The International Laser Damage Competition results for 1064nm high-reflective coatings were announced in the 50th SPIE Laser-Induced Damage in Optical Materials Conference, which was held from Sep. 23 to 26, 2018 in Boulder, CO, USA. In the competition, the multilayer dielectric high-reflective coating from Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences, showed the best performance. Once again, SIOM won the first prize in this annual competition after 2012. 
    High damage resistance high-reflective coatings at 1064nm are designed for ICF-class lasers all around the world. This year, 33 samples were received from 18 well-known research institutions and commercial companies in six countries. To keep the test “blind”, each sample was placed in an identical packaging and was labeled with an alphanumeric sample code by a non-technical individual. The final test was carried out at Spica Technologies. The pulse length of the testing laser was 3ns with a repetition rate of 5Hz, and the wavelength was 1064nm.

Figure 1: The international laser induced damage competition results for the fundamental frequency reflective coatings in 2018

    As shown in Figure 1, laser induced damage threshold test indicates there is no damage until the incident laser intensity reaches 82 J/cm2, and the functional laser damage threshold is as high as 94 J/cm2. The high-reflective coatings can precisely manipulate the beam transmission in laser system, and directly affect the output energy and beam quality. The deposition techniques include e-beam evaporation, ion-beam assisted deposition and ion-beam sputtering. The choice for high-reflective index material could be HfO2, Al2O3, and Ta2O5. As shown in Fig. 2, the laser-resistance are different when prepared by the same deposition technique and material, reflecting the importance of coating design and deposition process.

Figure 2: The laser induced damage competition results for fundamental frequency reflective coatings in 2018, sorted by deposition technique.

    The Laboratory of Thin Film Optics of SIOM is the first research team focused on laser coating in China, and has a history of more than 50 years. Their laser coatings have been widely used in the Chinese high power laser systems.