Imaging in optical micromanipulation using two-photon excitation

Recent studies have realized optical micromanipulation of extended two- and three-dimensional structures and optical binding. In many recent experiments the optical interaction between particles and their light scattering has played a key role. We use fluorescein dye within the sample medium and a femtosecond laser for optical micromanipulation. By the process of two-photon excitation we can directly observe how the light behaves during refraction and reflection within a sample of optically guided microspheres. We directly visualize the reconstruction of the Bessel light beam by excitation of two-photon fluorescence when used as an optical guide for microscopic particles dispersed within this dyed medium. This technique may assist in the visualization of optical scattering and refraction in micromanipulation and the creation of large optically bound matter crystals.