A Software-Based Lock-In Measurement for Student Laboratories

A student laboratory experiment is presented that introduces the concept of a lock-in measurement through the exploration of the relationship between the power detected from a modulated light source and the distance between the source and the detector. The lock-in measurement is done in software using time streams for both the reference and the detector signals. The achievable experimental sensitivity is shown to increase several orders of magnitude over the simple case without using modulation. In addition, the student becomes familiar with computational techniques pertinent to large data sets.