What is the active medium used in a HeNe laser?

The active medium in a Helium-Neon (HeNe) laser is a mixture of helium and neon gases. In a HeNe laser, electrical discharge excites the helium atoms, which then transfer energy to the neon atoms. This energy transfer is essential for the laser action because it promotes the neon atoms to a higher energy state. When these excited neon atoms return to their ground state, they release energy in the form of photons, producing coherent light at specific wavelengths, commonly in the red region of the spectrum (632.8 nm).

The choice of helium and neon is crucial due to their specific physical properties and the way they interact, allowing for efficient laser operation. Helium's ability to facilitate energy transfer to neon makes this combination particularly effective for laser applications.