Optical cavities have found widespread use in interfacing to quantum emitters. Concerns about backreflection and resulting loss, however, have largely prevented the placement of optics such as lenses or modulators within high-finesse cavities. In this work, we demonstrate a million-fold suppression of backreflections from lenses within a twisted optical cavity. We achieve this by quantitatively exploring backscatter in Fabry–Perot resonators, separating the effect into three physical sectors: polarization, mode envelope, and transverse mode profile. We describe the impact of each of these sectors and demonstrate how to minimize backreflections within each. This culminates in measured effective reflectivities below the part-per-billion level for the fundamental mode. Additionally, we show that beams carrying orbital angular momentum experience up to {10^4}${10^4}$ times additional suppression, limited only by the density of states of other cavity modes. The understanding and techniques described in this work could expand the utility of optical resonators in topics ranging from quantum optics and cavity quantum electrodynamics to ring resonators and laser gyroscopes.

中文翻译：

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理解和抑制光学谐振器中的反向散射

光学腔已广泛用于与量子发射器的接口。然而，对背反射和由此产生的损耗的担忧在很大程度上阻碍了在高精密腔内放置透镜或调制器等光学器件。在这项工作中，我们展示了对扭曲光学腔内透镜的背向反射的百万倍抑制。我们通过定量探索法布里-珀罗谐振器中的反向散射来实现这一点，将效应分为三个物理部分：极化、模式包络和横向模式分布。我们描述了这些领域中的每一个的影响，并展示了如何最大限度地减少每个领域内的背向反射。这最终导致测量的有效反射率低于基模的十亿分之一水平。此外，{10^4}${10^4}$次额外抑制，仅受其他腔模式的状态密度限制。这项工作中描述的理解和技术可以扩展光学谐振器在从量子光学和腔量子电动力学到环形谐振器和激光陀螺仪的主题中的实用性。