When an intense laser pulse interacts with a solid, liquid or gas, it very quickly drives it into the fourth state of matter; plasma. A plasma is formed when electrons are released from their host atoms in the presence of the extremely high electric fields of the laser, generating a gaseous soup of subatomic particles consisting of ions and electrons.
All types of radiation are given off during a high power laser-plasma interaction, including beams of electrons, protons, ions, X-rays, gamma rays and neutrons. The radiation is sampled using various diagnostics in the target chamber, which can give you information about the interaction, such as the plasma temperature. The laser-plasma only exists for the briefest of times, much less than a billionth of a second, but a lot of very interesting and useful physics can go on in that time.
