Position-resolved Raman spectra from a laser-trapped single airborne chemical droplet

It could be very useful to detect and monitor the molecules and molecular reactions located at different positions within a microsized particle as they respond to various micro-local environments. In this Letter, a particular optical trap using two focusing counterpropagating hollow beams was able to stably trap both absorbing and nonabsorbing particles in air for lengthy observation. A technique that can measure the Raman spectra from different submicrometer positions of a laser-trapped single airborne particle was developed. Spontaneous and stimulated Raman scattering spectra originating from different positions of a diethyl phthalate droplet were recorded, and the strong Raman scattering signals are the result of cavity-enhanced effects and the localized strong light illumination.