Processes of Photoionization
Part of Laser Applications
Started in 2006, last modified in Feb 9, 2011
Ionization is the process by which an atom or a molecule loses one or more of its electrons, thus becoming an ion. The term photoionisation suggests that the ionization event is caused by light. What are the mechanisms responsible for the photoionization of materials, in the case of laser light?
The interaction of laser light with matter is a very complex subject. The effects depend on the properties of the material (composition and structure) as well as on the properties of the light (wavelength, intensity, and their temporal distribution, state of polarization, and the time during which the electromagnetic field is applied to the target). Several mechanisms can be activated simultaneously during the interaction, and can be somehow coupled to one another. The total photoionisation effect is thus the result of a combination of various mechanisms. Our goal is to isolate the ones that dominate in the experimental conditions that concern us, and to analyze them in order to understand their global effect. There are three important categories of photoionization mechanisms: single-photon ionization (SPI), multiphoton ionization (MPI), and avalanche ionization (AI). Depending on the experimental conditions, these three types of mechanisms contribute to generate one of the four photoionization modes, single-photon (SP), optical breakdown (OB), filamentary (F), and below OB threshold (B/OB), or a superposition of them.
Here we are concerned with laser applications, on a spectral domain that expands from UV to IR, in a pulsed regime (in which case we are interested in laser pulses with duration going from ns to fs), or a continuous regime.
Other processes
Self-Ionization
Photodissociation
Dissociative electron attachment