Particle accelerators and storage rings have been transformative instruments of discovery, and, for many applications, innovations in particle-beam cooling have been a principal driver of that success¹. Stochastic cooling (SC), one of the most important conceptual and technological advances in this area^2,3,4,5,6, cools a beam through granular sampling and correction of its phase-space structure, thus bearing resemblance to a ‘Maxwell’s demon’. The extension of SC from the microwave regime up to optical frequencies and bandwidths has long been pursued, as it could increase the achievable cooling rates by three to four orders of magnitude and provide a powerful tool for future accelerators. First proposed nearly 30 years ago, optical stochastic cooling (OSC) replaces the conventional microwave elements of SC with optical-frequency analogues and is, in principle, compatible with any species of charged-particle beam^7,8. Here we describe a demonstration of OSC in a proof-of-principle experiment at the Fermi National Accelerator Laboratory’s Integrable Optics Test Accelerator^9,10. The experiment used 100-MeV electrons and a non-amplified configuration of OSC with a radiation wavelength of 950 nm, and achieved strong, simultaneous cooling of the beam in all degrees of freedom. This realization of SC at optical frequencies serves as a foundation for more advanced experiments with high-gain optical amplification, and advances opportunities for future operational OSC systems with potential benefit to a broad user community in the accelerator-based sciences.

粒子加速器和储存环一直是变革性的发现工具，对于许多应用来说，粒子束冷却方面的创新一直是成功的主要驱动力¹。随机冷却 (SC)，这是该领域最重要的概念和技术进步之一^2,3,4,5,6，通过颗粒采样和校正其相空间结构来冷却光束，因此与“麦克斯韦恶魔”相似。长期以来，人们一直在追求将 SC 从微波范围扩展到光学频率和带宽，因为它可以将可实现的冷却速率提高三到四个数量级，并为未来的加速器提供强大的工具。近 30 年前首次提出，光学随机冷却 (OSC) 用光学频率类似物取代了 SC 的传统微波元件，并且原则上与任何种类的带电粒子束兼容^7,8。^{在这里，我们在费米国家加速器实验室的可积分光学测试加速器9,10}的原理验证实验中描述了 OSC 的演示. 该实验使用了 100-MeV 的电子和辐射波长为 950 nm 的非放大配置的 OSC，并在所有自由度上实现了光束的强同时冷却。这种在光学频率下实现 SC 为更高级的高增益光学放大实验奠定了基础，并为未来可操作的 OSC 系统提供了机会，从而为基于加速器的科学领域的广大用户群体带来潜在利益。