Metastable Helium

Long tubes of helium glow a soft pink, excited by the radio frequency discharge of the coils wrapped around them.
The delightful hue of this low-pressure helium gas is a side-effect of the RF discharge that keeps it in a metastable state.

August 23, 2015

When a handheld Tesla coil is activated in the vicinity of these long, transparent tubes of helium, they light up like a neon sign. A radio-frequency electromagnetic pulse, created in the copper bands along the length of the tubes, keeps them lit even after the Tesla coil has been turned off. In this semi-stable state, the helium's electrons can transfer angular momentum to the nucleus, effectively setting it spinning. By generating a uniform magnetic field and shining a circularly-polarized laser through the tubes, scientists can get a sample of helium-3 atoms all spinning along the same axis, for use in sensitive MRI-style imaging.