SIGNAL-TO-NOISE ENHANCEMENT IN OPTICAL SPECTROSCOPY OF SINGLE INDIUM IONS USING AMPLITUDE-MODULATION AND SYNCHRONOUS DETECTION

A technique for reducing background and improving the signal-to-noise ratio in optical spectroscopy of weak atomic transitions is described, In this technique an incident laser is square-wave amplitude modulate d and the resonance fluorescence from the atom is then detected out of phase with the excitation when the laser is off. Due to the finite li fetime of the atom's excited state, appreciable signal is observed whe n the laser is off and instrumental scattering background is virtually eliminated. Applying this technique to an experiment on single laser- cooled Inf ions, we have observed a factor of 500 reduction in backgro und and a factor of 5 increase in the signal-to-noise ratio. (C) 1997 American Institute of Physics.