Low Noise Signal Detection

Much of modern experimental physics involves pulling a small signal out of a forest of noise. The most common technique for this—and probably the most accessible to the undergraduate student—is phase-sensitive detection. While the implementation of this technique has evolved considerably since its invention by Bob Dicke in the 1940’s, the underlying principle remains the same. In this lab, participants will use a modern, DSP lock-in amplifier to learn both the underlying principles and practical applications of the method.

This workshop will cover the essentials of lock-in detection, along with fundamental and technical noise sources that limit the resolution of measurements. Participants will generate a small signal and use a lock-in to measure it, and they will measure amplifier noise and Johnson noise in the apparatus under a variety of conditions. This will set the foundation for understanding signal-to-noise ratio and its fundamental limits.

We will then send a pulsed laser beam to a distant mirror and reflect it back to a local detector, using the lock-in to measure the phase lag between the outgoing and returning beam, and thus measuring the speed of light in a laboratory setting.