Quasi-phase-matching of high harmonic EUV radiation

We demonstrate that in the EUV we can apply quasi-phase-matching techniques to high-harmonic generation. Using a hollow-core waveguide with a periodically-modulated diameter, we show that the wavelength range over which we can efficiently generate phase-matched high-harmonics can be extended to shorter wavelengths. The periodic structure modulates the generation of high harmonics and restricts HHG to regions with favorable constructive interference. Furthermore, we show that our approach results in bright emission at wavelengths of interest to lithography (13 nm), and we expect that the QPM technique can be extended to shorter wavelengths, allowing the generation of bright phase-matched coherent EUV light at "water window" wavelengths.