An educational experiment on optical phenomena associated with an electrical discharge, plasma creation and light emission

The optical phenomena related to electrical discharges and to the technology of light production and material processing have been known for many decades. They have been adequately studied and widely applied. Therefore, exposure to the aforesaid optical phenomena as a learning exercise continues to impress and interest students in physics laboratories with essential learning results. With this in mind, we assembled a simple experimental apparatus which allows students to carry out experiments for the study of optical phenomena associated with electrical discharges and emission of radiation in a physics lab. A simple gas discharge flow system was utilized for observation of various coloured emissions as a function of experimental parameters, like molecular gas, discharge power, pressure and flow rate. Emission spectra were obtained using a laboratory spectrometer and emission bands were identified. Comparative spectra were also obtained with other light sources such as plasma globes and Geissler tubes of known gas composition. Distributions over vibrational states of some excited molecular states were measured and utilized to derive vibrational temperatures of vibrationally-electronically excited molecules