A helium-neon (HeNe) laser is a type of gas laser that emits visible red light at a wavelength of 632.8 nanometers (nm). It operates based on the principle of stimulated emission of photons from excited helium and neon atoms within a sealed glass tube filled with a mixture of these gases.
Here are the key features and characteristics of HeNe lasers:
Gas medium: HeNe lasers use a mixture of helium (He) and neon (Ne) gases as the lasing medium. Typically, the helium serves as the primary energy source, providing an excited state for the neon atoms to undergo stimulated emission and produce laser light.
Optical resonator: HeNe lasers consist of an optical resonator, which typically includes two mirrors positioned at the ends of a cylindrical glass tube containing the gas mixture. One mirror is fully reflective, while the other is partially reflective, allowing some of the laser light to escape and be used for applications.
Population inversion: In a HeNe laser, the helium atoms are excited to higher energy levels through an electrical discharge or radiofrequency excitation. These excited helium atoms then transfer energy to the neon atoms through collisions, causing the neon atoms to become excited to higher energy levels. When the neon atoms transition back to lower energy levels, they emit photons, some of which undergo stimulated emission to produce coherent laser light.
Visible red light: HeNe lasers emit coherent light predominantly at a wavelength of 632.8 nm, corresponding to the red-orange region of the visible spectrum. This wavelength is well-suited for various applications, including alignment, positioning, holography, interferometry, and laser-based displays.
Low power and stability: HeNe lasers typically operate at low power levels, ranging from a few milliwatts to tens of milliwatts. They are known for their stability, long coherence length, and narrow linewidth, making them suitable for applications requiring precise and stable laser light.
Long lifetime: HeNe lasers have a relatively long operational lifetime, with lifetimes ranging from thousands to tens of thousands of hours under proper operating conditions. This longevity makes them reliable light sources for many applications.
Compact and portable: HeNe lasers are often compact and portable, with self-contained designs that include power supplies and cooling systems within the laser housing. This makes them convenient for laboratory use and field applications.
Limited applications: While HeNe lasers offer stable and coherent output, their limited output power and relatively high operating voltages make them less suitable for high-power industrial applications compared to other types of lasers such as diode lasers and solid-state lasers.
Overall, HeNe lasers are widely used in scientific research, metrology, instrumentation, and educational demonstrations due to their stable output, narrow linewidth, and visible red light emission. However, their use has become somewhat limited in recent years with the development of more efficient and compact laser technologies.