Extremely short, high-energy pulses are essential in modern ultrafast science. In a seminal paper in 1996¹, Nisoli and co-workers demonstrated the first intense pulse compression employing a gas-filled hollow-core fibre. Despite the huge body of scientific work on this technology stemming from ultrafast and attosecond research, here we identify an unexplored few-cycle visible-light generation mechanism, which relies on the nonlinear mixing of hollow-core fibre modes. Using a commercially available ytterbium laser, we generate 4.6 fs, 20 μJ pulses centred at around 600 nm (~2 cycles, ~4 GW peak power), ~40 times shorter than the input 175 fs, 1 mJ pulses at 1,035 nm. Our approach thus directly projects few-hundred-femtosecond-long infrared pulses into the single-cycle regime at visible frequencies, without the need for additional post-compression. As a powerful application of our findings, we present a compact, multicolour pump–probe set-up with a temporal resolution of a few optical cycles.

极短的高能脉冲在现代超快科学中是必不可少的。在 1996 年的一篇开创性论文中¹，Nisoli 和他的同事展示了第一次使用充气中空纤维的强烈脉冲压缩。尽管这项技术的大量科学工作源于超快和阿秒研究，但我们在这里确定了一种未探索的少周期可见光产生机制，它依赖于空心光纤模式的非线性混合。使用市售的镱激光器，我们产生了 4.6 fs、20 μJ 脉冲，中心波长约为 600 nm（~2 个周期，~4 GW 峰值功率），比输入 175 fs、1 mJ 脉冲在 1,035 nm 处短约 40 倍。因此，我们的方法直接将几百飞秒长的红外脉冲投射到可见频率的单周期状态中，而不需要额外的后压缩。作为我们发现的有力应用，我们提出了一个紧凑的，