在激光科学中，激光束质量表示限定激光束的传播特性和变换特性（空间带宽准则）的内容。通过观察和记录的光束模式人们可以推断的光束之后的行为，如光束被障碍物遮挡后的空间模式特性;通过聚焦用透镜的激光束的最小光斑尺寸，次衍射极限或聚焦质量的计算。

Anthony E. Siegman 是第一个提出可以测量的光束质量因子的形式，除波长以为。 该因子被称为M, 其与光束性能紧密相关。然而M因子没有给出具体的空间分布特征，它表征了光束与基模高斯光束的接近程度。它确定了最小光斑尺寸和光束发散角。M 也指示了光束畸变比如，电诱导激光增益介质的热透镜效应，会使其变大。

In laser science, laser beam quality defines aspects of the beam illumination pattern and the merits of a particular laser beam's propagation and transformation properties (space-bandwidth criterion). By observing and recording the beam pattern, for example, one can infer the spatial mode properties of the beam and whether or not the beam is being clipped by an obstruction; By focusing the laser beam with a lens and measuring the minimum spot size, the number of times diffraction limit or focusing quality can be computed.