Single molecule can shift the phase of a laser beam

Single molecule can shift the phase of a laser beam: To demonstrate how a molecule can change the phase of a light beam, the researchers detected organic molecules (dibenzanthanthrene) embedded in a solid matrix by performing coherent extinction spectroscopy at liquid helium temperature (near absolute zero). In this procedure, they tightly focused an excitation laser beam on the molecular sample in front of a mirror.
Next, the researchers arranged an interferometer consisting of two laser beams traveling the same path but with a small (115 MHz) frequency offset. As the laser frequencies traveled through the resonance of a single molecule, the researchers observed that the phase of one of the two interferometer beams was shifted by three degrees.