What is a Helium-neon Laser?

Helium-Neon (HeNe) lasers utilize a tube filled with a mixture of helium and neon gases. Glow discharge excites the helium atoms, which then transfer their energy to neon atoms through collisions. Neon provides multiple laser transition wavelengths; the most common is 632.8 nm red light, while other wavelengths include 1.15 µm near-infrared, 543.5 nm green, 594 nm yellow, 612 nm orange, and 3.39 µm mid-infrared.

Specific wavelengths can be selected using appropriate resonator mirrors. Due to the low laser gain, resonator losses must be very small, typically below 1%.

The HeNe laser structure shown above is based on a glass tube that can be used with different mirror sets and is equipped with Brewster windows at both ends. Low-cost devices usually employ non-replaceable internal mirrors.

A typical HeNe laser features a gas cavity of approximately 20 cm in length, producing a continuous-wave (CW) laser at a wavelength of 632.8 nm with a power of a few milliwatts, while consuming several watts of electricity. The beam quality of HeNe lasers is generally excellent.

HeNe lasers, particularly the standard 632.8 nm version, are frequently used for alignment. Their primary competitors are laser diodes, which, while more compact and efficient, do not offer the same ease of use in terms of beam characteristics as HeNe lasers.