes was determined to be 10(8) from the data.