THE APPLICATION OF LOCK-IN AMPLIFIER IN PHYSICS TEACHING OF COLLEGE SPECTROSCOPY EXPERIMENTS

In current undergraduate physics experiment, the spectroscopy measurement mainly focuses on detecting the strong light signals from deuterium arc lamp or sodium-vapor lamp. However, in practice, it often needs to detect very weak light signal. Traditional technique, namely charge-coupled devices, was used to detect very weak light signals by a long-term integration. However, the high cost of this equipment makes it unable to be applied to undergraduate experimental teaching on a large scale. Lock-in amplifier uses a technique known as phase-sensitive detection to single out the component of the signal at a specific reference frequency and phase. It also can be used to collect the weak transmitted light signals in the semiconductor spectroscopy. Combined with its low price, it is expected to play an important role in undergraduate spectroscopy experiments. In the article, we built a semiconductor absorption spectroscopy based on the lock-in technique and spectrometer, and showed how to get weak signals in this setup. By analyzing and fitting the experimental data, we can get intensity of absorption as a function of energy of light, so that we can deduce the band gap of silicon materials.