Sulfur lamp in microwave field

This closeup shot shows a variant of the Philips S1000 being driven by microwave energy from a domestic oven. Here the lamp is still cold and the plasma runs in argon and some sulfur vapor, which is blue at low pressure (see glowing vapor at right, close to the waveguide's output). Interestingly some striations can be seen in the argon plasma, which are caused by a slower propagation of the electromagnetic wave there that in the rest of the microwave oven's cavity. In air, where the EM wave's group velocity is close to that of light in vacuum (n=1.0003 at 2.45 GHz), the wavelength is 12.23 cm while it can be estimated to be in the 5.9-16.3 mm range in the lamp in its present state, corresponding to a local refractive index between 7.5 and 20.7.