| This dissertation has measured the nanosecond laser induced damage threshold to HfO2/SiO2high reflective coatings, the damage mechanisms and morphologies were analyzed under various energy; laser conditioning to the samples by nanosecond laser show a result that there is an optimal energy range to improve the laser induced damage threshold.The laser damage mechanisms are discussed, the defects in the coatings are main reasons causing the damage, the methods to the improvement of resistance to laser damage are also put forward.The laser induced damage threshold(LIDT)measurements system is built base on the international standard of laser damage to optical surface. Half wave plate and polarizing prism are used to change the laser energy, then the output laser energy can be adjusted accurately. A CCD is used to online detect the plasma when damage happens and restore the results automatically.Laser damage threshold of HfO2/SiO2high reflective coatings by nanosecond laser is conducted utilizing the system, the results are obtained in accordance with the standard. Then the main damage mechanism of laser energy absorption by nodule defect in the coatings is put forward, and the coatings are formed to plasma with high temperature and pressure for the energy absorption, also the coatings are damage by plasma scald.Laser conditioning to HfO2/SiO2high reflective coatings of the same batch using nanosecond laser is carried out. The conditioned results tell that when the scanning laser energy is under35%of the unconditioned LIDT, the improvement of conditioned LIDT is14.62%, when scanning energy is between60%-75%, the LIDT increases35.55%; but when scanned with an energy greater than80%, it only rises5.145%. This shows that there exists an energy range which can maximally increase the LIDT of optical coatings during the single step conditioning.The conclusion can be the reference to study of improvement of laser damage resistance reflective coatings. |
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