This is an experiment in optical spectroscopy: the accurate determination of
the energy of the light quanta emitted by atoms. You will first learn some
optics and how a spectrograph works. Then you will rapidly chop the light from
the source and learn how to detect faint light by measuring the in-phase
component of the chopped light using a photodiode and a lock-in amplifier
(one of the experimentalist's most useful and powerful tools for recovering
signals otherwise hopelessly buried in noise.) The goal is to study the emission
lines of hydrogen and its heavy cousin deuterium.