Lasermedium

A lasermedium, or gain medium, is the material that provides optical amplification in a laser by emitting photons through stimulated emission when excited to a higher energy state. The lasermedium is placed inside an optical resonator so that the generated photons pass through it multiple times, building up intensity.

Common forms include solid-state crystals and glasses doped with rare-earth or transition-metal ions (for example Nd:YAG, Ti:sapphire, Er:YAG); gaseous media such as carbon dioxide or helium-neon; liquid dye solutions (such as rhodamine 6G or coumarin 480); and semiconductor materials using quantum wells or quantum dots. Each type offers characteristic wavelengths, gain properties, and pump requirements.

Operation relies on achieving population inversion, typically by optical pumping (flash lamps, LEDs) or electrical pumping in semiconductor lasers. Key figures include emission cross-section, gain coefficient, and upper-level lifetime. The lasermedium's emission line width and temperature sensitivity influence the laser's spectral properties and efficiency. Thermal effects and photodegradation can limit performance.

Design and application depend on the lasermedium's wavelength, power handling, and stability. Material choice affects threshold, slope efficiency, and beam quality. Understanding the lasermedium is fundamental to laser engineering, enabling devices ranging from handheld pointers to industrial cutting systems and scientific instruments.