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Space Science

Photonic Laser Thruster Promises Earth to Mars in a Week 413

Posted by CowboyNeal
from the buckle-up dept.
serutan writes "Using lasers to drive spaceships has been a subject of interest for many years, but making a photonic engine powerful enough for practical use has been elusive. Dr. Young Bae, a California physicist, has built a demonstration photonic laser thruster that produces enough thrust to micro-maneuver a satellite. This would be useful in high-precision formation flying, such as using a fleet of satellites to form a space telescope with a large virtual aperture. Scaled up, a similar engine could speed a spacecraft to Mars in less than a week."
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Photonic Laser Thruster Promises Earth to Mars in a Week

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  • by Harmonious Botch (921977) * on Friday September 14, 2007 @12:20AM (#20599273) Homepage Journal
    ...we fried it duing liftoff.
    • acceleration? (Score:5, Insightful)

      by OrangeTide (124937) on Friday September 14, 2007 @12:22AM (#20599283) Homepage Journal
      What sort of acceleration would that be? Would it be multi G-force worth, that might be impractical for humans.
      • by scoot80 (1017822) on Friday September 14, 2007 @12:32AM (#20599353) Journal
        They didn't say you would get there alive. They just said you would get there in a week.
        • Re:acceleration? (Score:5, Informative)

          by Harmonious Botch (921977) * on Friday September 14, 2007 @01:08AM (#20599609) Homepage Journal
          About 1/2 G.
          • Re:acceleration? (Score:5, Informative)

            by Score Whore (32328) on Friday September 14, 2007 @02:00AM (#20599881)
            Half a G will get you way further than Mars in a week. The greatest distance between Earth and Mars is 391 million Km. Assuming you're going to go constant acceleration half way and constant acceleration in the other direction the second half of the trip, 1/2 G acceleration will get you 897 million Km end to end in seven days.

            If you don't mind going through the Sun, that 1/2 G will get you Earth to Jupiter, in the worst geometry possible, in seven days and one hour and thirty minutes.
            • Re:acceleration? (Score:5, Informative)

              by demonlapin (527802) on Friday September 14, 2007 @03:39AM (#20600337) Homepage Journal
              No, that only works if you're accelerating in the same direction at 1/2G the whole time. If you want to end up in the right place with zero speed, you need:

              s = 0.5at^2

              s = 0.5 * 4.9 * (3.5d * 24h/d * 3600s/hr)^2

              = 224 042 112 000 m, a bit over 224 million km
              Then double it, since you'll go just as far in the deceleration, and you get 448 million km, not 897.
              • Re: (Score:3, Interesting)

                by ZOmegaZ (687142)
                If .5G could get you to your turnaround point in 3.5 days, that would mean you'd be going about 1500 km/s when you get there. That's equivalent to 1e6 MJ/kg, or 3.6 MW/kg. Sayth the Wiki [wikipedia.org] that a nuclear fission plant can provide that kind of energy density, and to spare. Not sure about the power density, though, nor about the shielding requirements for human habitation. But from my inexpert viewpoint, the energy requirements look like they'd scale.
              • Re:acceleration? (Score:4, Informative)

                by Clith (5063) <rae@tnir.org> on Friday September 14, 2007 @11:00AM (#20603289) Homepage Journal
                Although his math was a bit off, the grandparent's point remains valid.

                At closest approach, Mars is about 56 million km away.Iif we switch the d=½at^2/ equation around, we get t=sqrt(2d/a). 'd' would be ½ the 56 million km distance, to allow for turnover, giving t/2, so..

                t/2 = sqrt( 2 * 28*10^9 / 4.9 )
                t = 59.4 hours =~ 2½ days

                So between 2½ days and a week to get to Mars. Not bad..

            • Re: (Score:3, Insightful)

              by Zaatxe (939368)
              Half a G will get you way further than Mars in a week. The greatest distance between Earth and Mars is 391 million Km.

              You are taking in consideration that the ship wouldn't go from Earth to Mars in a straight line, right?
              Oopsy Daisy!
            • by tehcyder (746570) on Friday September 14, 2007 @11:07AM (#20603355) Journal

              If you don't mind going through the Sun, that 1/2 G will get you Earth to Jupiter, in the worst geometry possible, in seven days and one hour and thirty minutes.
              I'm not a rocket scientist, but isn't that kind of a deal-breaker?
              • by tkw954 (709413) on Friday September 14, 2007 @06:47PM (#20610377)

                If you don't mind going through the Sun, that 1/2 G will get you Earth to Jupiter, in the worst geometry possible, in seven days and one hour and thirty minutes.

                I'm not a rocket scientist, but isn't that kind of a deal-breaker?

                Not if you go at night.

      • Even ignoring the use for robot probes, extended manned missions will still need supply drops.
      • Re: (Score:3, Funny)

        by ozmanjusri (601766)
        Would it be multi G-force worth, that might be impractical for humans.

        Forget humans.

        How much faster will my shark go with this thing bolted to it's head?

        • Re: (Score:3, Funny)

          by Anonymous Coward
          Backwards.
      • Re:acceleration? (Score:5, Interesting)

        by AKAImBatman (238306) <akaimbatman @ g m a i l . c om> on Friday September 14, 2007 @12:50AM (#20599487) Homepage Journal
        As I recall, the computations for reaching Mars in a week were predicated on One-G acceleration. i.e. Earth normal gravity for a ship in transit. To slow down, you simply spin the ship at the halfway point and accelerate in the opposite direction.

        If (and I stress *if*) this invention is not so much hyperbole, it could change the face of space travel forever. We could build interplanetary starships (in this context, ships that never land on a planet) that would be limited only by their power-generation capabilities and not by their reactive fuel. Which means that we could build a ship with a large nuclear powerplant on board, and it could cruise the solar system for as long as its Uranium/Plutonium fuel held out.

        Of course, we still need to solve the problem of high cost of launch, but that little issue would be easier to solve if we actually had somewhere to go once we got in orbit. Scaling up the number of launches would almost certainly bring the price per launch down. In fact, the reason why the Space Shuttle never reached its promised price-per-kilo is because it was predicated on regular launches that never materialized. Starships could change all that. Especially if the cost of moving personnel and equipment was marginalized by carrying more of them per trip.

        For example, I always figured that a special module could be fitted to the Shuttle's cargo bay to carry as many as 60 people to the ISS. Given that the Shuttle has to be man-rated for flight, carrying people makes a lot more sense than hauling around equipment that's better served by a Delta or Atlas rocket.

        How exciting! And probably too good to be true.
      • Re: (Score:3, Informative)

        by Score Whore (32328)
        It seems likely that it would be quite a small amount of thrust, it's photons that you are "pushing" against. Even on the big engine.

        The important thing is that it'll accelerate all the way there. With continuous acceleration it doesn't take much to get going really fast.

        According to the article Mars is 100 Million km away and a big version of this will travel that in a week. We'll assume that you want to stop when you get there so just figure half the trip in half the time (since the second half will be br
        • by E++99 (880734) on Friday September 14, 2007 @02:52AM (#20600125) Homepage
          His demonstration thruster produces 35 micronewtons.

          35 micronewtons / .0005467722 Km/s^2 = 64 milligrams, so if we were using this to power a marscraft with the mass of the acetominophen contained in a single extra strength tylenol tablet, it would be more than 10x too heavy. Of course they said it could be scaled up, but that's a heckuvalot of scaling.

          I doubt the smallesst possible manned Mars vehicle could be less than 1,000kg. That's a scaling factor of 15.6 million. I can jump over 3 feet on the trampoline in my back yard, which translates to a maximum velocity of 4.23 m/s. If I scale that up by 15.6 million, I would be launching myself at 66,000,000 m/s, far exceeding escape velocity, and reaching Mars under my own power in under 30 minutes.
  • by jandrese (485) <kensama@vt.edu> on Friday September 14, 2007 @12:23AM (#20599291) Homepage Journal
    Are we talking about "accidentally cut Venus in half" scaled up? Typically the downside of photonic thrust has been the low power to weight ratio, so for a laser powerful enough to propel a ship to Mars (don't forget that it has to both accelerate and decelerate) that fast I have to wonder just how powerful the laser has to be.
    • by Mothinator (1103295) on Friday September 14, 2007 @12:25AM (#20599301)
      It only says it can get the spacecraft to Mars in a week. It does claim to be able to stop once it gets there.
    • by dethl (626353) on Friday September 14, 2007 @12:28AM (#20599327)
      I would think that scaling wouldn't make the laser bigger but would instead use multiple lasers like they do with ion engines. Of course, IANARS (I am not a rocket scientist) so take what I say with a big grain of NaCl.
    • Re: (Score:3, Interesting)

      by Lloyd_Bryant (73136)

      Are we talking about "accidentally cut Venus in half" scaled up? Typically the downside of photonic thrust has been the low power to weight ratio, so for a laser powerful enough to propel a ship to Mars (don't forget that it has to both accelerate and decelerate) that fast I have to wonder just how powerful the laser has to be.

      If you RTFA, you'll note that the quote about reaching Mars in a week doesn't mention anything about a manned mission.

      The real question: how the hell are they going to power this laser? For micro-thrusts for satellites, solar panels are fine, but for an interplanetary trip you'd need something like a nuclear reactor (unless that "interplanetary vessel" consisted of a mass of solar panels and a payload about the mass of a postage stamp).

      I'd classify this one as just more hype about a technology with an, at

    • by roystgnr (4015) <roystgnr@@@ticam...utexas...edu> on Friday September 14, 2007 @12:50AM (#20599489) Homepage
      To send a ship to Mars in a week, Thrust should be roughly 10m/s^2 times the ship's weight, which we'll say is only ten metric tons. (Because we're getting there in a week, we can pack light... pack light, get it? I slay me.) That gives us 10^5 Newtons of thrust.

      Exhaust Velocity is the speed of light, or about 3*10^8 m/s.

      So our power consumption is 3*10^13 Watts.

      By comparison, the USA is currently consuming less than 1*10^13 Watts on average.

      In other words, if think you think it costs too much to refuel an RV now...

      It's not completely implausible to use light to propel a spacecraft, but either that propulsion will be ridiculously slow (e.g. solar sails, laser sails, or the "precisely tweak your satellite's orbit a tiny bit" applications mentioned in the article), or it's going to require ridiculous "cheap antimatter" amounts of energy.
      • Minor correction (Score:4, Insightful)

        by Harmonious Botch (921977) * on Friday September 14, 2007 @01:17AM (#20599673) Homepage Journal
        To get to Mars in a week, only about 5m/s^2 is necessary. ( Mars at 1G is about 3.5 days, so a week is 1/2 G, turnaround halfway )
        So call it a mere 1.5*10^13 watts.
      • Re: (Score:3, Interesting)

        Thrust is the derivative of momentum with respect to time, and momentum is conserved, so in an open-loop drive F=dp/dt=d/dt(E/c)=(1/c)dE/dt, so power (dE/dt) is force times C.

        But here's where the novel part comes in. Every photon is bounced back and forth thousands of times between the spacecraft and a mirror. The mirror experiences the same force as the spacecraft but in the opposite direction. The spacecraft's momentum comes from "pushing against" the mirror, rather than "pushing against" the exhaust phot
    • by Nefarious Wheel (628136) * on Friday September 14, 2007 @01:55AM (#20599861) Journal
      You could make a laser out of water ice in orbit to any size using fusion purification and rotation of the billet, doping with chromium or rare earths as you go. Thermal mass should keep it solid enough to pipe light through, and if it's long enough you could add energy slowly enough to pump it to some pretty fantastic numbers of photons before the coherent beam left the less-reflective mirror. Fifty metre aperture? Kilometer in length? Mine the ice from the rings of one of the gas giants and use shaped solar reflectors. You could use silicon too, I imagine, but I like ice because it's cool. Plentiful, too, once we evolve past the point of STS and SFS (Space Food Sticks).
    • Re: (Score:3, Interesting)

      by kocsonya (141716)
      > ... I have to wonder just how powerful the laser has to be.

      Well, you can do a back-of-the-envelope calc easily. The mass of the ship is, let's say, about 10 tons or 1E4 kg. You want a 1g acceleration, or about 10 m/s^2 all the way. Assuming a laser with 500nm wavelength a photon leaving will give you an impulse of h/lambda, that is, 6.6E-34 / 5E-7 ~ 1E-27 kg*m/s. Your craft needs to get 1E5 kg*m/s impulse per second to maintain its acceleration, which is then roughly 1E32 photons per second. An 500nm p
  • by Microlith (54737) on Friday September 14, 2007 @12:26AM (#20599315)
    And if scaled up, cockroaches run at 800mph and fleas could jump over a mile. However, the increase in mass and energy requirements would make it impossible.

    Small scale thrusters using only lasers is a good start, but we'll have to see what else gets bigger with scale, other than just the thrust.

  • The Warriors (Score:5, Interesting)

    by PresidentEnder (849024) <wyvernender@gmail.cCOWom minus herbivore> on Friday September 14, 2007 @12:27AM (#20599325) Journal
    At least now we'll have a way to beat the Kzinti [wikipedia.org] when we make first contact.
  • And in response to those two words, I have these eight: "a whole friggin' lot easier said than done".

    <sarcasm>Yup... it's just a matter of scale. </sarcasm>

  • I smell bullshit (Score:5, Interesting)

    by Rix (54095) on Friday September 14, 2007 @12:29AM (#20599335)

    The Bae Institute was founded in 2002 by Dr. Young K. Bae
    In other words, no existing institution would accept the good doctor, so he made his own, and issued a press release written in false third person.
    • Re:I smell bullshit (Score:5, Informative)

      by s4m7 (519684) on Friday September 14, 2007 @01:57AM (#20599865) Homepage

      In other words, no existing institution would accept the good doctor, so he made his own, and issued a press release written in false third person.
      http://www.photonics.com/content/news/2007/September/7/88894.aspx [photonics.com]

      Bae founded the institute to develop space technologies and has pursued concepts such as photon, antimatter and fusion propulsion for more than 20 years at SRI International, Brookhaven National Lab and the Air Force Research Lab. He has a PhD in atomic and nuclear physics from UC Berkeley. Several aerospace organizations have expressed interest in collaborating with the institute to further develop and integrate PLT into civilian, military and commercial space systems, Bae said, and he has recently been invited to present his work by NASA, JPL, DARPA and the Air Force Research Laboratory (AFRL).
    • Re: (Score:3, Informative)

      by Rie Beam (632299)
      His website [baeinstitute.com] doesn't exactly inspire confidence, either

      Bae Institute is a unique institute dedicated to creating revolutionary technologies for the next generation space and medical endeavors, yet aiming at facilitating their rapid implementation and commercialization. For that reason, we specialize in applying highly focused proven technologies to innovative solutions, thereby reducing development time while improving the viability of practical applications. An important goal of the Bae Institute is the c

      • Re: (Score:3, Interesting)

        by Rie Beam (632299)
        Bae also does Acupuncture research [medicalacupuncture.org], if that reflects on him in any way. NASA saw him fit enough to give him a grant [photonics.com], however.

        I don't know what to make of this guy. He doesn't seem like a quack, but I really don't know enough about the subjects to know if what he's spewing is genius or something else entirely.
      • Re: (Score:3, Insightful)

        by dbIII (701233)
        MIT also has a website for a materials science group promoting the idea of ridiculous superhero underwear (ridiculous because being able to spread the energy of impacts is how bullet proof stuff is made so nanometre thick stuff is not going to solve the problem on it's own) that none of their students would believe past first year. Loud Lysenkoism is how things are done these days even if the people actually doing the stuff are legit. We really need work on the K-12 education system because that is all ou
    • Re: (Score:3, Insightful)

      by suv4x4 (956391)
      In other words, no existing institution would accept the good doctor, so he made his own, and issued a press release written in false third person.

      On the other hand even the current institutions started as someone creating them at some point.
      And quite a lot of scientists were ridiculed by the establishment at a time they made a revolutionary discovery.

      What worries me more is his unsubstantiated "if we just scale it up" argument. That doesn't stand basic math/logic/physics.
    • Re: (Score:3, Interesting)

      by Ruie (30480)

      I smell bullshit

      I have my doubts as well. There is a picture there of Dr.Bae standing next to an experimental setup which consists of precision scales, a mirror sitting on these scales, another mirror above it and some sort of laser medium in between.

      From this I figure that his thruster uses Fabry-Perot cavity to amplify amount of light circulating between mirrors - not exactly a new trick. However the press release says something about importance of putting laser medium inside the cavity so, hopefully,

  • by fahrbot-bot (874524) on Friday September 14, 2007 @12:35AM (#20599373)
    Photonic Laser Thruster

    Muuuuch better than using those LASERS without Photons.

    [I hear that adding the photons also makes them lighter...]

  • Energy source? (Score:5, Insightful)

    by StefanJ (88986) on Friday September 14, 2007 @12:44AM (#20599435) Homepage Journal
    Where is the energy coming from to create those photons?

    Since you're dealing with a photon drive, the reaction mass usage (as determined by the classic rocket equation) is going to be negligible for the speeds required for interplanetary travel.

    In fact, I'm not sure what the reaction mass would be in this case.

    But in any case, you're going to need a lot of energy to create that photon thrust. Great phrigging big reactors, which means great, great, phrigging big radiators since you don't have the luxury of a river to carry away your waste heat.

    Antimatter might be a compact way to store the required energy, but converting the gamma rays from matter/antimatter reactions to electricity is going to require heat exchangers and great big radiators as well.

    Well, anyway, scaling this up is going to involve several bears of a problem.

    Also, please note that this "article" is a press release from the guy who made the invention.
    • Re:Energy source? (Score:5, Interesting)

      by Arabani (1127547) on Friday September 14, 2007 @01:06AM (#20599597)
      I did quite a bit of reading on spacecraft propulsion recently (specifically Nuclear pulse propulsion [wikipedia.org] and basically what I got out of it is that if you have a massive energy source (say, antimatter) you're better off just blowing it up and riding the blast wave. You can get extremely high thrust AND specific impulse that way, which is not possible with almost any other engine technology (either high thrust and low specific impulse like chemical rockets, or low thrust and high specific impulse like ion engines). NPP (and its derivatives) is basically the best way we know of right now to get high enough performance for interplanetary, or even interstellar, missions.

      NPP originally started with using nuclear explosions, but more recent research has focused on inertial confinement fusion and even antimatter-catalyzed fusion. The obvious extreme is using antimatter-matter detonations and riding the blast wave, which I'm fairly certain would be more efficient and yield better performance than taking that energy and pumping it into a laser.
    • Re:Energy source? (Score:4, Interesting)

      by zippthorne (748122) on Friday September 14, 2007 @01:17AM (#20599675) Journal
      Since you're using photon pressure, the reaction mass is zero. With sufficient energy, you could travel anywhere in the universe. But unfortunately, Thrust = Power / speed of light.

      Even a 1 Newton thruster requires 300 MW at 100% efficiency.

      You've gotta scale up the power plant to get more thrust, and it's already going to be pretty massive (I believe that puts it on the order of a medium sized commercial nuke plant.) so I just don't see you reaching Mars in a week. Proxima Centauri in a lifetime, perhaps, but no way on the mars thing.

      Of course, since he's talking about a laser, it's possible he means to have the equipment on the ground (or moon, or earth orbit) and propel a much smaller craft. With sufficiently focused optics, you could propel a small probe the whole way to mars (in a week? My envelope just ran out of space...), though it would require some pretty heat-resistant mirrors. Fortunately, the energy requirements for that Newton drop by half when you factor reflection into the equation.
      • Accelerando (Score:3, Interesting)

        by VoidEngineer (633446)
        Of course, since he's talking about a laser, it's possible he means to have the equipment on the ground (or moon, or earth orbit) and propel a much smaller craft. With sufficiently focused optics, you could propel a small probe the whole way to mars (in a week? My envelope just ran out of space...), though it would require some pretty heat-resistant mirrors. Fortunately, the energy requirements for that Newton drop by half when you factor reflection into the equation.

        I highly recommend the book Acceleran [wikipedia.org]
  • "Dr. Bae's PLT demonstration and measurement of photon thrust (is) pretty incredible. I don't think anyone has done this before. It has generated a lot of interest."
    Mead must have meant "incredible" in its proper, older use.
  • I don't want to be skeptical, but...:

    Scaled up, a similar engine could speed a spacecraft to Mars in less than a week.

    Right, just like a scaled up ant could carry a house. In movies.

    But as any junior engineer knows, you can't just scale things up linearly and expect linearly scaled integrity and results.

    In other words, there are solar powered toy cars out there [siliconsolar.com]. But math and physics prevent us from simply "scaling" this up to drive actual cars with linearly scaled up speeds.
  • Meanwhile, it's old-fashioned ion engines for an asteroid mission scheduled for launch later this month, Dawn [nasa.gov], which NASA has now taken to calling "The Prius of Space [nasa.gov]."
  • by suv4x4 (956391) on Friday September 14, 2007 @12:59AM (#20599549)
    I wonder why we don't just scale up a bridge right to Mars and drive to there with a drag racer car. If the latter is too slow, I suppose no problem, we can scale it up as necessary.
  • Incredible! (Score:4, Funny)

    by Riktov (632) on Friday September 14, 2007 @01:38AM (#20599783) Journal

    Senior Aerospace Engineer at AFRL, Dr. Franklin Mead, "Dr. Bae's PLT demonstration and measurement of photon thrust (is) pretty incredible. I don't think anyone has done this before. It has generated a lot of interest."

    Perhaps the demonstration would generate even more interest if it were credible.

  • Scale. (Score:4, Interesting)

    by Rie Beam (632299) on Friday September 14, 2007 @02:00AM (#20599873) Journal
    The problem with all of this is scale, right? The energy required to send larger and larger objects would be impractical.

    So, what's the smallest thing we can send, then? How small can we make a satellite that can send some information back?

    It may not be useful for transporting people to the other end of the universe in a practical amount of time, but I'm sure sending a probe that can check up on Mars every week or so would be of some sort of slight interest to researchers...

    Of course, there's the issue of the touchdown...
  • The BAE Institute (Score:3, Interesting)

    by Rie Beam (632299) on Friday September 14, 2007 @02:24AM (#20600013) Journal
    His institute seems to have a lot of promising ideas, but no real substance. It has three major projects, one of which relies on the photon thruster and some kevlar straps to toss around satellites, and some sort of undeveloped nano-microscrope.

    http://www.baeinstitute.com/ [baeinstitute.com]

    Bullshit, I indeed smell.
  • by Spasmodeus (940657) on Friday September 14, 2007 @02:49AM (#20600117)

    Scaled up, a similar engine could speed a spacecraft to Mars in less than a week.
    Aye. And if my grandmother had wheels, she'd be a wagon.
  • "Scaled up" (Score:4, Insightful)

    by Tim C (15259) on Friday September 14, 2007 @03:00AM (#20600175)
    Because as we all know, it's just that easy! Nothing that worked at one scale ever proved impractical or impossible to do at another!
  • by The Master Control P (655590) <ejkeever@nerdsha c k .com> on Friday September 14, 2007 @03:39AM (#20600335)
    Because until then, you're still paying $10000 per kilogram to low orbit where you can engage the photon drive, which means that no meaningful exploration is gonna happen.

    Did I mention that 45 years ago the USAF tested a nuclear thruster that almost reached 1:1? And how fifty-five years ago they drew up plans for an 8 million ton nuclear-driven starship as part of Project Orion?
  • What's in a name? (Score:3, Insightful)

    by R3d Jack (1107235) on Friday September 14, 2007 @08:40AM (#20601879)
    Isn't "photonic laser" redundant?
  • Buckaroo? (Score:4, Insightful)

    by Mark_in_Brazil (537925) on Friday September 14, 2007 @09:40AM (#20602387)
    Am I the only one getting Buckaroo Banzai vibes from this?

    Dr. Bae of the Bae Institute? Seriously?

    I went to the Bae Institute's site [baeinstitute.com] and found that it is "an independent space and medical research center."

    Physics and space science: check.
    Institute named after its physicist founder: check.
    Medical stuff: check. Dr. Banzai, of course, in addition to being a great physicist, is also a top neurosurgeon. At the Bae Institute site, it says the Institute's medical technologies can be used, among other things, for treating "brain and spinal cord surgeries."

    If Dr. Bae is also the leader of a rock band and says things like "wherever you go, there you are," I'll be surprised if we don't see a wave of stories submitted very soon, all by people named named John, saying that Dr. Bae's research cannot be trusted. I expect these submissions to cite the work of another physicist, Dr. Emilio Lizardo.

    Laffa while you can, Monkey Boy!

    I just showed my age in a way a low Slashdot UID never could.
  • by smithmc (451373) * on Friday September 14, 2007 @02:55PM (#20606667) Journal
    Aren't all lasers "photonic" by definition? Was this thing named by the Redundant Department of Redundancy Department?

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