HeliumCadmium

Helium-Cadmium lasers, often abbreviated as HeCd lasers, are gas lasers that produce coherent light in the blue and ultraviolet portions of the electromagnetic spectrum. They operate by exciting a mixture of helium and cadmium vapor. The primary laser transitions occur in the cadmium ions, with helium acting as a transfer medium to excite the cadmium atoms. The most common HeCd laser lines are at 441.6 nanometers (blue) and 325.0 nanometers (ultraviolet).

These lasers are known for their relatively high power output in these specific wavelengths, especially compared to other gas lasers of similar size. They are typically excited by a direct current discharge through the gas mixture, although radiofrequency excitation is also possible. The design involves a sealed tube containing the helium and cadmium, with mirrors forming the optical resonator. The cadmium is usually introduced in solid form and vaporized by the heat of the discharge.

Helium-Cadmium lasers have found applications in various scientific and industrial fields. Their blue output at 441.6 nm is useful for fluorescence microscopy, photodynamic therapy, and certain types of spectroscopy. The UV line at 325.0 nm is employed in photolithography, holography, and materials processing. However, HeCd lasers have a limited lifespan due to the consumable nature of the cadmium and can be more complex to maintain than some other laser types. They have largely been superseded by semiconductor diode lasers and solid-state lasers in some applications due to advancements in those technologies.