There are different kinds of lasers. Last time I checked in 2018, Nd:glass lasers were the only choice for producing short, ultra-high power laser pulses with regular beam profile. Beam profile is very important for tight focusing. They may be 80's technology but these were produced in 2005. Efficient fiber optic lasers were already available but they are not suitable for the task. https://lasers.llnl.gov/about/how-nif-works/seven-wonders/la...

So the NIF spec'ed out a replacement using a diode-pumped Yb:SFAP laser that they estimated to be 10% efficient in ~2009:

https://en.wikipedia.org/wiki/Mercury_laser

https://www.laserfocusworld.com/test-measurement/research/ar...

The second link has more details, but they show a 0.7% efficient NIF vs. a 7% efficient Mercury laser in the tiny little chart graphic -- which would reduce the energy for this experiment from 285MJ to 28MJ. This is way outside my area of expertise, but from what I understand, the same general tech that LLNL used to generate the HAPLS for Europe's laser research could be applied to the Mercury-like lasers and increase efficiency even further.

https://www.techbriefs.com/component/content/article/tb/insi...

Thank you for interesting links. However, I see that the specified pulse energy of a single Mercury laser is 100J vs 18.7kJ for NIF so my point is still valid. There is no way to arrange 20k lasers all pointing at one pellet.

That was just a prototype laser to prove the direct drive approach with a high frequency solution.. They demo'ed a suitable laser operating at 10hz vs. 0.0001HZ with the existing NIF capability. Since the 100J Mercury laser was transferring more than 10x the energy to target compared to NIF (with an obvious path to 20x) - think of this as a 1/20th scale replacement for the a single NIF beam with the ability to fire multiple shots per second.

Can you point me to somewhere to read more about this? Also from wikipedia: "NIF hosts the world's most energetic laser."[0] Is that true and if so can many less powerful but more efficient lasers make up for it?

[0]https://en.wikipedia.org/wiki/National_Ignition_Facility#

So total energy consumed isn't what these places are optimizing for. LLNL/NIF "invented" a lot of this research so their facility is the least efficient but probably most important in the world. When they constructed their laser facility in 1996, NIF used the surest-bet laser system acknowledging that hypothetical competing systems could be better suited (solid state lasers were just coming into play at the time due to semiconductor manufacturing). They've done a massive amount of work ramp up the power and get their <0.5% system to ~0.7% efficient (power from the wall:power hitting the target). The NIF facility uses "indirect drive" where the energy from the lasers are first converted to xrays, and then the fuel is energized with the xrays. Not coincidentally, that's the exact mechanism that the Teller-Ulam nuclear warheads use to drive their fusion stage -- so NIF's selection here makes even more sense given their DOD funding.

Since a lot of modern laser research now overlaps with advanced semiconductor manufacturing, the competing systems are much more mature. Here's a good rundown, but experts think that it's plausible to use even up to 20% efficient systems. Rather than using the laser to first generate xrays - these "direct drive" systems deposit the energy from the lasers directly on the pellets.

https://physicstoday.scitation.org/do/10.1063/pt.6.2.2021102...