Two 6 um microspheres, ring-stained with a fluorescence dye, held in separate traps.  Less than 0.1 mW of power from the 488 nm blue beam of an argon-ion laser is focused in a trapping configuration, located one particle diameter to the right of the rightmost sphere.  This beam (not visible in the picture) excites the dye, causing the spheres to fluoresce.  The resulting fluorescence spectra exhibit resonance lines that split as one sphere is brought close to the other.

Another pair of 6 um fluorescent microspheres held in separate traps, along with an argon ion beam, as detailed above.  As the leftward sphere is brought toward the stationary rightward sphere and the argon-ion beam, of course its fluorescence increases.  But watch for the significant decrease in the leftward sphere's fluorescence when the rightward sphere is allowed to escape from its trap.