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 Φ n , 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 Φ n on the nature of the collision model and the experimental conditions, and (b) to indicate the limitations of present interpretations of experimental data.