Høyharmoniskgenerering

Høyharmoniskgenerering, or high harmonic generation (HHG) in English, is a nonlinear optical process where an intense ultrashort laser pulse interacts with a material, typically a gas or solid, to produce coherent radiation at much higher frequencies. This generated radiation consists of discrete spectral lines that are integer multiples of the fundamental frequency of the driving laser.

The underlying mechanism involves the tunnel ionization of atoms or molecules by the strong laser field. Once an electron is liberated, it is accelerated by the laser's electric field. As the laser field oscillates, the electron oscillates and can be driven back towards its parent ion. Upon recombination with the ion, the electron releases its kinetic energy in the form of a photon. The energy of this photon corresponds to the harmonic order, meaning the frequency of the emitted photon is a multiple of the fundamental laser frequency.

HHG is a powerful tool for generating coherent extreme ultraviolet (XUV) and soft X-ray radiation. This coherent radiation has a wide range of applications in various scientific fields. It is used for studying atomic and molecular dynamics, probing electronic structures of materials, and in high-resolution microscopy and spectroscopy. The ability to generate ultrashort pulses in the XUV/soft X-ray regime also opens possibilities for time-resolved measurements of ultrafast phenomena. The efficiency and spectral range of HHG depend on factors such as the driving laser intensity, wavelength, pulse duration, and the properties of the target material.