High harmonic generation featuring ultra-short pulses, short wavelengths and highly coherent radiation in a table-top setup has become one of the most versatile and affordable tools for studies of atomic and molecular dynamics as well as for nano-scale coherent diffractive imaging. In this book, we show the background and technical aspects of the generation and enhancement of high order harmonic radiations down to the water window region (2.3 - 4.4 nm). The source is specifically tailored and developed for imaging applications. By controlling and stabilizing the phase-matching condition in a gas cell, an extreme ultra-violet source which satisfies these requirements has been generated. Using a harmonic source with wavelengths around 30 nm, a resolution of 45 nm for a micrometer-size transmission sample has been obtained and biological-like absorption samples are also successfully reconstructed. A phase retrieval algorithm with a phase-curvature correction is developed to take advantage of the higher photon flux when placing the sample near the focus point.

Hoang Vu Le awarded a PhD degree at Swinburne University of Technology in 2015.Lap Van Dao is a Professor and Leader of Ultrafast Laser Science Group at Centre for Quantum and Optical Science, Swinburne University of Technology. Their research focused on the topic of high order harmonic generation and application of extreme ultraviolet radiation.