Basis and Use of Lock-In Detection in Analytical Spectrometry

The basic lock-in amplifier model will be briefly surveyed in order to present a few critical guidelines for its usage in analytical spectrometry. Expressions for the impulse response, time variant impulse response, the variant transfer function, the power transfer function, and the time variant time autocorrelation function of the lock-in amplifier are given. Figures of merit for the lock-in including the noise bandwidth and the signal-to-noise-improvement ratio are also given. The general conditions which must be met for successful shot noise limited application of lock-in detection are presented as well as how these conditions are applied to actual spectrometric systems.