Analysis of ``Lock-In'' Detection of Modulated Molecular Beams Scattered from Solid Surfaces

Abstract

The ``lock-in'' technique (i.e., narrow-band amplification and phase-sensitive detection) for detecting modulated molecular beams is analyzed for the case of scattering from solid surfaces. A general method is described for computing An and Φn, the amplitude and phase of the output signal. Since this computation requires the assumption of a gas—solid collision model, we have selected three different models for a comparative study. Special consideration is given to the ``hard-cube'' model [Logan and Stickney, J. Chem. Phys. 44, 195 (1966)]. Numerical results are presented (a) to illustrate the dependence of An and Φn on the nature of the collision model and the experimental conditions, and (b) to indicate the limitations of present interpretations of experimental data.