Broadband nano-focusing of high-order harmonics in soft X-ray region with ellipsoidal mirror

We demonstrate broadband focusing of multiple high-order harmonics of intense femtosecond laser pulses using an ellipsoidal mirror. The ellipsoidal mirror, with a high numerical aperture and a highly accurate surface, was fabricated using a replication process. The multiple high-order harmonics in the wavelength range between 10 and 20 nm were focused to the nearly diffraction-limited size of 350 × 380 nm2. According to Rayleigh's quarter...