8 ms·

Road map to clean energy using laser beam ignition of boron-hydrogen fusion

146 points by richardw 9y ago

deepnotderp 9y ago
Why not apply plasmonic nanoparticles for electromagnetic field enhancement via nanofocusing? (source: http://iopscience.iop.org/article/10.7567/JJAP.55.08RG01/pdf http://iopscience.iop.org/article/10.7567/JJAP.55.08RG01/pdf) I've seen this paper floating around for a while but not many attempts at experimental validation.
- amirhirsch 9y ago
  I’ve had an ongoing conversion with a few other people about using electromagnetic metamaterials for field enhancement and focusing in a plasma channel. We had previously worked on optical metamaterials for chemical sensing, and the idea for plasma enhancement was for considering staging and filtering methods for plasma wakefield accelerators in order to generate enough GeV for free electron lasing. The same idea could be used for proton acceleration for fusion. Possibly a concern is heat generated in the material by an accelerated plasma may be incompatible with passive coloumb-mode filtering. We had considered a target might be something like a disposable cartridge similar to other laser fusion designs. A very clever result in wakefield staging (out of the research labs) involves using a VHS tape for sacrificial optical coupling. The 10PW 1ps laser described in the parent post is not practical and would require similar staging methods.
- throwawayaway12 9y ago
  I have spotty wifi right now and can't read the actual paper at the moment (mainly a comment to remind myself to read this later). Quick thoughts from just reading the abstract: - There are very few facilities that do direct drive ICF (LLE in USA) -I am curious if the looked at hydro instabilities and preheating in this study
JumpCrisscross 9y ago
This is the process Tri-Alpha Energy [1] is working on. [1] https://en.m.wikipedia.org/wiki/Tri_Alpha_Energy,_Inc https://en.m.wikipedia.org/wiki/Tri_Alpha_Energy,_Inc.
- dnautics 9y ago
  It's the same nuclear reaction, but I doubt tri alpha is doing laser ignition.
kristianp 9y ago
Reminds me of Bussard's Polywell, their website doesn't seem to have been updated since 2014 though [1]. Bussard also wanted to do proton-boron fusion due to the same advantages mentioned. Edit: Apparently there has been progress, with a slideshow called "ready for commercialisation" presented this August by Jaeyoung Park [2][3]. [1] http://www.emc2fusion.org/ http://www.emc2fusion.org/ [2] http://www.talk-polywell.org/bb/viewtopic.php?f=10&t=6072&start=270 http://www.talk-polywell.org/bb/viewtopic.php?f=10&t=6072&st... [3] https://arpa-e.energy.gov/sites/default/files/5_PARK.pdf https://arpa-e.energy.gov/sites/default/files/5_PARK.pdf
- dnautics 9y ago
  The polywell at least has some sensible suggestions on how to capture the energy.
sandworm101 9y ago
Whenever I read about "ignition" my mind goes strait to weapons research. There is a blurred line between those looking wanting to use fusion for purposes of generating power, and those seeking to further nuclear weapons. 'Ignition' generally draws a good line between the two. For instance, the National Ignition Facility isn't doing reactor development. If I were the author, I'd reconsider the title to emphasize that it's focus is the generation of electrical power.
- saguro 9y ago
  Fusion technology of the kind being discussed here is not terribly useful for nuclear weapons. If you want nuclear weapons, build breeder fission reactors.
  - throwawayaway12 9y ago
    It is not for producing nuclear material, but for reproducing conditions relevant to weapons (although HBE itself may not be useful).
  - sandworm101 9y ago
    All fusion research has some relevance to weapons. If you are studying ignition, how to get fusion going, that is at the heart of research into building smaller thermonuclear devices. If you study containment, that is useful to increasing the efficiencies of weapons. Fire is fire.
    - krastanov 9y ago
      If we are going down that path of reasoning you can just as well say "all scientific research has some relevance to weapons". It also happens to have relevance to making life better, saving the planet, and understanding the universe.
    - petre 9y ago
      All energy discharges could be weaponized. Take the bow and arrow for instance.
jsjohnst 9y ago
> 10 petawatts laser for one picosecond > magnetic field plasma containment > produces 300KWh I’ll admit, while I’ve always been interested in lasers, I’m definitely below amateur level with them, but these requirements: 1) seems like its multiple orders of magnitude higher power than anything I’ve heard of in laser tech. Like 5-7 orders of magnitude. Is there research I’m unaware of here? 2) let’s assume for a second that the laser could be made, wouldn’t it require multiple orders of magnitude more power (as in 2-3 at least) to fire than what this reaction produces? 3) have we been able to contain plasma (as in super high energy plasma, not the stuff you see in novelty shops or older TV sets) for very long in a magnetic field? I thought the record was in number of seconds, certainly not long enough to be used for any continuous power production. Edit: Guess I was wrong on #1/2, had forgotten about this research[0] I’d read. [0] http://www.iflscience.com/technology/world-s-most-powerful-laser-2000-trillion-watts-what-s-it/ http://www.iflscience.com/technology/world-s-most-powerful-l...
- throwawayaway12 9y ago
  There are definitely petawatt class lasers currently (ex. the Texas petawatt). I think most are of order 100 fs.
  - jsjohnst 9y ago
    Per the research I just did, 2PW has been done for one picosecond, 10PW is being built. Apparently because of the very very short pulse, the energy required is trivially small (as in less than a light bulb in your house for an hour)
- jammaloo 9y ago
  10 petawatts for one picosecond is only a small amount of energy, about 0.002778 KWh http://www.wolframalpha.com/input/?i=10+petawatts+for+1+picosecond+in+kwh http://www.wolframalpha.com/input/?i=10+petawatts+for+1+pico...
- monochromatic 9y ago
  For a CW (continuous wave) laser, that would indeed be a lot of power. But for a q-switched pulsed laser, it’s not impossible.
deleted 9y ago
[deleted]
rfrey 9y ago
This asks for $35 to read the article, to save other non-academics the click.
- cinquemb 9y ago
  http://www.cambridge.org.https.sci-hub.tw/core/journals/laser-and-particle-beams/article/road-map-to-clean-energy-using-laser-beam-ignition-of-boronhydrogen-fusion/8BE057DC1BC9E0A588FB3ABAA993078C http://www.cambridge.org.https.sci-hub.tw/core/journals/lase...
sathackr 9y ago
> 14 milligram HB11 can produce 300 kWh energy That's an enormous amount of energy from a minuscule amount of mass. Using their predictions, I could run my house for a year on less than 1 gram of HB11. How does this compare with the energy output of current-day fission reactors?
- sathackr 9y ago
  To answer my own question, using numbers from [1]: U235 = 79,390,000 MJ/kg 1 kWh = 3.6MJ 1kg u235 = ~22,000,000kWh 1g u235 = ~22,000 kWh of energy For the HB11 reaction: 1000 / .014 = ~21,000 kWh/g So about the same as current fission. Except without the nasty byproducts. [1] https://www.quora.com/How-many-milligrams-of-uranium-is-needed-to-produce-one-googol-kilowatt-hours-of-electricity https://www.quora.com/How-many-milligrams-of-uranium-is-need... edit: complete failure of math.
- philipkglass 9y ago
  With mainstream present-day fission technology, it takes about 200 tonnes of natural mined uranium to fuel a 1000 MWe reactor for a year: http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/introduction/nuclear-fuel-cycle-overview.aspx http://www.world-nuclear.org/information-library/nuclear-fue... The same 300 kWh would then require about (300 / (1000 * 24 * 365 * 1000)) * (200000000) = 6.85 grams of natural uranium. Note that this is well below the theoretical energy density available from the fission of uranium. The main loss is because the naturally fissile isotope of uranium, U-235, is less than 1% of naturally occurring uranium. The much more common U-238 can be used completely in a breeder reactor, but there are currently only two operating breeder reactors in the world that generate electricity: https://en.wikipedia.org/wiki/BN-600_reactor https://en.wikipedia.org/wiki/BN-600_reactor https://en.wikipedia.org/wiki/BN-800_reactor https://en.wikipedia.org/wiki/BN-800_reactor
qume 9y ago
Dr. Emmett Brown: 10 petawatts! 10 petawatts. Great Scott! McFly: Wait - what the hell is a petawatt? Sorry couldn't resist.
Semiapies 9y ago
And ten years from now, someone will submit something, maybe also from Cambridge, saying we're really, really close to a breakthrough allowing clean fusion energy. They've been saying exactly this for longer than the 42 years I've been in this planet.
- Brotkrumen 9y ago
  Ever been involved in a project that constantly gets its funding cut? https://i1.wp.com/www.kickassfacts.com/wp-content/uploads/2016/04/FusionBudget.jpg https://i1.wp.com/www.kickassfacts.com/wp-content/uploads/20...
  - Semiapies 9y ago
    Sounds like an even finer reason not to make bullshit claims of breakthroughs coming any minute now for forty years.
- fpoling 9y ago
  The problem with fusion was that until recently it was extremely expensive to build experimental facilities with necessary parameters for meaningful progress. Nobody was ready for that. What happens recently is that due to technological improvement (powerful superconductive magnets, better simulations and faster controls) it is now possible to test things at regimes close to positive energy output on much smaller scales. So these days one can do useful investigation with 1e7 in funds, not 1e9. This is the reason for all various fusion startups. Now, it does not mean that we are going to have fusion soon, but at least it is now only 20 years from any moment, not 40.
  - Semiapies 9y ago
    The line has always been that fusion is twenty years away. In 2017, in 2007, in 1997, in 1987, and in 1977. It will be the same line in 2027.
exabrial 9y ago
"...a few kiloteslas..." This is a really cool paper and abstract. I had to giggle a bit at that line... I think the MRI machine I had images of of my knee was something like 6T?
ZenoArrow 9y ago
Here's another project that is working towards using boron-hydrogen fuel for nuclear fusion: https://lppfusion.com/ https://lppfusion.com/ Brief description of how the device works: https://lppfusion.com/fusion-power/dpf-device/ https://lppfusion.com/fusion-power/dpf-device/ To be clear, Dense Plasma Focus is the type of fusion device, and LPP Fusion is one of the teams researching them (there are others working with DPF devices). The following quote should help in understanding why it's an important project: http://m.digitaljournal.com/tech-and-science/technology/startup-lpp-fusion-s-device-exploits-instabilities-to-fuse-atoms/article/503354 http://m.digitaljournal.com/tech-and-science/technology/star... "“In the critical measure of how much energy out, we get per unit energy in, we’re No. 2 among all the experiments in the world,” Lerner says. “And we’re only one-third behind the JET [Joint European Torus] experiment in the United Kingdom—which has almost a thousand times our resources. In terms of results per unit dollar, we’re clearly No. 1, by a long way.”" They're running a crowdfunding campaign, if you're interested in investing in fusion energy: https://wefunder.com/lppfusion https://wefunder.com/lppfusion
tehabe 9y ago
"14 milligram HB11 can produce 300 kWh energy" – I guess it means thermal energy, how much of it can be used for electricity? What do I need for producing this? How small can be such a power plant be or how big must it be to be viable? Of course this could be all answered in the paper but it is a physics paper not a business or economics paper.
- Retric 9y ago
  Their is a wide range of thermal efficiency but something ~30% to 64% is possible. We can also use the heat directly in some applications making it useful number on it's own. Unfortunately making those pellets is fairly expensive an you only get 8$ or less worth of energy from them. Which is why the economics of this idea is simply terrible and the only value is for validation of H-bomb simulations.
  - DennisP 9y ago
    Since most of the energy output of boron fusion is in fast-moving charged particles, you aren't necessarily restricted to a thermal cycle. Focus fusion, for example, gets a pulse of alphas in a tight beam, which they can just aim through a coil for electricity. Tri Alpha also has plans for direct conversion, but I don't know how theirs works.
  - PaulAJ 9y ago
    But presumably if you are burning 10 of these every second the price is going to go down.
  - marcosdumay 9y ago
    > something ~30% to 64% is possible I would imagine that making those lasers go all the way into the fuel will restrict the operating temperature enough that those 30% will start to look too big. Can the lasers pass through windows without destroying them?
  - DennisP 9y ago
    How expensive? Do you have a source? From the papers I've seen by this group, they claim extremely good economics. The pellets for NIF were quite expensive but that's a very different technology.
nicodds 9y ago
The main advantage of this fusion reaction is that it is aneutronic, i.e. it doesn't produce any neutrons, so it is relatively safe. Petawatt class lasers are nowadays possible and several examples exists (Los Alamos, Oxford central laser facility, ELI Prague, South Korea). The technology used to compress photons energy in short length pulses is called "Chirped Pulse Amplification". This opened the way to femtosecond laser pulses.

146 points by richardw 9y ago

Why not apply plasmonic nanoparticles for electromagnetic field enhancement via nanofocusing? (source: http://iopscience.iop.org/article/10.7567/JJAP.55.08RG01/pdf http://iopscience.iop.org/article/10.7567/JJAP.55.08RG01/pdf) I've seen this paper floating around for a while but not many attempts at experimental validation.

amirhirsch 9y ago
I’ve had an ongoing conversion with a few other people about using electromagnetic metamaterials for field enhancement and focusing in a plasma channel. We had previously worked on optical metamaterials for chemical sensing, and the idea for plasma enhancement was for considering staging and filtering methods for plasma wakefield accelerators in order to generate enough GeV for free electron lasing. The same idea could be used for proton acceleration for fusion. Possibly a concern is heat generated in the material by an accelerated plasma may be incompatible with passive coloumb-mode filtering. We had considered a target might be something like a disposable cartridge similar to other laser fusion designs. A very clever result in wakefield staging (out of the research labs) involves using a VHS tape for sacrificial optical coupling. The 10PW 1ps laser described in the parent post is not practical and would require similar staging methods.
throwawayaway12 9y ago
I have spotty wifi right now and can't read the actual paper at the moment (mainly a comment to remind myself to read this later). Quick thoughts from just reading the abstract: - There are very few facilities that do direct drive ICF (LLE in USA) -I am curious if the looked at hydro instabilities and preheating in this study

JumpCrisscross 9y ago

This is the process Tri-Alpha Energy [1] is working on. [1] https://en.m.wikipedia.org/wiki/Tri_Alpha_Energy,_Inc https://en.m.wikipedia.org/wiki/Tri_Alpha_Energy,_Inc.

dnautics 9y ago
It's the same nuclear reaction, but I doubt tri alpha is doing laser ignition.

kristianp 9y ago

Reminds me of Bussard's Polywell, their website doesn't seem to have been updated since 2014 though [1]. Bussard also wanted to do proton-boron fusion due to the same advantages mentioned. Edit: Apparently there has been progress, with a slideshow called "ready for commercialisation" presented this August by Jaeyoung Park [2][3]. [1] http://www.emc2fusion.org/ http://www.emc2fusion.org/ [2] http://www.talk-polywell.org/bb/viewtopic.php?f=10&t=6072&start=270 http://www.talk-polywell.org/bb/viewtopic.php?f=10&t=6072&st... [3] https://arpa-e.energy.gov/sites/default/files/5_PARK.pdf https://arpa-e.energy.gov/sites/default/files/5_PARK.pdf

dnautics 9y ago
The polywell at least has some sensible suggestions on how to capture the energy.

sandworm101 9y ago

Whenever I read about "ignition" my mind goes strait to weapons research. There is a blurred line between those looking wanting to use fusion for purposes of generating power, and those seeking to further nuclear weapons. 'Ignition' generally draws a good line between the two. For instance, the National Ignition Facility isn't doing reactor development. If I were the author, I'd reconsider the title to emphasize that it's focus is the generation of electrical power.

saguro 9y ago
Fusion technology of the kind being discussed here is not terribly useful for nuclear weapons. If you want nuclear weapons, build breeder fission reactors.
- throwawayaway12 9y ago
  It is not for producing nuclear material, but for reproducing conditions relevant to weapons (although HBE itself may not be useful).
- sandworm101 9y ago
  All fusion research has some relevance to weapons. If you are studying ignition, how to get fusion going, that is at the heart of research into building smaller thermonuclear devices. If you study containment, that is useful to increasing the efficiencies of weapons. Fire is fire.
  - krastanov 9y ago
    If we are going down that path of reasoning you can just as well say "all scientific research has some relevance to weapons". It also happens to have relevance to making life better, saving the planet, and understanding the universe.
  - petre 9y ago
    All energy discharges could be weaponized. Take the bow and arrow for instance.

jsjohnst 9y ago

> 10 petawatts laser for one picosecond > magnetic field plasma containment > produces 300KWh I’ll admit, while I’ve always been interested in lasers, I’m definitely below amateur level with them, but these requirements: 1) seems like its multiple orders of magnitude higher power than anything I’ve heard of in laser tech. Like 5-7 orders of magnitude. Is there research I’m unaware of here? 2) let’s assume for a second that the laser could be made, wouldn’t it require multiple orders of magnitude more power (as in 2-3 at least) to fire than what this reaction produces? 3) have we been able to contain plasma (as in super high energy plasma, not the stuff you see in novelty shops or older TV sets) for very long in a magnetic field? I thought the record was in number of seconds, certainly not long enough to be used for any continuous power production. Edit: Guess I was wrong on #1/2, had forgotten about this research[0] I’d read. [0] http://www.iflscience.com/technology/world-s-most-powerful-laser-2000-trillion-watts-what-s-it/ http://www.iflscience.com/technology/world-s-most-powerful-l...

throwawayaway12 9y ago
There are definitely petawatt class lasers currently (ex. the Texas petawatt). I think most are of order 100 fs.
- jsjohnst 9y ago
  Per the research I just did, 2PW has been done for one picosecond, 10PW is being built. Apparently because of the very very short pulse, the energy required is trivially small (as in less than a light bulb in your house for an hour)
jammaloo 9y ago
10 petawatts for one picosecond is only a small amount of energy, about 0.002778 KWh http://www.wolframalpha.com/input/?i=10+petawatts+for+1+picosecond+in+kwh http://www.wolframalpha.com/input/?i=10+petawatts+for+1+pico...
monochromatic 9y ago
For a CW (continuous wave) laser, that would indeed be a lot of power. But for a q-switched pulsed laser, it’s not impossible.

deleted 9y ago

[deleted]

rfrey 9y ago

This asks for $35 to read the article, to save other non-academics the click.

cinquemb 9y ago
http://www.cambridge.org.https.sci-hub.tw/core/journals/laser-and-particle-beams/article/road-map-to-clean-energy-using-laser-beam-ignition-of-boronhydrogen-fusion/8BE057DC1BC9E0A588FB3ABAA993078C http://www.cambridge.org.https.sci-hub.tw/core/journals/lase...

sathackr 9y ago

> 14 milligram HB11 can produce 300 kWh energy That's an enormous amount of energy from a minuscule amount of mass. Using their predictions, I could run my house for a year on less than 1 gram of HB11. How does this compare with the energy output of current-day fission reactors?

sathackr 9y ago
To answer my own question, using numbers from [1]: U235 = 79,390,000 MJ/kg 1 kWh = 3.6MJ 1kg u235 = ~22,000,000kWh 1g u235 = ~22,000 kWh of energy For the HB11 reaction: 1000 / .014 = ~21,000 kWh/g So about the same as current fission. Except without the nasty byproducts. [1] https://www.quora.com/How-many-milligrams-of-uranium-is-needed-to-produce-one-googol-kilowatt-hours-of-electricity https://www.quora.com/How-many-milligrams-of-uranium-is-need... edit: complete failure of math.
philipkglass 9y ago
With mainstream present-day fission technology, it takes about 200 tonnes of natural mined uranium to fuel a 1000 MWe reactor for a year: http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/introduction/nuclear-fuel-cycle-overview.aspx http://www.world-nuclear.org/information-library/nuclear-fue... The same 300 kWh would then require about (300 / (1000 * 24 * 365 * 1000)) * (200000000) = 6.85 grams of natural uranium. Note that this is well below the theoretical energy density available from the fission of uranium. The main loss is because the naturally fissile isotope of uranium, U-235, is less than 1% of naturally occurring uranium. The much more common U-238 can be used completely in a breeder reactor, but there are currently only two operating breeder reactors in the world that generate electricity: https://en.wikipedia.org/wiki/BN-600_reactor https://en.wikipedia.org/wiki/BN-600_reactor https://en.wikipedia.org/wiki/BN-800_reactor https://en.wikipedia.org/wiki/BN-800_reactor

qume 9y ago

Dr. Emmett Brown: 10 petawatts! 10 petawatts. Great Scott! McFly: Wait - what the hell is a petawatt? Sorry couldn't resist.

Semiapies 9y ago

And ten years from now, someone will submit something, maybe also from Cambridge, saying we're really, really close to a breakthrough allowing clean fusion energy. They've been saying exactly this for longer than the 42 years I've been in this planet.

Brotkrumen 9y ago
Ever been involved in a project that constantly gets its funding cut? https://i1.wp.com/www.kickassfacts.com/wp-content/uploads/2016/04/FusionBudget.jpg https://i1.wp.com/www.kickassfacts.com/wp-content/uploads/20...
- Semiapies 9y ago
  Sounds like an even finer reason not to make bullshit claims of breakthroughs coming any minute now for forty years.
fpoling 9y ago
The problem with fusion was that until recently it was extremely expensive to build experimental facilities with necessary parameters for meaningful progress. Nobody was ready for that. What happens recently is that due to technological improvement (powerful superconductive magnets, better simulations and faster controls) it is now possible to test things at regimes close to positive energy output on much smaller scales. So these days one can do useful investigation with 1e7 in funds, not 1e9. This is the reason for all various fusion startups. Now, it does not mean that we are going to have fusion soon, but at least it is now only 20 years from any moment, not 40.
- Semiapies 9y ago
  The line has always been that fusion is twenty years away. In 2017, in 2007, in 1997, in 1987, and in 1977. It will be the same line in 2027.

exabrial 9y ago

"...a few kiloteslas..." This is a really cool paper and abstract. I had to giggle a bit at that line... I think the MRI machine I had images of of my knee was something like 6T?

ZenoArrow 9y ago

Here's another project that is working towards using boron-hydrogen fuel for nuclear fusion: https://lppfusion.com/ https://lppfusion.com/ Brief description of how the device works: https://lppfusion.com/fusion-power/dpf-device/ https://lppfusion.com/fusion-power/dpf-device/ To be clear, Dense Plasma Focus is the type of fusion device, and LPP Fusion is one of the teams researching them (there are others working with DPF devices). The following quote should help in understanding why it's an important project: http://m.digitaljournal.com/tech-and-science/technology/startup-lpp-fusion-s-device-exploits-instabilities-to-fuse-atoms/article/503354 http://m.digitaljournal.com/tech-and-science/technology/star... "“In the critical measure of how much energy out, we get per unit energy in, we’re No. 2 among all the experiments in the world,” Lerner says. “And we’re only one-third behind the JET [Joint European Torus] experiment in the United Kingdom—which has almost a thousand times our resources. In terms of results per unit dollar, we’re clearly No. 1, by a long way.”" They're running a crowdfunding campaign, if you're interested in investing in fusion energy: https://wefunder.com/lppfusion https://wefunder.com/lppfusion

tehabe 9y ago

"14 milligram HB11 can produce 300 kWh energy" – I guess it means thermal energy, how much of it can be used for electricity? What do I need for producing this? How small can be such a power plant be or how big must it be to be viable? Of course this could be all answered in the paper but it is a physics paper not a business or economics paper.

Retric 9y ago
Their is a wide range of thermal efficiency but something ~30% to 64% is possible. We can also use the heat directly in some applications making it useful number on it's own. Unfortunately making those pellets is fairly expensive an you only get 8$ or less worth of energy from them. Which is why the economics of this idea is simply terrible and the only value is for validation of H-bomb simulations.
- DennisP 9y ago
  Since most of the energy output of boron fusion is in fast-moving charged particles, you aren't necessarily restricted to a thermal cycle. Focus fusion, for example, gets a pulse of alphas in a tight beam, which they can just aim through a coil for electricity. Tri Alpha also has plans for direct conversion, but I don't know how theirs works.
- PaulAJ 9y ago
  But presumably if you are burning 10 of these every second the price is going to go down.
- marcosdumay 9y ago
  > something ~30% to 64% is possible I would imagine that making those lasers go all the way into the fuel will restrict the operating temperature enough that those 30% will start to look too big. Can the lasers pass through windows without destroying them?
- DennisP 9y ago
  How expensive? Do you have a source? From the papers I've seen by this group, they claim extremely good economics. The pellets for NIF were quite expensive but that's a very different technology.

nicodds 9y ago

The main advantage of this fusion reaction is that it is aneutronic, i.e. it doesn't produce any neutrons, so it is relatively safe. Petawatt class lasers are nowadays possible and several examples exists (Los Alamos, Oxford central laser facility, ELI Prague, South Korea). The technology used to compress photons energy in short length pulses is called "Chirped Pulse Amplification". This opened the way to femtosecond laser pulses.