When a high-energy laser beam is focused through a lens onto a gas for any given laser intensity threshold, we can observe the creation of transient plasma. The dimensions of it depend on the focal length, the divergence of the laser beam and the pressure of the gas. This breakdown mechanism is the so-called “optical breakdown” of a gas and includes a static and a dynamic part.
The main mechanisms involved in the generation of the laser-induced plasma are multiphoton ionization and electron impacts leading to cascade breakdown
As a consequence of the laser-air interaction, the air is in a plasma state with ionization degree close to unity, temperature of 100000 K and number density of
2E20 cm -3.
The plasma then expands at supersonic velocity 10 7 cm/ s cooling down and inducing mechanical effects on the surrounding environment shockwaves in gases or cavitation bubbles in liquids.
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