Optics Recycle Loop

Summary

Big Ideas Lab: Optics Recycle Loop

Episode Overview

In the February 18, 2025 episode of Big Ideas Lab, hosted by Mission.org, listeners are taken deep inside the Lawrence Livermore National Laboratory (LLNL) to explore the intricate and innovative process known as the Optics Recycle Loop. This episode delves into how scientists and engineers at the National Ignition Facility (NIF) tackle the formidable challenges of maintaining and optimizing one of the world’s most powerful laser systems. Through engaging discussions, expert insights, and detailed explanations, the episode highlights the precision, ingenuity, and relentless pursuit of excellence that drive groundbreaking advancements in fusion energy and national security.

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1. The Scale and Precision of NIF

The episode opens with a vivid analogy comparing the NIF’s complexity to a Formula One race car pit stop, emphasizing the necessity for flawless performance under extreme conditions.

Narrator [00:02]: “...imagine this level of precision on a cosmic scale. Inside the National Ignition Facility at Lawrence Livermore National Laboratory, 192 laser beams work together, harnessing immense power to replicate the energy of the stars.”

NIF’s mission is to achieve fusion ignition by replicating the extreme conditions found in stellar cores, making it the most energetic and precise laser system on the planet. Since its inception in 2009, NIF has been pivotal in advancing national security and high-energy density physics, ensuring the safety and reliability of America’s nuclear arsenal without the need for underground testing.

2. The Challenge of Optics Damage

Operating NIF involves directing 192 laser beams through a complex array of over 7,000 large optics. These optics, critical for amplifying and directing the laser energy, are subjected to extreme intensities that can cause microscopic damage.

Tayyeb Suratwalla [06:38]: “The purpose of an optic is to manipulate the light that is transitioning through it.”

As NIF fires, even the smallest imperfections—cracks and pits as minute as 1/20th the diameter of a human hair—can form on the optics. Laura Masio Kegelmaier, who leads the optics inspection and data management team, explains the severity of this issue:

Laura Masio Kegelmaier [08:09]: “NIF was designed and built to shoot laser light at energies that we knew would damage the optics. The laser light actually puts little pits of damage in the glass that we use for... getting the laser light from where it starts to where it hits the target.”

3. Developing the Optics Recycle Loop

To address the inevitable damage, LLNL engineers devised the Optics Recycle Loop, a sophisticated system designed to repair and reuse damaged optics efficiently.

Laura Masio Kegelmaier [09:54]: “When the laser was being designed and built... we can swap your optic by taking out one module and replacing it.”

Key Components of the Recycle Loop:

• Modular Design: Optics are housed in removable modules, allowing for quick and contamination-free exchanges.

• Advanced Diagnostics: Real-time monitoring using high-resolution cameras detects damage as small as 50 microns, ensuring precise identification and timely intervention.

• Repair Process: Damaged optics are meticulously repaired using tools like the CO₂ laser, which performs precise “laser surgery” to remove damaged sites, leaving behind minimal divots that slightly scatter light without significantly impacting performance.

Ren Carr, the science and technology leader for the optical and material science group, provides a deeper scientific perspective:

Ren Carr [18:20]: “When you look at the damage sites... you see molten regions, you see fibers of previously molten glass... it's really very an interesting set of physical phenomena.”

4. The Repair Workflow

The repair workflow is a seamless process ensuring NIF’s continuous operation:

1. Damage Detection: After several NIF shots, cameras capture high-resolution images to identify damage on the optics.

2. Damage Mapping: Advanced AI software processes these images to generate detailed maps of each optic, pinpointing areas that require attention.

3. Laser Surgery: The identified damage sites are precisely targeted and repaired using CO₂ lasers, effectively removing defects while maintaining the integrity of the optic.

4. Optic Reinstallation: Repaired optics are returned to service, enabling NIF to maintain its rigorous firing schedule without significant interruptions.

Tayyeb Suratwalla [14:24]: “For the Optics Recycle Loop... the cumulative power and energy that they shoot is strongly linked to the rate at which we can recycle the components and return them back to the facility.”

5. Addressing Unique Challenges: The Bottom Beams

Despite the efficacy of the recycle loop, certain beams—specifically the bottom 32 beams—present unique challenges due to gravity, leading to the accumulation of debris that compromises optic integrity.

Ren Carr [19:55]: “We now have 128 beams that permanently have these fusicle debris shields in... but we've found additional problems in the bottom 32 beams of NIF.”

Instead of abandoning these beams, the team innovatively repurposed them as composting beams, allowing them to continue functioning until the optics can no longer be repaired.

Ren Carr [20:57]: “We have turned the bottom 16 beams of NIF to our composting beams... we just let them damage.”

This strategy maximizes the lifespan of optics and provides valuable data for future innovations, exemplifying LLNL’s resourcefulness and commitment to continuous improvement.

6. The Continuous Cycle of Innovation

As NIF pushes towards higher energies and more frequent shots, new damage mechanisms emerge, necessitating ongoing advancements in optic materials and repair techniques. The Optics Recycle Loop exemplifies a dynamic interplay between operational demands and engineering solutions, ensuring that NIF remains at the forefront of fusion research.

Ren Carr [18:14]: “Damage for the laser, it's just a big nuisance, but scientifically, it's just fascinating.”

7. A Hub for Talent and Innovation

Throughout the episode, LLNL emphasizes its role as a hub for cutting-edge science and technology, inviting professionals from diverse fields to contribute to its mission. With 139 open positions spanning science, engineering, IT, administration, and skilled trades, LLNL underscores the collaborative and innovative environment that drives its success.

Tayyeb Suratwalla [14:24]: “We call it a currency, which is termed log growth, which describes the rate at which we can shoot NIF.”

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Conclusion

The Big Ideas Lab episode on the Optics Recycle Loop provides an in-depth look into the meticulous and innovative processes that sustain the National Ignition Facility’s operations. Through expert interviews and detailed explanations, listeners gain a comprehensive understanding of how LLNL addresses the formidable challenges of high-energy laser systems. The episode not only highlights the technical prowess and ingenuity of the LLNL team but also showcases the institution’s commitment to fostering talent and pushing the boundaries of scientific discovery.

For those inspired by the innovations at LLNL and interested in contributing to groundbreaking work, the episode concludes with an invitation to explore career opportunities at llnl.gov/careers, emphasizing the laboratory’s dedication to collaboration, professional growth, and impactful work.

Notable Quotes:

• Tayyeb Suratwalla [06:38]: “The purpose of an optic is to manipulate the light that is transitioning through it.”

• Laura Masio Kegelmaier [08:09]: “NIF was designed and built to shoot laser light at energies that we knew would damage the optics.”

• Ren Carr [18:20]: “When you look at the damage sites... it's really very an interesting set of physical phenomena.”

• Tayyeb Suratwalla [14:24]: “We call it a currency, which is termed log growth, which describes the rate at which we can shoot NIF.”

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This comprehensive exploration of the Optics Recycle Loop underscores LLNL’s pivotal role in advancing fusion technology and maintaining national security, all while fostering an environment of relentless innovation and excellence.

Transcript

[Narrator]

A Formula One race car hurtles down the track at blistering speeds. Every second counts, and every part of the car must perform flawlessly. But over time, tires can wear thin, engines strain and components face extreme heat and pressure. When the car pulls into the pit stop, a precisely coordinated team springs into action. In a matter of seconds, they replace worn parts, make adjustments, and send the car back to the race ready to perform at its maximum potential. Now imagine this level of precision on a cosmic scale. Inside the National Ignition Facility at Lawrence Livermore National Laboratory, 192 laser beams work together, harnessing immense power to replicate the energy of the stars. And like a Formula One car, the system faces constant challenges. Tiny cracks and pits as small as 1 20th the diameter of a human hair can form on the optics due to laser induced damage every time NIF fires. These imperfections, if left unchecked, can grow exponentially, thus scattering light, reducing efficiency and jeopardizing the entire laser system. Fortunately, scientists and engineers at Lawrence Livermore National Laboratory have developed solutions to these challenges. Today we're exploring exploring the optics recycle loop, a cutting edge process akin to a high tech pit stop where damaged components are repaired and returned to service with precision. We'll meet the researchers solving the mysteries of laser damage, the engineers designing innovative tools, and the technology supporting it all. Welcome to the Big Ideas Lab. Your weekly exploration inside Lawrence Livermore National Laboratory. Hear untold stories, meet boundary pushing pioneers, and get unparalleled access inside the gates. From national security challenges to computing revolutions, discover the innovations that are shaping tomorrow. Today, Lawrence Livermore National Laboratory is opening its doors to a new wave of talent. If you're driven by curiosity and a desire to solve complex challenges, the lab has a job opening for you. Currently, there are 139 open positions. These include opportunities in science, engineering, business administration, and the skilled trades. From enhancing national security to pioneering new energy sources and advancing scientific frontiers, Lawrence Livermore National Laboratory is where you can make your mark on the world. Today's Open roles lead power grid engineer, laser modeling physicist, postdoctoral researcher, OCEC program leader and chief data architect. But the list doesn't end there. Explore all available positions at llnl. Each opportunity comes with a comprehensive benefits package tailored to your lifestyle and future. Join a workplace that champions professional growth, fosters collaboration, inspires innovation, and drives the pursuit of excellence. If you are ready to contribute to work that matters, visit llnl.govcareers to explore all the current job listings. That's LLNL. Your expertise could very well be the highlight of our next podcast Interview. Don't wait. Lawrence Livermore National Laboratory's national ignition Facility, or NIF, began operations in 2009. Its mission is to replicate the extreme conditions where fusion ignition naturally occurs, such as in the cores of stars. NIF is the most energetic and precise laser system on the planet. It pushes the boundaries of science and technology, generating temperatures of 100 million degrees and pressures more than 100 billion times Earth's atmosphere. This unique facility plays a critical role in advancing national security and high energy density physics. By conducting experiments that ensure America's nuclear arsenal remains safe, secure, and reliable without the need for underground testing. NIF provides essential data to modernize and uphold our defense systems. But beyond its earthbound contributions, NIF opens a window into the cosmos. By replicating the extreme states of matter found in the center of planets, stars, and other celestial objects, NIF helps scientists unlock the mysteries of the universe. In December 2022, Lawrence Livermore National Laboratory made history by demonstrating fusion ignition for the first time ever in a laboratory setting. For the smallest fraction of a second, they replicated a star on Earth. And they've repeated this achievement over and over and over. As we've explained in previous episodes, fusion ignition is the process where two atomic nuclei combine to form a single heavier nucleus. This releases an immense amount of energy. At the National Ignition Facility, scientists are turning this cosmic phenomenon into a groundbreaking reality. Each of NIF's 192 laser beams, roughly 40 centimeters in size, travel nearly a kilometer through the facility. Along the way, they pass through more than 7,000 large optics that amplify, transmit, reflect, shift wavelengths, or focus the light. All of this precision engineering converges energy from the lasers onto a tiny fuel pellet, compressing it to extreme temperatures and pressures.

[Tayyeb Suratwalla]

The purpose of an optic is to manipulate the light that is transitioning through it.

[Narrator]

Tayyeb Suratwalla is the program director for optics and material science at Lawrence Livermore.

[Tayyeb Suratwalla]

So either you're trying to reflect it, you're trying to focus it, you're trying to use it, where you increase the intensity of the light.

[Narrator]

The NIF spans three football fields housing a labyrinth of machinery, precision optics, and advanced systems.

[Tayyeb Suratwalla]

NIF is going in a new paradigm space in terms of operations of lasers. The real important question is why? Why are these lasers so large? And the reason is that there is a limitation today of how much light you can put through a material before you will destroy it. And because that limitations, we have to make bigger optics and try to look at strategies to get more and more light through those components.

[Narrator]

The immense scale of NIF's lasers is crucial for achieving the conditions necessary for fusion. However, this extraordinary combination of power and energy pushes the optics to their absolute limits, leading to potential damage. When light interacts with delicate glass components, Laser beam intensity is so extreme that the light can physically remove material from the surface of the glass. Optics carving away microscopic layers with each pulse. Laura Masio Kegelmaier led the team at NIF for optics inspection and data management.

[Laura Masio Kegelmaier]

NIF was designed and built to shoot laser light at energies that we knew would damage the optics. If you think of an optic as a piece of glass and damage as what happens if a rock hits your windshield, you get a pit of damage to that glass. And it's hard to imagine that laser light does the same thing as a rock, but it is so intense that the laser light actually puts little pits of damage in the glass that we use for many purposes to get the laser light from where it starts to where it hits the target.

[Narrator]

The nifs optics are made from various types of glass.

[Laura Masio Kegelmaier]

We have crystals. People know what crystals are because you could put a crystal in your window and see all the different colors come through. We have amplifiers. You put in a certain amount of light energy, and more light energy is going to come out of an amplifier. Our amplifier glass is made out of a very special material that accepts light from an ordinary flash lamp, like your camera flash, and it donates that light to the laser, and that's how it gives the laser more energy. So when our laser starts out is a very weak pulse of light, like a laser pointer, that you would shine. It starts out weaker than a laser pointer, but by the time it goes through amplifiers, it has so much energy that after we change the color of the light, it can damage the optics that are the most expensive optics in the whole system. So we don't want to just let our optics damage and then throw them out.

[Narrator]

Because of the high costs associated with these optics, the lab developed what's known as the optics recycle loop, A carefully designed system to efficiently repair and reuse the laser's most delicate components.

[Laura Masio Kegelmaier]

When the laser was being designed and built, if you just build your tunnel solid, but you have a bunch of pieces of glass inside your tunnel, it's going to be really hard to replace those pieces of glass. But if you build your tunnel with little modules that come in and out from the side, then you can swap your optic by taking out one module and replacing it. So these beam lines were designed with line removable units, which a clean room robot can Slide one out without adding any debris or contamination in a very clean manner. Slide another one in. We take the one that came out, and we repair it. It goes through the recycle loop, and then again, it's ready to be exchanged online with another one. So we had to design the laser with this concept in mind so that the optics could be exchanged and repaired and reused. People didn't know exactly if this was possible, and we didn't know exactly all the details of how it would work, but they built the laser to allow for these exchanges.

[Narrator]

These removable units allow for seamless optic exchanges, ensuring that maintenance can be done without risking contamination. And the ingenuity didn't stop there. NIF was also equipped with advanced diagnostic systems and cameras to monitor the optics in real time, adding another layer of precision to its operations.

[Laura Masio Kegelmaier]

We find every single pit of damage using cameras when the optics are in this gigantic laser facility. And then those camera systems and the software that we've worked on for decades lets us know exactly where every damage site is, so we know when to remove an optic so we can repair all the damage and we can put it back to work and extend the usability of that optic. We can use it many, many times with this recycle loop concept.

[Narrator]

To meet the demanding firing schedule, roughly every day, damaged optics are removed and replaced with a freshly refurbished set while the originals are repaired. This exchange allows NIF experiments to continue uninterrupted without delays caused by the intricate repair process.

[Laura Masio Kegelmaier]

The laser is firing at higher and higher energy, so the damage is changing its nature. The optics are suffering in different ways, and it's always a tug of war because, of course, the people doing the ignition experiments want to just hit the target with more energy. And the people protecting the optics are saying, well, wait, can we hold back? And so we're constantly making the optics tougher.

[Narrator]

So how does the repair and recycle process work, and why is it critical to NIF's operations? Lawrence Livermore National Laboratory invites you to join a diverse team of professionals. The lab is currently hiring a lead power grid engineer, a laser modeling physicist, postdoctoral researcher, an OCEC program leader, a chief data architect, and 139 other positions for scientists, engineers, IT experts, administrative and business professionals, welders, and more. At Lawrence Livermore National Laboratory, your contributions are not just jobs. They're a chance to make an impact. From strengthening US Security to leading the charge in revolutionary energy solutions and expanding the boundaries of scientific knowledge, the lab values collaboration, innovation, and excellence, offering a supportive workspace and comprehensive benefits to ensure your well being and secure your future. Seize the opportunity to help solve something monumental. Dive into the wide variety of job [e-mail] careers. This is your chance to join a team dedicated to a mission that matters. That's llnl.govcareers. your expertise might just be the spotlight in our next podcast interview. Don't delay.

[Tayyeb Suratwalla]

For the Optics Recycle Loop the basic concept is we're going to pull the optic off. We're going to repair the damage site and return it. The ability for the NIF to operate at a certain rate, how many shots that they take, the cumulative power and energy that they shoot is strongly linked to the rate at which we can recycle the components and return them back to the facility. So there's this rate balance. In fact, we made up our own terminology. We call it a currency, which is termed log growth, which describes the rate at which we can shoot nif.

[Narrator]

The recycle rate depends on the shot rate or log growth and continued improvements in the laser damage resistance of the optics. Optics improvements enable higher energy and power or a higher shot rate. After every few NIF shots, a special camera system captures high resolution images of the optic components near the target area. These cameras can detect damage as small as 50 microns. This allows scientists to pinpoint exactly where damage is occurring on each optic. Because NIF fires almost daily, it's not practical to immediately remove an optic every time damage is detected. Instead, the team uses a unique technique. They place a shadow over the damaged area in the beam. Imagine a very small umbrella placed in the pathway of the laser beam to cast a small shadow over the damaged spot to protect it from further harm. By eliminating the energy in that area, it prevents the damage from spreading.

[Tayyeb Suratwalla]

That damage site won't get bigger and bigger. It's like a protection mechanism. Every time we do that, we're turning the beam into kind of Swiss cheese, right? Because you're putting all these little black spots all over it. So there's a limit to the number of those that we can apply.

[Narrator]

When it's time to remove an optic, the component is carefully extracted from the system. The optic is transported to a clean room facility where it undergoes an intricate repair process. Scientists first inspect and clean the optic to avoid contamination. Next, they place it under an OTOM animated microscope, which catalogs all the optics features. The level of detail is astounding. Each optic is scanned with magnification so precise that even features as small as 5 to 10 microns are documented. This requires up to 20,000 images per optic advanced AI software processes these images, sorting through thousands, thousands of features, damaged sites, debris, scratches, and other minor imperfections, and generating a detailed map of the optic containing every flaw. Most are benign, but those requiring repair are sent to the next stage.

[Tayyeb Suratwalla]

We use another laser. This is called the CO2 laser, or carbon dioxide laser. And we shoot the optic at the position where that damage site is, and we essentially do laser surgery at that location. And we remove the damage site. And what we leave behind is a tiny little divot on the surface of that optic. And we do this on essentially all the damage sites that get created on these optics. And the repair rate is on the order of about 10 to 20,000 sites per month.

[Narrator]

But what about the tiny little divot that's left after the repair?

[Tayyeb Suratwalla]

What it does is it basically scatters the light a little bit, and it's not that problematic. There's a limit to the number of these divots you can put onto a part. And at that point, once it gets to a certain level, which represents about 1% of the beam area, we retire the optic.

[Narrator]

Here's Ren Carr.

[Ren Carr]

I'm here for laser damage.

[Narrator]

He's the science and technology leader for the optical and material science and technology group at the lab.

[Ren Carr]

When you look at the damage sites, after everything has settled down, you see molten regions, you see fibers of previously molten glass that have sprayed all over the place, and big fractures. It's really very an interesting set of physical phenomena that occur every time you get a laser. Damage for the laser, it's just a big nuisance, but scientifically, it's just fascinating.

[Narrator]

These damaged sites might appear as tiny sparkles on the surface of the optic, but under an electron microscope, the heat and energy create molten cores surrounded by intricate fractures, each telling the story of the laser's immense power.

[Ren Carr]

From standing three feet away and looking at an optic, you just see a tiny little sparkly thing. But with an electron microscope, you see all these different details about it, the previously molten core and the fracture that surrounds it. Our damage heights grow exponentially. If you shoot 10 shots on the NIF, the damage site, that might start out as a 10th of a human hair on the first shot. It could be 100 human hair diameter by the 10th shot, and it just grows more and more quickly. We have found ways to repair these damaged sites, but only if we don't let them get too big. They start small and they grow and they grow and they grow. But because it's an exponential growth, the rate at which they get bigger speeds up as they grow.

[Narrator]

However, not all damaged optics can be fixed. Some optics reach a point where repair is no longer possible, and their role in the system shifts. This is especially true for the bottom beams at NIF, where gravity introduces unique challenges.

[Ren Carr]

We now have 128 beams that permanently have these fusicle debris shields in, and they're protecting the grading debris shield. We have found additional problems in the bottom 32 beams of NIF. And what happens is you blow the target up and you get damage on these other things, and then gravity just pulls it down to the bottom.

[Narrator]

This accumulation of debris in the bottom beams creates what the team jokingly calls the ashtray of nif.

[Ren Carr]

All the gunk from blowing the targets up and all the damage from all the other optics, it just finds its way down and just kind of rattles down and gets around the fused silica debris shield. And so when we did an experiment where we put the fused silica debris shield in the bottom 16 beams of NIF, it helped, but it didn't help enough for the cost of them. So we've punted on that.

[Narrator]

Rather than abandon these beams entirely, the team found a creative solution turning them into composting beams.

[Ren Carr]

We have turned the bottom 16 beams of NIF to our composting beams. And by what I mean by that is when we've pretty much used up our optics on the other beams, they don't damage as fast now because of the protections we've given them, but eventually they just kind of run out of life. And so the last time we think we're going to be able to install them, we put them in the bottom 16 beams. We know we're not going to be able to repair these no matter what, and so we put them down there. We just let them damage.

[Narrator]

This resourceful approach maximizes the lifespan of optics and provides valuable data for future innovations. Once they've extracted every last bit of life out of an optic, it must be replaced. The bottom beams remind us that even the toughest obstacles can yield opportunities for discovery and adaptation. As the team continues to make optics improvements, and as NIF goes to higher energies, new damage mechanisms will emerge. As the saying goes, the reward for for good work is more work. This cycle continues to push NIF to operate at higher and higher energy levels. Like every pit stop in a Formula One race demands perfect timing and coordination. Every repair and innovation at NIF ensures the laser system performs at its peak. From designing a facility ready for the future to restoring optics damaged by the world's most energetic laser, each challenge sets the stage for the Next Leap in Innovation Lawrence Livermore National Laboratory is opening its doors to a new wave of talent. Whether you're a scientist, an IT professional, a welder, an advanced administrative or business professional, or an engineer, Lawrence Livermore National Laboratory has an opportunity for you. From enhancing national security to pioneering new energy sources and advancing scientific frontiers, Lawrence Livermore National Laboratory is where you can make your mark on the world. Lawrence Livermore National Laboratory's culture is rooted in collaboration, innovation and the pursuit of excellence. We offer a work environment that supports your professional growth and a benefits package that looks after your well being and future. Are you ready to contribute to work that matters? Visit llnl.govcareers to explore current job openings and learn more about the application process. Don't miss the chance to be a part of a mission driven team working on projects that make the impossible possible. Visit llnl.govcareers now to view the current job listings. Remember, that's llnl.govcareers your expertise could be the highlight of our next podcast interview. Don't wait, explore the possibilities today. Thank you for tuning in to Big Ideas Lab. If you loved what you heard, please let us know by leaving a rating and review. And if you haven't already, don't forget to hit the Follow or Subscribe button in your podcast app to keep up with our latest episode. Thanks for listening.