In laser physics, beam quality refers to how well a laser beam remains focused. The higher the quality, the less divergence in the beam. Beam quality can be affected by a number of factors, such as the type and quality of the laser's components, the type of laser gain medium used, the optical pumping method used, the power level and the mechanical and thermal stresses on the laser.
There is a trade-off between beam quality and beam power. When energy is pumped into the laser's gain medium, which the laser uses to amplify light, some of the energy will convert into heat. Excess heat can result in temperature gradients in the medium that produce a thermal lensing effect, reducing the beam's quality. This makes the type of gain medium used important.
