Cavity-Enhanced High-Order Harmonic Generation: Transforming XUV and Attosecond Science High-order harmonic generation (HHG) plays a crucial role in producing coherent extreme ultraviolet (XUV) and soft X-ray light. However, traditional HHG techniques struggle with low efficiency, limiti... attosecond physics frequency comb high-order harmonics optical cavity spectroscopy ultrafast science XUV generation