Nanosecond laser-induced surface damage and its mechanism of CaF2 optical window at 248 nm KrF excimer laser

Xin Li; Xian-An Dou; Hong Zhu; Yue Hu; Xi Wang

doi:10.1038/s41598-020-62469-y

Nanosecond laser-induced surface damage and its mechanism of CaF₂ optical window at 248 nm KrF excimer laser

Sci Rep. 2020 Mar 26;10(1):5550. doi: 10.1038/s41598-020-62469-y.

Authors

Xin Li^{1

2}, Xian-An Dou^{1

2}, Hong Zhu³, Yue Hu⁴, Xi Wang^{5

6}

Affiliations

¹ State Key Laboratory of Pulsed Power Laser Technology, National University of Defense Technology, Hefei, 230037, China.
² Anhui Laboratory of Advanced Laser Technology, Hefei, 230037, China.
³ Key Laboratory of Polarization Imaging Detection Technology of Anhui Province, Army Artillery and Air Defense Academy, Hefei, 230037, China.
⁴ Hefei Second Sanatorium for Retired Cadres of Anhui Province Military Command, Hefei, 230061, China.
⁵ State Key Laboratory of Pulsed Power Laser Technology, National University of Defense Technology, Hefei, 230037, China. eastangus@126.com.
⁶ Anhui Laboratory of Advanced Laser Technology, Hefei, 230037, China. eastangus@126.com.

Abstract

Calcium fluoride (CaF₂) crystals is a kind of important optical material for ultraviolet (UV) and deep-ultraviolet (DUV) lithography and high-power laser-related applications. However, its laser-induced damage threshold (LIDT) directly affects the laser power, so that the above-mentioned applications could be limited. Therefore, the research on the damage characteristics and laser damage resistance of CaF₂ crystals is urgent. A 3D Finite-Difference Time-Domain (FDTD) method with Maxwell spinor equation is used, and the results show that the electric field intensity of rear surface is larger than that of front surface, which causes a lower threshold and is consistent with the experimental observations. And a thermo-mechanical coupled finite element model (FEM) of CaF₂ with Ce₂O₃ impurities, which are introduced by polishing process, has semiquantitatively described the damage mechanism of CaF₂ by 248 nm-excimer laser.

Abstract

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