The Fox-Smith mirror (FSM) has long been used in a three-mirror laser cavity arrangement for forcing the laser oscillation on a single-longitudinal mode. However, its transverse properties are very little studied, and we report three interesting transverse features. First, the FSM gives the possibility to change the order p of the oscillating radial Laguerre–Gaussian LG_p0 mode by adjusting the microscopic position of one of its mirrors. These results help for understanding non-interpreted experimental observations of interferometric control of the oscillating transverse mode reported by Smith in 1965. Second, we have shown that otherwise values of FSM parameters allow an equal FSM reflectivity of LG₀₀ and LG₀₁ (doughnut) modes. This would in effect give, to a laser using a FSM as rear mirror, a simultaneous oscillation of these two transverse modes giving rise to a shape-invariant flat-top laser beam. The latter having the interesting property to keep its uniform transverse intensity profile as it propagates inside and outside the laser cavity. Third, we have shown that the beam emerging from the FSM output through its beam splitter can be an Optical Bottle Beam by an adequate choice of parameters.

Fox-Smith 反射镜 (FSM) 长期以来一直用于三反射镜激光腔排列中，以迫使激光在单纵模式下振荡。然而，它的横向特性很少被研究，我们报告了三个有趣的横向特征。首先，FSM 提供了通过调整其中一个反射镜的微观位置来改变振荡径向 Laguerre-Gaussian LG _p0模式的阶数p的可能性。这些结果有助于理解 Smith 在 1965 年报告的对振荡横模干涉测量控制的非解释实验观察。 其次，我们已经表明 FSM 参数的其他值允许 LG ₀₀和 LG _{01 的}FSM 反射率相等（甜甜圈）模式。这实际上会给使用 FSM 作为后镜的激光器提供这两种横向模式的同时振荡，从而产生形状不变的平顶激光束。后者具有有趣的特性，可以在激光腔内外传播时保持其均匀的横向强度分布。第三，我们已经表明，通过其分束器的FSM输出的光束可以通过足够的参数选择光瓶梁。