High-order harmonic generation in laser surface ablation: current trends

We review emerging concepts that have increased the efficiency of coherent XUV (extreme ultraviolet) generation through the use of laser frequency conversion in specially prepared plasmas and which have enabled high-order harmonic generation (HHG) spectroscopy to be used in spectral and structural analysis. We also present the current status of plasma HHG and examine what new trends have evolved in the field since it was reviewed last [Phys. Usp. 52 55 (2009)1. In particular, we consider new techniques for generating higher harmonics from various plasmas for the purpose of studying the physical properties of materials. It has been shown recently that HHG has application potential for many, sometimes unexpected, areas of laser radiation matter interaction. It is argued that plasma HHG is along with alternative coherent XUV generation a powerful tool for a variety of spectroscopic and analytical applications.