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A helium–neon laser (HeNe) is a gas laser that uses a sealed tube containing a mixture of helium and neon gases as its gain medium. The most common lasing transition occurs in neon at a wavelength of 632.8 nanometers, producing a visible red beam. HeNe lasers are among the earliest practical continuous‑wave gas lasers and remain popular for their simplicity, stability, and clean visible output.

Principle of operation involves an electrical discharge that excites helium atoms. Through collisions, excited helium transfers energy to neon atoms, which then emit photons as they return to lower energy states. The optical cavity formed by mirrors at the ends of the discharge tube selects and amplifies the laser transition, yielding a coherent beam.

Construction and operation typically feature a compact glass discharge tube with internal electrodes, enclosed in a housing. A high‑voltage power supply or current source drives the discharge. The tube is designed for moderate operating pressures of the gas mixture. Typical laboratory HeNe lasers deliver output powers on the order of a few milliwatts (commonly around 1–10 mW), though higher‑power versions exist for specialized applications. The beam is usually well defined and can be internal to the tube or emitted through a front face with a partial‑transmission mirror.

Variants exist that can lase at other neon transitions under particular conditions, but 632.8 nm remains the standard line for most commercial devices. HeNe lasers are widely used for alignment, holography, metrology, spectroscopy, and educational demonstrations due to their robustness, long lifetimes, and ease of use.

Safety considerations include eye hazard from direct or reflected beam and the need to handle high‑voltage components with proper precautions.