Although the limit of detection (LOD) is a widely used means of indicating the detection power of an analytical technique, the application of conventional detection limit theory is not straightforward with respect to laser spectroscopic methods which are capable of detecting single atoms or molecules in the laser beam. In this paper, theoretical considerations in the detection and evaluation of these methods are addressed on the basis of a simple model of a typical laser spectroscopic experiment; in addition, the theoretical requirements for the precise counting of atoms, and factors which influence the signal variance in the model, are considered. Simple Monte Carlo computer simulations are used to verify and demonstrate the application of the theory of single atom detection (SAD) to typical experimental situations.
Christopher L. Stevenson and James D. Winefordner, "Estimating Detection Limits in Ultratrace Analysis. Part II: Detecting and Counting Atoms and Molecules," Appl. Spectrosc. 46, 407-419 (1992)