Forward and backward stimulated Brillouin scattering in aqueous suspension of SiO2 spherical nanoparticles

Both backward and forward directed Stimulated Brillouin Light Scattering (SBLS) are observed in an aqueous suspension of SiO2 nanoparticles with diameters of 100 and 200 nm by using for excitation a second harmonic (λ = 532 nm, 10 ns) of a single (∼0.005 cm−1) mode YAG:Nd3+ laser. Both backward and forward directed SBLS are characterized by a low beam divergence and typically for a water Stokes shift of ≈0.25 cm−1. The microscopic explanation of forward directed SBLS in an aqueous suspension of SiO2 spherical nanoparticles is proposed.