Description
Why Plasma Harmonics?
Indeed, why plasma harmonics? Why we need plasma harmonics while we have a well-elaborated technique of frequency conversion of laser radiation through high-order harmonic generation (HHG) in gaseous media? One can remind that there is also another technique of HHG, surface harmonic generation. Both of them have a relatively long history of development, improvement, and application for various needs, and it seemed that those two methods fully satisfied scientific community from the point of view of creation of the sources of coherent extreme ultraviolet (XUV) radiation.
From the common point of view, the developments in our life should follow in accordance to simplicity and economy. Ptolemy stated [1], “We consider it a good principle to explain the phenomena by the simplest hypothesis possible.” This philosophical vision of everyday life later was developed in the principle of Ockham’s razor as a principle of parsimony, economy, or succinctness used in logic and problem-solving. It states that among competing hypotheses, the one that makes the fewest assumptions should be selected. Particularly, Ockham cited the principle of economy, Frustra fit per plura quod potest fieri per pauciora [It is futile to do with more things that which can be done with fewer]. It works well in life, but not in science. Moreover, the science itself is an example of broken Ockham’s razor principle, as new, more sophisticated ideas, which contradicted with commonly accepted and simplest explanations and approaches in description of the basics of our universe, finally completely changed our vision of the surrounding world.
But let us return from the heights of philosophical heaven to our Earth and start considering the new approach in optics, which have no aim to replace existing methods of the development of coherent short-wavelength sources, but just feels good enough to find its own place in this field of human knowledge. Is the principle “It is futile to do with more things that which can be done with fewer” applicable in science, and, particularly, in nonlinear optics? To answer on the question put in the title of this chapter, let us first briefly remind the history of gas and surface HHG, as well as best achievements of these techniques.
Contents
1 Why Plasma Harmonics?
2 Theoretical Basics of Plasma Harmonics
3 Low-Order Harmonic Generation in Plasma Plumes Using Nanosecond and Picosecond Driving Pulses
4 High-Order Harmonic Generation in Plasma Plumes Using Picosecond Pulses
5 Plasma HHG Using Femtosecond Pulses
6 Characterization of Plasma Harmonics
7 Recent Achievements in Plasma Harmonics