SGER: Detection of Optical Absorption from Individual Molecules Using Sagnac Interferometry

Stanford University, Stanford CA

Investigators

Abstract

Professors William E. Moerner and Martin M. Fejer of Stanford University are supported by the Analytical and Surface Chemistry and Atomic and Molecular Optics Programs to detect individual molecules using optical absorption and a Sagnac interferometer. The idea of this Small Grant for Exploratory Research is to avoid the dependence on fluorescence, which is the basis of most single molecule spectroscopy at present. Absorption would be a much more global approach, but is usually not as sensitive due to high background noise. Sagnac interferometry directly measures the difference in optical phase shift experienced by beams traveling clockwise versus counterclockwise in a ring. It is insensitive to excess phase amplitude and phase noise from the probing laser. Saturation modulation of the molecular absorption with a secondary pulsed laser will be used to make the molecular absorption time varying. By scanning the detection volume of the probe laser over the sample, microscopic images of ultrasmall features can be generated. The project has the potential to impact several fields including trace detection, biophysics, materials science, quantum information and nanoscience. In biological cells, for example, it would be possible to perform single molecule spectroscopy without dye labels, which potentially perturb the system, and without interference from spurious emitters.