HeNeLaser

HeNelaser, more commonly known as the helium–neon laser or HeNe laser, is a gas laser that uses a mixture of helium and neon as its active medium. The most familiar emission is a red light at 632.8 nanometers, though other lines such as 594.1 nm (orange) and 543.5 nm (green) can occur under certain operating conditions.

Operating principle and construction

A HeNe laser relies on electrical discharge to excite the gas mixture. Helium atoms are excited to metastable states and transfer energy to neon atoms through collisional energy transfer. Neon then emits photons as it returns to lower energy levels, with the optical cavity formed by mirrors at each end of the discharge tube providing feedback to sustain stimulated emission. The tube is filled with a low-pressure mixture (typical a few Torr) and housed in a housing with a highly reflective mirror at one end and a partially transmitting mirror at the other to extract the laser beam. Common tube lengths range from tens of centimeters to about a meter, and the discharge is driven by a DC power supply at several hundred volts up to about a kilovolt.

history

The first continuous-wave HeNe laser was demonstrated in 1960 by Ali Javan, William Bennett, and Donald Herriott at Bell Telephone Laboratories, marking a milestone in gas-laser technology. The technology quickly became robust, compact, and relatively inexpensive to produce.

Applications and characteristics

HeNe lasers are widely used for optical alignment, interferometry, holography, and precision metrology, as well as in educational demonstrations and calibration tasks. They typically produce milliwatts of optical power with good beam quality and stable single-mode operation. Safety considerations include standard laser precautions; most low-power HeNe devices are Class 2 or Class 3R depending on output power.