定义：
基于非均匀光学增益导引光。

当激光光束在均匀介质中传输时，光束总会发生扩散。一个常用的防止光束扩散的方法是采用导波结构，称为波导，它具有空间分布的折射率。也可以通过单纯的采用空间变化的光学增益来实现导波，这称为增益导引。基本原理是：对光束中心部分的增益要大于光束两侧的增益，光束宽度变小，这一效应足够抵消光束衍射。 

注意增益导引通常需要结合非均匀的折射率，因为增益和折射率之间满足Kramers-Kronig关系。 

尤其对于高增益放大器，例如，脉冲泵浦的光学参量放大器，增益但因强烈影响放大光波的输出波形。这甚至会抑制这一装置的功率稳定性，因为信号光变得非常小以至于它与泵浦光束在最后一部分的非线性晶体中没有交叠。 

在一些激光二极管中，增益导引被用来对横向约束光场。这可以在一个装置中产生衍射极限的辐射，而这里波导结构只导引垂直方向的光场。 

在大多数固态激光谐振腔中，增益导引起的作用很小，因为这时增益相对较小，一些其它的效应更强。热透镜效应变得非常重要，对于强的超短脉冲，与克尔非线性相关的自聚焦效应也非常强。

Definition: guiding of light based on spatially inhomogeneous optical gain

When propagating in a homogeneous medium, a laser beam will sooner or later expand. A common method for preventing this expansion is to use a guiding structure, called a waveguide, with a spatially varying refractive index profile. It is also possible, however, to achieve guiding purely with a spatially varying optical gain, and this is called gain guiding. The basic idea is simple: by amplifying the center parts of the beam more than the wings of the spatial profile, the beam width will be reduced, and this effect may be strong enough e.g. to counteract diffraction.

Note that gain guiding is generally accompanied by some degree of guiding or anti-guiding via refractive index inhomogeneities, since gain and refractive index are related to each other via Kramers–Kronig relations.

Particularly in high-gain amplifiers, e.g. in optical parametric amplifiers with pulsed pumping, gain guiding can strongly influence the output profile of the amplified wave. This even leads to limitations of the power scalability of such devices [3], because the signal beam tends to become too small to overlap fully with the pump beam in the last section of the nonlinear crystal.

In certain laser diodes, gain guiding is used for horizontal confinement of the optical field. This allows for nearly diffraction-limited emission in a device where the waveguide structure guides only in the vertical direction.

In most solid-state laser resonators, gain guiding plays only a minor role, since the gain is relatively small and other effects are stronger. In particular, thermal lensing tends to be more important, and for intense ultrashort pulses there can also be a significant self-focusing effect related to the Kerr nonlinearity.

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