High power laser mirrors for PW and TW lasers

The scary TW and PW lasers deliver incredibly high peak powers and are capable of reaching laser pulses characterized by tens of femtoseconds, hundreds of joules, and high repetition rates, which can be used to investigate interesting phenomena, including ultrafast processes in physics, chemistry, and biology. These types of lasers are investigated in many facilities, including ELI-NP (Romania), J-Karen-P (Japan), SULF (China), LaserNet US facilities, such as CSU, LBNL, LLNL, OSU, and many more.

 

While the laser systems at these facilities are scary due to their extreme peak powers, they are also astonishingly big. For example, the user facility of the ZEUS laser (Zettawatt-Equivalent Ultrashort pulse laser System) system at the University of Michigan, which will be able to reach 3 PW peak powers, is enclosed in ~16,000 square feet of space.

 

These facilities revolve around different systems and concepts to reach the extreme values of TW and PW lasers. While several approaches to achieve petawatt class laser pump sources are viable, many of the systems center around OPCPA/CPA (stretch, amplify, compress approach) Ti:Sapphire laser, while some use Nd:Glass amplifiers. An important point to consider when speaking of the specific systems is that neodymium-based laser systems offer high energy but are limited by the wavelength bandwidth. To overcome this, titanium oscillators with optical parametric amplification (OPCPA) are used, boosting both energy and bandwidth to produce the extreme values of TW and PW lasers. Ongoing research aims to further enhance the power and efficiency of these laser systems and achieve ultrashort pulse duration, high average power and high repetition rate simultaneously. Moreover, innovation in optical components, including high power laser mirrors, and their use in high-power laser research, such as Multipass Cells (MPC), will continue to drive progress in this field. Whatever laser the PW & TW system is built on, such high-power lasers must contain laser high power laser mirrors and optics that withstand huge amounts of energy while maintaining the necessary spectral performance. This comes as a challenge for coating manufacturers. The most suitable coating technology for manufacturing laser optics for these systems is Ion Beam Sputtering (IBS), which OPTOMAN relies solely on. The bulk-like density and precision of manufactured coatings not only increase the spectral performance but minimise losses, including absorption. Developing such optimised coatings is crucial to achieve high damage resistance, maintain wide bandwidths, and ensure precise spectral phase control. But a machine is of no use if it’s not used properly – the intermediary between the coating design and the machine is by far the most important component in this equation. That intermediary is the highly skilled and experienced coating engineers that OPTOMAN is proud of.

OPTOMAN, by mastering the IBS technology, pre- and post-coating processes, with extensive R&D in handling different material substrates, coating designs, and even substrate shapes (including parabolic), has developed products that are suitable for these systems and thrive in TW & PW peak power environments, by featuring:

• Very high LIDT, reaching values such as 1.4 J/cm^² @ 800 nm, 47 fs, 100 Hz, 97.6 µm.
• Excellent spectral performance (HR>99.99% @ 980-1080 nm)
• Low absorption (<1 ppm @ 1030 nm)

One of the most challenging coatings to design and manufacture is high power laser mirrors for Multipass Cells (MPCs). The main requirements for an MPC mirror are large reflection bandwidth, high reflectivity, high LIDT, and low group delay dispersion (GDD). OPTOMAN sees considerable potential for MPCs as their adoption in laser systems might help reach TW & PW peak powers. For this reason, OPTOMAN developed dielectric high power laser mirrors optimised specifically for MPC applications. OPTOMAN offers flat, concave, and convex broadband mirrors that possess all the features mentioned before high reflectivity (R>99.98%), high LIDT (>0.7 J/cm^² @ 1030 nm, 180 fs), and low and spectrally uniform GDD. Read more about mirrors for Multipass Cells.

LIDT measurement of the OPTOMAN MPC mirror demonstrates that the mirrors don’t suffer from the degradation effect. The laser fluence level that causes damage remains constant, even with an increasing number of pulses. This is extremely important and beneficial for powerful ultrafast lasers, as the mirror has an enhanced lifetime. These high power laser mirrors ensure long-term reliability in demanding applications, making them a critical component in high-intensity laser systems.

Overall, the advancements in TW and PW lasers represent a big leap forward in photonics. The combination of ultra-short, high-energy pulses has opened the way for numerous scientific, medical, and industrial applications. As researchers continue to explore these technologies, the impact of TW and PW lasers on the ability to innovate will only grow stronger. None of it would be possible without application-optimised high power laser mirrors and laser optics—because your laser is only as strong as its weakest link.