3 ms·

https://www.nature.com/articles/s41467-025-59675-5 https://www.nature.com/articles/s41467-025-59675-5 is the paper, claiming "~1.6 petahertz speed." That would

by kragen 1y ago

https://www.nature.com/articles/s41467-025-59675-5 https://www.nature.com/articles/s41467-025-59675-5 is the paper, claiming "~1.6 petahertz speed." That would be 190-nanometer wavelength, which is into the so-called "far ultraviolet" band of germicidal UVC, 6.6eV photon energy, on the edge of vacuum ultraviolet. And they're switching it with light. So, I wonder how long these devices will last if you keep using them? They say the light pulse is 6.5fs FWHM, so they weren't able to switch it on and off 1.6 quadrillion times per second; it's just that the transition from on (29nA) to off (<1nA) was only 630 attoseconds long, which is what they're describing as "petahertz". But "petahertz" implies a whole cycle time under a femtosecond, a cycle which would involve two transitions, which would presumably be 1.26 femtoseconds at this speed. (If they measured the speed of the off-to-on transition, I missed it skimming the paper.) And the actual light they're making the 6.5fs pulse out of is a "supercontinuum laser beam that spans over 400–1000 nm". That's still blue enough to raise some concerns about device longevity (though maybe graphene will prove tougher than certain other semiconductors which shall not be named here), but not to the same degree as if they were using actual petahertz light. I think the 2× exaggeration is sort of forgivable, and nothing else seems to be intentionally misleading, but it would still be easy to draw incorrect conclusions from the headline.

Aurornis 1y ago
I’m also confused about this. In EE it’s normal to use rise times to calculate bandwidth, but unless I’m missing something they didn’t do that correctly either. It would be such a strange mistake to occur on a paper about a topic of this caliber that I feel like I must be missing something.
- kragen 1y ago
  I suspect that maybe the rise time was much slower than the fall time, so it was the fall time they were excited about. But yeah, I'd think a 630-attosecond fall time represents 500–800 terahertz of bandwidth, not a petahertz or more.
kerblang 1y ago
For those playing subsecond bingo at home, wikipedia reference table https://en.wikipedia.org/wiki/Orders_of_magnitude_(time)#Less_than_one_second https://en.wikipedia.org/wiki/Orders_of_magnitude_(time)#Les...
gsf_emergency 1y ago
My read on the social context: they want to make a VUV/EUV solid state laser (for you-know-what). But they can't make any publishable headway in that direction, so they hype their results with the impressive sounding "petahertz" (terahertz desktop lasers at ambient conditions are mostly already in the bag) So, ask a trusted peer whether this is a something-burger or an attempted academic pivot. Since life is too short to spend on science you can't call your own: look at invites from ASML/TSMC/SMIC. That's what happened with Sn vapor lasers-- famously fickle things. The company that first got it to work properly (Cymer) isn't even on the relevant wikipedia page? And on the ASML they are associated with DUV? Really pushing the good faith here I think. I first paid attention thanks to interest from ASML. (Disclaimer: don't know any experimentalists working in the exact domain) E: sn vapor (laser-pumped) light source
- kragen 1y ago
  Hmm, why do you think that's what they were trying to do?
  - gsf_emergency 1y ago
    (This is not to say that ultrafast optical switching isn't far more exciting than desktop EUV sources-- in fact, I personally applaud the pivot, if indeed there was one ) I believe I recently saw on goog schol other attempts at vuv lasing/light emission using very similar setup of laser pumping in si-gr (Can't remember the exact search terms I used at the time, or how unsuccessful they were) E: here's one (2019 dissertation; ndyag ns-pulsed laser probe) which openly states the underlying motivations. You can also check the phd thesis when it comes out, usually they won't hold back on their informal motivations at defence-time :) https://tesidottorato.depositolegale.it/bitstream/20.500.14242/109945/1/Malik_Nadeem_Ahmed_Thesis.pdf https://tesidottorato.depositolegale.it/bitstream/20.500.142... If I hadn't read your doubts about the stability above, which reminded me of the limited lifetime of sn vapor sources (there due to contamination of optics), I wouldn't have imputed those motivations to TFA E2: one from 2019 on VdW vuv detectors (ns response time) https://pubs.acs.org/doi/full/10.1021/acsphotonics.9b00729 https://pubs.acs.org/doi/full/10.1021/acsphotonics.9b00729 E3: I also thought that the mention of "ambient conditions" in the uni PR was slightly out of place outside the context of light sources.

by kragen 1y ago

Aurornis 1y ago

I’m also confused about this. In EE it’s normal to use rise times to calculate bandwidth, but unless I’m missing something they didn’t do that correctly either. It would be such a strange mistake to occur on a paper about a topic of this caliber that I feel like I must be missing something.

kragen 1y ago
I suspect that maybe the rise time was much slower than the fall time, so it was the fall time they were excited about. But yeah, I'd think a 630-attosecond fall time represents 500–800 terahertz of bandwidth, not a petahertz or more.

kerblang 1y ago

For those playing subsecond bingo at home, wikipedia reference table https://en.wikipedia.org/wiki/Orders_of_magnitude_(time)#Less_than_one_second https://en.wikipedia.org/wiki/Orders_of_magnitude_(time)#Les...

gsf_emergency 1y ago

My read on the social context: they want to make a VUV/EUV solid state laser (for you-know-what). But they can't make any publishable headway in that direction, so they hype their results with the impressive sounding "petahertz" (terahertz desktop lasers at ambient conditions are mostly already in the bag) So, ask a trusted peer whether this is a something-burger or an attempted academic pivot. Since life is too short to spend on science you can't call your own: look at invites from ASML/TSMC/SMIC. That's what happened with Sn vapor lasers-- famously fickle things. The company that first got it to work properly (Cymer) isn't even on the relevant wikipedia page? And on the ASML they are associated with DUV? Really pushing the good faith here I think. I first paid attention thanks to interest from ASML. (Disclaimer: don't know any experimentalists working in the exact domain) E: sn vapor (laser-pumped) light source

kragen 1y ago
Hmm, why do you think that's what they were trying to do?
- gsf_emergency 1y ago
  (This is not to say that ultrafast optical switching isn't far more exciting than desktop EUV sources-- in fact, I personally applaud the pivot, if indeed there was one ) I believe I recently saw on goog schol other attempts at vuv lasing/light emission using very similar setup of laser pumping in si-gr (Can't remember the exact search terms I used at the time, or how unsuccessful they were) E: here's one (2019 dissertation; ndyag ns-pulsed laser probe) which openly states the underlying motivations. You can also check the phd thesis when it comes out, usually they won't hold back on their informal motivations at defence-time :) https://tesidottorato.depositolegale.it/bitstream/20.500.14242/109945/1/Malik_Nadeem_Ahmed_Thesis.pdf https://tesidottorato.depositolegale.it/bitstream/20.500.142... If I hadn't read your doubts about the stability above, which reminded me of the limited lifetime of sn vapor sources (there due to contamination of optics), I wouldn't have imputed those motivations to TFA E2: one from 2019 on VdW vuv detectors (ns response time) https://pubs.acs.org/doi/full/10.1021/acsphotonics.9b00729 https://pubs.acs.org/doi/full/10.1021/acsphotonics.9b00729 E3: I also thought that the mention of "ambient conditions" in the uni PR was slightly out of place outside the context of light sources.