Large Optics: Petawatt high-LIDT coatings don’t sacrifice performance
Over the past decade, an increasing number of (mainly government-financed) large petawatt laser systems have been built or are planned for construction. The world map of ultrahigh-intensity laser capabilities compiled by C.P.J. Barty (ICUIL 2012) at the National Ignition Facility (Livermore, CA) lists a total of 71 sites that are involved in high-power laser systems, with 16 sites in North America, 30 in Europe, and 25 in Asia.
In the past, development of such powerful laser systems was hampered by the lack of suitable laser materials, but since the development of chirped pulse amplification (CPA) in the mid-1980s this issue has been overcome for short pulse lengths. Rapid development has taken place in this field, with applications including studies in high-energy-density physics, flash x-radiography, and laser-ignited nuclear fusion.
According to some predictions (ICUIL 2011), the generation of laser intensities of up to 1024 W/cm2 and the generation of gamma-ray pulses of about 100 yoctoseconds (10-22 s) is possible. As of 2010, the peak power of the world's most powerful laser (again according to ICUIL 2011) was approximately 11.5 PW, but by the end of 2015 this is planned to increase to approximately 127 PW. In addition, several exawatt-scale projects are currently in the planning stage.
To meet these demands, it is critical to concurrently develop high-performance laser optics that offer high laser-induced damage threshold (LIDT) without sacrificing spectral or phase performance. Although the optics can be made larger to lower the power density, this approach inevitably increases both the size and cost of the system. A compromise must be found, with the LIDT being the key parameter when considering the most appropriate beam size.