定义：用于改变激光光束形状的光学装置。

通常来说，光束整形器（或者光束转换器）是可以改变光束形状的光学装置，即，改变其空间性质。
例如，存在折射和微光学光束整形器，可以将高斯型入射光束整形为平顶光束。 
另一种光束整形器与高功率激光二极管结合一起，例如，二极管线阵，是为了使光束半径和光束质量在两个正交方向上更加对称。
这有利于将光束射入具有圆形截面的光纤中，或者泵浦固态增益介质。在采用两个高反射镜和可以保持高亮度的一种常用的装置。
还有些装置采用了微光学结构，例如，包含小棱镜阵列的结构，实现与更小的器件类似的功能。
最初，这种亮度保持的光束整形器应用在二极管线阵上，但是它们也可以用于二极管堆中。 

图1：两反射镜的光束整形器的装置图。下面的部分表示从二极管线阵发出的细光束阵列被重新排列，在两个方向上都得到了几乎相等光束质量的光束。 
需要注意的是，有时简单的采用椭球形棱镜的组合不能够在两个方向上得到相同的斑点尺寸；

这样光束质量和光束发散角在两个方向上是不同的。如果用这种方法得到圆形焦点，那么光束发散角至少需要在一个方向上远大于光束整形器能得到的。 
还有其它的器件具有相同的功能，但是采用了其它的方法，例如，采用微光学或者光纤束。

后者情况下，二极管线阵的单个输出被耦合进光纤束中不同的光纤中，其中光纤束线性排列在二极管线阵附近，但是其输出端为圆形排列。 
有些光束整形器表现出不同的功能。

例如，有些器件用于纠正二极管线阵中的”笑脸”型光束或者使光束均匀，即使其强度分布更加均匀。

Definition: optical devices for modifying the shapes of laser beams

Alternative term: beam converters

In general, a beam shaper (or beam converter) is an optical device which somehow reshapes a light beam, i.e., it modifies its spatial profile. For example, there are refractive and micro-optic beam shapers which create a flat-top (top-hat) beam from a Gaussian input beam.

Another kind of beam shaper is often used in conjunction with a high-power laser diode, for example with a diode bar, in order to make both its beam radius and beam quality more symmetric with respect to two orthogonal directions. This facilitates e.g. launching the beam into an optical fiber with a circular cross-section, or pumping a solid-state gain medium. A popular type of device, which is based on two highly reflective mirrors and largely preserves the brightness, is described in Ref. [2]. Other devices are based on micro-optical structures, for example containing arrays of small prisms, to perform a similar function with a smaller device. Originally, such brightness-preserving beam shapers were applied to diode bars, but they can equally well be used with diode stacks.

Figure 1: Setup of a two-mirror beam shaper [2]. The lower part shows how an array of beamlets from the emitters of a diode bar is rearranged so as to obtain a roughly equal beam quality in both directions.

Note that it would not be sufficient simply to use a combination of cylindrical lenses so as to achieve equal spot sizes in both directions; the beam qualities and thus the beam divergence angles in both directions would then remain very different. If a circular focus is formed in that way, the beam divergence at least in one direction is much larger than achievable with a beam shaper.

There are other devices performing essentially the same function with other means, e.g. with diffractive micro-optics or with fiber bundles. In the latter case, the outputs of individual emitters of a diode bar are coupled into separate fibers of a bundle, which are arranged in a linear array on the side of the diode bar, but as a circular array on the output end.

Other beam shapers perform different functions. For example, there are devices for correcting the “smile” of diode bars [4].

Finally, there are beam homogenizers for making its intensity distribution more uniform.

Bibliography