Key characteristics of laser gain medium

What are the key characteristics of laser gain media?

Laser gain medium, also known as laser working substance, refers to the material system used to achieve particle population inversion and generate stimulated radiation to achieve light amplification. It is the core component of the laser, carrying a large number of atoms or molecules, these atoms or molecules under the excitation of external energy, can transition to the excited state, and through the excited radiation released photons, thus forming a laser light. The laser gain medium can be a solid, liquid, gas or semiconductor material.
In solid-state lasers, the commonly used gain media are crystals doped with rare earth ions or transition metal ions, such as Nd:YAG crystals, Nd:YVO4 crystals, etc. In liquid lasers, organic dyes are often used as gain media. Gas lasers use gas as a gain medium, such as carbon dioxide gas in carbon dioxide lasers, and helium and neon gas in helium-neon lasers. Semiconductor lasers use semiconductor materials as the gain medium, such as gallium arsenide (GaAs).
Key characteristics of the laser gain medium include:
Energy level structure: The atoms or molecules in the gain medium need to have a suitable energy level structure in order to achieve a population reversal under the excitation of external energy. This usually means that the energy difference between the higher and lower energy levels needs to match the photon energy of a particular wavelength.

Transition properties: Atoms or molecules in excited states need to have stable transition properties in order to release coherent photons during excited radiation. This requires the gain medium to have high quantum efficiency and low loss.
Thermal stability and mechanical strength: In practical applications, the gain medium needs to withstand high power pump light and laser output, so it needs to have good thermal stability and mechanical strength.
Optical quality: The optical quality of the gain medium is critical to the performance of the laser. It needs to have high light transmittance and low scattering loss to ensure the quality and stability of the laser beam. The choice of laser gain medium depends on the application requirements of the laser, working wavelength, output power and other factors. By optimizing the material and structure of the gain medium, the performance and efficiency of the laser can be further improved.