LASERS AND LASERS EXPERIMENTS
| Optical Breakdown in air with q-switch Nd:YAG laser
|12 MW laser beam focalised in air, produce an spark in air at the focus of the lens.
The Optical Breakdown in air can also be initiated by intense light, i.e. by electromagnetic waves with frequencies of hundreds of terahertz. The high optical intensities required can be reached in pulses as generated in a Q-switched laser (with nanosecond durations) or in a mode-locked laser . The intensity required for optical breakdown depends on the pulse duration. For example, for 1-ps pulses an optical
intensity of ≈ 2 × 1013 W/cm2 is required.
The effect is a strong local ionization of the medium, where the plasma reaches densities beyond the critical value (between 1020 and 1022 electrons/cm³). Once
the plasma critical density is achieved energy is very efficiently absorbed from the light pulse, and the local plasma temperature increases dramatically.
An explosive Coulombian expansion follows, and forms
a very powerful and damaging shockwave through the material that develops on ns timescale