In optical experiments and applications, when selecting optical elements, a very important factor is whether the optical elements can withstand the influence of optical radiation, which is particularly important in high-power laser applications. There are three main forms of optical element damage caused by optical radiation: The first is the thermal effect caused by light absorption; the second is the dielectric breakdown caused by the radiation of short pulse laser; the third is the chemical bond damage caused by the extremely high peak power under the ultra short pulse laser. The parameter to measure the ability of an optical element to withstand light radiation is the laser damage threshold.
Laser damage threshold is an important parameter to characterize the ability of laser irradiated medium to resist laser damage. The high concentration of laser energy will cause local deformation or even complete damage to the interior or surface of the medium. The maximum laser power that a medium can bear per unit area is called the laser damage threshold of the medium.
1. It is closely related to the properties of the medium itself, including its composition, optical uniformity, optical absorption, thermal properties, etc;
2. It is related to the laser properties, including laser frequency, laser pulse width, laser beam spot, etc;
3. It is related to the processing process of optical elements, such as the processing traces left on the optical elements, coating methods, purity of film materials, and even the cleanliness of the experimental operation space will affect the damage of the medium.
Laser damage threshold, continuous laser and pulse laser should be different, continuous laser is the unit of power in W Watt, and pulse laser is the unit of work in J Joule, which is related to pulse width. If we convert the success rate of pulse laser work: 10J / 10ns = 1000MW, then the equivalent power of pulse laser is 1000MW. So, if the damage threshold of a mirror is 15J/ cm2@10ns , which is equivalent to 1000MW / cm2.