Scientists Discover Excimer Laser-induced Damage Mechanism of CaF2 crystal

Mar 02, 2022 | By SHAO Jingzhen, ZHAO Weiwei

Research conducted in Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science (HFIPS), Chinese Academy of Sciences (CAS) described the damage mechanism of CaF2 crystal, an important component in the Ultraviolet Rays (UV) optical system, and concluded that it’s closely related to cleavage plane and sliding system.

The related results were published in Applied Surface Science.

The team, led by Prof. LIANG Xu and Prof. SHAO Jingzhen, studied the laser-induced damage characteristics with a self-developed KrF excimer laser, and analyzed the formation mechanism of surface morphology of three different crystal planes.

"We studied the cleavage plane {111}, the slip system {100}〈110〉, the angular relationship between the crystal plane, the slip system and cleavage plane," explained SHAO, "and found it's the structural characteristics of the CaF2 crystal that led to the different mechanical properties on different crystal planes."

CaF2 crystal directly affects the stability and life of UV optical system. Therefore, scientists have turned their attention to the process and mechanism of the interaction between UV laser and the CaF2 crystal to improve its laser damage resistance.

In this research, scientists completed laser irradiation experiment on CaF2 crystal with this 248 nm excimer laser. They obtained the evolution of damage morphology and the laser induced damage thresholds of three different CaF2 crystals planes (100), (110) and (111).

The results displayed different damage morphology. The damage of plane (111) showed the phenomenon of lamellar stripped, while there was a burst-like damage on plane (110) and plane (100), which originated from the crack or local damage point.

These results pave the way for the application of CaF2 crystals with different crystal planes in UV laser system.

This work was supported by the Scientific Equipment Development Project of the Chinese Academy of Sciences, Youth Innovation Promotion Association of the Chinese Academy of Sciences, National Natural Science Foundation of China, and the Open Research Fund of the State Key Laboratory of Pulsed Power Laser Technology.

The laser-induced damage morphology of the CaF2 crystal depends on the crystal structure (Image by SHAO Jingzhen)


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