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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 r

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/laser-glass https://lasers.llnl.gov/about/how-nif-works/seven-wonders/la...

mikeyouse 4y ago
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://en.wikipedia.org/wiki/Mercury_laser https://www.laserfocusworld.com/test-measurement/research/article/16551380/highpower-solidstate-lasers-the-mercury-laser-moves-toward-practical-laser-fusion 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/insiders/pit/stories/45252 https://www.techbriefs.com/component/content/article/tb/insi...
- corille 4y ago
  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.
  - mikeyouse 4y ago
    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 a single NIF beam with the ability to fire multiple shots per second. Even if they couldn't increase the power past 100J (which they certainly can), using 2,000 beams instead of 192 doesn't seem too difficult given the much smaller overall energy and heat-removal requirements.

mikeyouse 4y ago

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://en.wikipedia.org/wiki/Mercury_laser https://www.laserfocusworld.com/test-measurement/research/article/16551380/highpower-solidstate-lasers-the-mercury-laser-moves-toward-practical-laser-fusion 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/insiders/pit/stories/45252 https://www.techbriefs.com/component/content/article/tb/insi...

corille 4y ago
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.
- mikeyouse 4y ago
  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 a single NIF beam with the ability to fire multiple shots per second. Even if they couldn't increase the power past 100J (which they certainly can), using 2,000 beams instead of 192 doesn't seem too difficult given the much smaller overall energy and heat-removal requirements.