Brillouin scattering has applications ranging from signal processing^1,2, sensing³ and microscopy⁴ to quantum information⁵ and fundamental science^6,7. Most of these applications rely on the electrostrictive interaction between light and phonons^3,7,8. Here we show that in liquids optically induced surface deformations can provide an alternative and far stronger interaction. This allows the demonstration of ultralow-threshold Brillouin lasing and strong phonon-mediated optical coupling. This form of strong coupling is a key capability for Brillouin-reconfigurable optical switches and circuits^9,10, for photonic quantum interfaces¹¹ and to generate synthetic electromagnetic fields^12,13. While applicable to liquids quite generally, our demonstration uses superfluid helium. Configured as a Brillouin gyroscope¹⁴ this provides the prospect of measuring superfluid circulation with unprecedented precision, and exploring the rich physics of quantum fluid dynamics, from quantized vorticity to quantum turbulence^15,16.

布里渊散射的应用范围从信号处理^1,2、传感³和显微镜⁴到量子信息⁵和基础科学^6,7。大多数这些应用依赖于光和声子^3,7,8之间的电致伸缩相互作用。在这里，我们表明，在液体中，光学诱导的表面变形可以提供另一种更强大的相互作用。这允许演示超低阈值布里渊激光和强声子介导的光耦合。这种形式的强耦合是布里渊可重构光开关和电路^9,10的关键能力，用于光子量子接口¹¹并产生合成电磁场^12,13。虽然相当普遍地适用于液体，但我们的演示使用超流氦。配置为布里渊陀螺仪¹⁴这提供了以前所未有的精度测量超流体循环的前景，并探索量子流体动力学的丰富物理学，从量子涡度到量子湍流^15,16。