Cavity Enhanced Raman Spectroscopy of Optically Trapped Aerosols

Small transparent particles can be suspended in air using a laser to create an optical trap. It has been observed that the intensity of the laser affects the position of trapped aqueous aerosol droplets. The stable positions that the droplet varies between are caused by a resonance of the light from the trapping beam on the surface of the droplet, called Whispering Gallery Modes. When this resonance occurs, forces acting on the droplet cause it to move. To determine an understanding for this behavior, the droplet’s position is correlated to the Raman scattered light. The spectrum of light scattered from the droplet’s surface produces peaks in intensity, known as Cavity Enhanced Raman Spectroscopy. Certain properties of the droplet, such as the diameter and refractive index, can be harvested by analyzing the location and spacing of the peaks. This analysis gives precise measurements of the droplet’s radius, which can be used to determine if a resonance occurs when the droplet moves.