Exploring Photoionization in Combination with Direct & Stepwise Ionization

[aquila14]

I'm working on a personal project trying to figure out if lasers can be effectively used to generate plasma from a gas at specific rates.

As part of this, I assumed that most of the ionization would take place because of the laser photons rather than the power generated by the laser. Working with this assumption, I'm now trying to figure out if there can be any direct ionization or stepwise ionization (from electron/ion impact) as a result of the photoionization. If so, how do you predict the percentage of each type of ionization?I've tried to look through a lot of textbooks and other sources, but haven't been able to find photoionization in combination with direct and/or stepwise ionization. This is my last ditch effort. I'll have to go with other assumptions if this theory doesn't pan out.

Please help!

Note: So far I haven't considered ionization equilibrium, so recombination doesn't factor in yet.

 

[Valerie Park]

Ionization from laser photons is indeed a valid concept. Depending on the type of laser and its wavelength, various ionization processes may be possible. Photodetachment, photodissociation, photoionization, and two-photon ionization are all mechanisms by which a laser can produce ions. Direct ionization occurs when an electron is removed from an atom or molecule due to a single photon interaction. It is typically observed with higher energy (eV) lasers and shorter wavelengths (UV). Stepwise ionization occurs when a series of lower energy photons interact with the atom or molecule, each photon removing an electron until the species becomes fully ionized. This is more common with longer wavelength lasers such as those in the infra-red regime. The percentage of direct and stepwise ionization depends heavily on the type of laser used, its wavelength, and the gas species. Some of this information can be obtained from data tables, such as the NIST Atomic Spectra Database or the HITRAN database. Additionally, if you are looking at specific gas mixtures, you may be able to find theoretical models that predict the ionization probability.