High Sensitivity Frequency Modulation Spectroscopy and the Path to Single Molecule Detection.

Advances in optical spectroscopy rely on improved detection techniques that reduce noise to fundamental detection limits. When properly applied, frequency modulation laser spectroscopy (FM spectroscopy or FMS) approaches the quantum limit for detection. Having demonstrated that double modulation FMS could achieve such sensitivity in absorption spectroscopy, researchers raced to the goal of measuring the absorption of an individual molecule.