Photonics Lights Up Fusion

Imagine a world where we could harness the same energy that powers the stars, providing a virtually limitless and clean source of power. This is the promise of nuclear fusion, a process that has the potential to revolutionize our energy landscape. Magnetic confinement and inertial confinement are two promising technologies that can achieve fusion, and the reality of sustainable clean energy generation.  

Laser driven inertial confinement was used by the National Ignition Facility (NIF) to achieve the landmark result of positive gain.  This has accelerated development efforts, and the timeline for commercialization.  The path to viable power plants has both scientific and engineering challenges, as well as securing supply chain partners capable of delivering cost-effective, reliable devices and products.  The very high pulse energies needed for laser fusion requires photonic products to perform and operate far beyond mainstream laser applications.  This is the main issue for the supply chain.

With many decades of supplying all shapes and sizes of laser and delivery optics Coherent is uniquely positioned to support the development of inertial fusion energy. From optical fibers and non-linear crystals to diode lasers, our comprehensive suite of products and solutions is helping to drive the progress of fusion research

Let’s explore the critical role that photonics technology plays in advancing laser fusion technology. 

Coherent Components for Fusion

Coherent has been supplying the fusion community with a variety of photonic components tailored to meet the demanding requirements of generating the laser and the beamlines -  

Diode Lasers: High-power laser diode components are mission critical in fusion applications, particularly in driving Diode Pumped Solid State Lasers (DPSSLs), which are central to initiating fusion reactions. Their wall plug efficiency directly impacts the overall energy efficiency of the system, ensuring that maximum energy is delivered with minimal loss and minimum operational costs of energy-intensive fusion processes. 

High-power laser diodes are mass producible, while their wavelength can be precisely matched to the absorption wavelength of the DPSSL medium, ensuring optimal energy transfer. Peak power is also essential, as high-intensity pulses are required to achieve the extreme conditions needed for fusion. 

The small size of high-power laser diodes allows for dense packing, enabling the scaling of laser diode arrays needed for high-power applications. Longevity, or the operational lifetime, has been demonstrated for such diodes, which is key for reliable operation over extended periods, required for commercial fusion reactors to be viable. Long-lasting diodes reduce maintenance and replacement costs, enhancing the overall system's reliability and economic feasibility.  

Turnkey 350kW QCW diode pump module, which combines the beam from 100 Stacks of 8-bars each, into a homogenized beam with quadratic cross section of 78 mm x 78 mm.

Large Optics: The large beam diameters used to mitigate optical damage greatly increases optical aperture's, with some optics up to 1m (39”) in diameter.  Focusing with transmissive optics requires extremely high-precision, large sized optics that must withstand the high intensities and harsh environments typical of fusion facilities. 

We provide NIF with the wedged focus lenses (WFLs) used in their “Final Optics Assembly.” Each WFL is a 400 mm x 400 mm sized, 7.7 m focal length, off-axis aspheric lens made from high-quality fused silica. We employ a suite of computer-controlled polishing and measurement tools to achieve the extraordinary level of precision NIF demands for these components. We are one of just a handful of manufacturers worldwide who can consistently produce such large-aperture, precision-aspheric optics in high volume.

Large aperture 400 x 400 mm wedge lenses used in the National Ignition Facility undergoing testing.

Optical Fibers: Coherent provides a comprehensive range of specialty fibers designed for optimal performance, offering the lowest photodarkening, highest absorption rates, and large mode field areas. These fibers are ideal for scaling single-frequency, ultrafast, and high-power lasers. Frequently paired with our XLMA fibers, they play a crucial role as seed injection lasers in high-energy fusion research.

Crystals: Both gain crystals and non-linear frequency conversion crystals are used extensively throughout the amplifiers in a petawatt class laser system. The final stage of most fusion lasers requires frequency tripling of the laser that is achieved in two stages using two crystals.  The efficiency of the conversion improves with power density; however, this is balanced with damage thresholds. There are significant challenges to producing large aperture crystals, however we are able to lean on decades of commercial success to continually push the sizing envelope. 

Laser Diagnostics: Laser measurement for fusion research involves precise monitoring and control of both seed and high-power lasers. Coherent offers a broad range of laser measurement products tailored to these demands. The product line includes beam diagnostics cameras, thermopiles, pyroelectric sensors, and stand-alone meters like the LabMax Touch, which enable accurate analysis and data logging for energy and power measurements. Common sensors include MaxBlack ceramic-coated sensors for Ti:sapphire systems up to 1 kHz and diffuse metallic sensors for faster 10 kHz speeds, and spectrally calibrated optical diffusers for Nd:YAG lasers. For high-power lasers, the PM10K+ enables power measurement up to 12 kW. These tools provide the accuracy and reliability needed for comprehensive laser monitoring in fusion systems. 

High power and energy NIST traceable meters, with data and pulse analysis instrumentation.

Isolators: Our high-performing optical rotators and isolators are designed to meet the rigorous demands of fusion research, enabling scientists to achieve the extreme conditions necessary for nuclear fusion.  For the most demanding of applications, EOC has developed the PAVOS Ultra product line. These Potassium Terbium Fluoride (KTF) based isolators provide a generational improvement in performance. The thermal lens focal shift of the PAVOS Ultra is significantly reduced and slightly negative.  This means KTF is well suited for higher average power lasers while TGG (Terbium Gallium Garnet) is better suited higher energy.  When you combine KTF with high performing polarizers and heat management techniques you create an enabling product for the market.  We are committed to advancing fusion technology by providing cutting-edge laser components.

Standard and custom isolators offer large apertures, high power handling maintaining beam quality with significantly reduced thermal lensing.

Laser Amplifiers: Astrella femtosecond ultrafast CPA amplifiers are latest generation one-box kHz laser systems designed and produced for maximum reliability, up-time and industry-leading performance. A large number of these systems are implemented various scientific applications and industrial processes like fs materials processing.

It can be used as a reliable front-end for low-to-mid level high intensity laser facilities, though more typically provides <35 fs or <100 fs pulses for time-resolved and multidimensional coherent spectroscopy, THz spectroscopy, ultrafast electron diffraction, attosecond and high-harmonic generation experiments and EUV/soft X-ray spectroscopy.  With up to 9 mJ/pulse it is an ultimate choice for wide range of scientific applications. The unique design features, like sealed stretcher-compressor, hands-free oscillator and thermally-stabilized sub-systems have been optimized by HALT/HASS protocols providing reliability expected in industrial laser systems. It is an ideal source to pump an optical parametric amplifier to extend the wavelength coverage from UV to mid-IR.

Summary

In the highly specialized field of nuclear fusion research, we offer many of the key building blocks for beam delivery & focusing.  Every product category offers performance that can’t be matched by other manufacturers. Narrow linewidth high power QCW diode stacks, high precision large area optics & crystals, best in class mode maintaining isolators to cutting-edge gain fibers.

We have a history of successful collaborations with leading fusion research facilities, including the National Ignition Facility (NIF) and ITER. These partnerships underscore our ability to meet the stringent requirements of high-profile projects and contribute to significant advancements in the field.

Learn more about Coherent photonics products for laser fusion research.

Related Resources