Species identification of multicomponent microdroplets by seeding stimulated Raman scattering

Abstract

External seeding of stimulated Raman scattering (SRS) is applied to enhance the signal from the minority species in multicomponent microdroplets. However, to avoid complications in discriminating the elastically scattered seed laser from the minority-species SRS, we utilize the fact that the seeded SRS band of the minority species (at νmin) can efficiently pump SRS of the majority species (at νmaj). The resultant signal appears at a shift of νmin+maj, which is easily discriminated from the elastic scatter of the seed laser at a shift of νmin. Our method results in a threefold reduction in the minimum detectable concentration of toluene in toluene/ethanol droplets as compared with conventional SRS.