Ducks in a row

So this passed through my RSS feed from Nature Communications.

Multicolour nonlinearly bound chirped dissipative solitons

Like most of you my brain asked me to please not read that twice. Unlike most of you this falls pretty close to what I get paid to do so I felt obligated to at least try to understand it. Then I says to myself Tim F, says I, this sounds like a varsity challenge in science communication. If internetblog readers can grok why this is new and cool then you sir have made it in the world of unsolicited amateur science writing. You can all grade me at the end to let me know how I did.

Before we get to the meat I’ll toss out this 100% relevant teaser.

Doc Brown

The basic problem has to do with power. Let’s say that you need exactly 1.21 gigawatts of power to go back in time and accidentally seduce your mom. Not saying that you personally want to do this right now, but it happens. The trouble is that even the main line out of a power station will not give you that kind of juice. But that’s ok! You only need it at the exact moment when your DeLorean hits 88 miles per hour. No problem! Use a capacitor.


A capacitor lets you load power in at whatever rate you want and then let it all go at once. A crossbow is another kind of capacitor in that it let go all of your cranking energy in a fraction of a second. In theory you could use nuclear power to fill a capacitor but really you could use a diesel generator, wall current or solar panels if you can afford to wait (and a hefty utility bill).

Now capacitors can store electric power and crossbows work great for hand cranking energy, but sometimes instead of electricity or a hole in Sean Bean you want a whole lot of light. Of course that means lasers. However the kind of laser you find crawling around the average garden puts out a steady steady rate of modest power. If you need a lot of power from a simple laser then you need something like this, a huge power supply and an ocean’s worth of coolant.


On the other hand, maybe you only need that whole lot of laser power when your DeLorean hits 88 miles an hour. You can’t just bottle light up* but you can take advantage of the way lasers bounce light back and forth between two mirrors in an excitable medium (the sapphire in a sapphire laser) until the medium gets ‘hot’ and shoots a laser beam through an aperture. Whereas most of the time light just bounces around a laser cavity like ping pong balls in a lottery, imagine if you could get all those ping pong balls bouncing off each wall one side at a time. A wall would feel mostly nothing and then suddenly A LOT OF PING PONG BALLS and then nothing again. Pulse lasers work like that.


Pulsing is great for communications because they’re essentially digital and because a powerful pulse will travel a lot farther than a continuous wave will. Even better, a focused pulse can put so many photons in such a small space that a decent number will run headlong into other photons and get stuck together into one photon with twice the power (how? quantum something. shut up, it works). To see why this is great for microscope folks, stick a red laser or led against your thumb and see how much of the light passes through. Now find a green laser pointer or LED and do the same thing. Even though the green pointer has more energy none of it gets through your thumb. To see things deep in the brain then, you focus a pulsed red laser on a point deep in the tissue where a bunch of photons will run into each other and turn green at the very very specific spot where you focused the laser. When those green photons hit fluorescent stuff you get yellow light back. As you scan the little focus spot around you get a picture of, e.g., one brain cell deep in its natural environment.

Fascinating. The hell is a soliton?

We all know that lasers are light and light is a wave (yes and a particle; begone pedants). A soliton is a sort of standing wave that happens under certain conditions, like that crest in a river that never goes away. A dissipative soliton is just light bouncing around a laser cavity in a clever way that makes the gain medium (e.g., the sapphire in a sapphire laser) shoot out laser energy in short powerful pulses; think of all the ping pong balls hitting one side of a lottery agitator at the same time.

They figured that out years ago. So what is new?

In theory that should be the end of the story. When you get the standing wave (‘dissipative soliton’) just right the laser head will produce a near perfect train of very short pulses. If you put the laser head on a gimbal to shoot down drones like that Navy bug zapper in the picture above then you are all set. Trouble is you can almost never get away with just pointing the laser head at something. In communications and in microscopes, which is where I use them, you need to guide the laser to the other tin can in Iowa, cells on your microscope or Sean Connery’s scranus by bouncing it down a flexible fiber (yes Goldfinger used a fixed head on a gimbal; bear with me). Frustratingly those perfect little light pulses get a little less perfect every time they bounce around a fiber or any other optical element like a mirror, a filter or a lens.

On the plus side we know most of the things that screw those little pulses up, and a big part of it comes from the ability of lasers to put out an almost but not quite perfect wavelength of color. For example a laser that puts out pure primary green at a wavelength of around 545 nm actually puts out a lot of photons very close to 545 nm plus some with a little more energy and a shorter wavelength and others with less. This inevitable spread becomes really important for pulse lasers, because in a lot of cases a pulse is only useful if it all arrives at the other end at the same time. Bouncing around a fiber makes the longer wavelenghts arrive a little slower and the shorter wavelengths arrive a little sooner than the average photon does, spreading out the pulse and making it a bit less useful.

It gets pretty frustrating to lose your perfect little pulses like that but, critically, each setup causes its own distinct kind of futzy smear. If you can predict the smearing then you can fix it. Think about walking a bunch of kindergarten kids a couple of blocks to a playground. Let’s say that your boss is waiting at the playground so you you really want the kids walking in a tight bunch when they get there, but some kids invariably walk faster than average and some kids invariably take their time. Of course if you want to follow kindergarten best practices you would make the kids hold hands, slow them all down to match the slowest kid or yell at anyone who gets out of step. However you can’t do that with photons so you can’t do that with the kids either.

Not an option.  (credit)

Not an option. (credit)

Now how do you solve it? An optical physicist would set the slowest kids off first, then the average kids and then the speed walkers after some delay. At first your grouping will look terrible but, critically, if you know your kindergarteners and a little math you will impress your boss when they reach the playground in a tight little group.

To pull off this trick with photons, you stick a complicated** little optics box in front of the laser head that lets the low-energy kids out a little sooner and holds back the high-energy kids a little so that they all get to the playground brain, tin can or Sean Connery’s scranus at the exact same time. For lack of a more obvious term to describe this preemptive quantum anti-smearing, we in the lasers world call it pre-chirping. The Russians, Austrians and Germans who wrote this paper made an impact by tackling an especially tough kind of smearing (stimulated Raman scattering) that creates a new solition or standing wave that interferes with the laser pulses. As you might guess by now they figured out how to pre-apply an anti-standing wave that also works in several colors at the same time, a kind of magic trick that only third-level quantum ninjas can pull off.

So to summarize, they needed to separate a bad standing wave from a good standing wave. To do that they pre-anti-futzed each laser pulse with the exact opposite of the bad wave so that kindergarteners all get to their playground in a nice little pack. And it works in several colors! This will probably help high speed traders shave a couple nanoseconds off of their front-loaded trades, and then later it could lead to faster internet speeds and a cooler microscope for me.

(*) OK these badasses basically can stop light in a bottle. Never tell a scientist she can’t do something.
(**) i.e., I don’t know how it works.

56 replies
  1. 1
    shelley says:

    Totally Off topic: This seems to be a weekend of hearing and reading about ducks everywhere. Including a repeat of Prairie Home Companion talking about the march of the Peabody Hotel ducks. Talk bout ducks in a row.

  2. 2
    Baud says:

    tl;dr magic.

    ETA: Fucking multicolour nonlinearly bound chirped dissipative solitons, how do they work?

  3. 3
    Chris says:

    Off topic: God, I love Christopher Lloyd. The kind of actor I’ll watch movies just for the delight of seeing him in.

  4. 4
    Eric U. says:

    tldr; I had Ramen for lunch, is it something like that?

  5. 5
    justwow123 says:

    What’s this?!

    A post where it’s not Cole talking about what a train wreck he is?! How refreshing.

  6. 6
    scav says:

    ever so long, total read, loving the wiggly brain smash.

  7. 7
    safeshark says:

    What’s this?!

    A post where it’s not Cole talking about what a train wreck he is?! How refreshing.

  8. 8
    Citizen_X says:

    (yes Goldfinger used a fixed head on a gimbal; bear with me)

    Sorry, Tim, it has to be done:

    “Do you expect me to read this?”
    “No, Mr. or Ms. Balloon Juice, I expect you to die. Of boredom.”

    Kidding! Seriously, interesting stuff. So when do we get blasters?

  9. 9
    different-church-lady says:

    tl;ra. (Too long, read anyway)

  10. 10
    Ahasuerus says:

    Cool! Thanks for the explication. Question: why does the deep tissue red laser pulse turn green at the focus point? Does the “photons running into each other” act as a frequency doubler or an amplitude doubler? Or is it due to some other effect?

  11. 11
    WereBear says:

    Will these work on genetically modified sea bass?

  12. 12
    Gravenstone says:

    @WereBear: No, I think they have to be actual sharks.

  13. 13
    Violet says:

    So to summarize, they needed to separate a bad standing wave from a good standing wave. To do that they pre-anti-futzed each laser pulse with the exact opposite of the bad wave so that kindergarteners all get to their playground in a nice little pack. And it works in several colors!

    Racism solved!

  14. 14
    Tim F. says:

    @Ahasuerus: It doubles the frequency. Please don’t ask me how. Quantum something. It works.

  15. 15
    Villago Delenda Est says:

    OK, now we need to have Georgi LaForge or B’ellanna Torres explain this in Trek Technobabble,

    So it’s at least comprehensible.

    No, seriously, great post, Tim. Really enjoyed it!

  16. 16
    Villago Delenda Est says:


    So when do we get blasters?

    So uncivilized.

  17. 17
    trollhattan says:

    Brain now officially hurts. Years ago, I had a minor (very minor) role working on NIF when my employer had the beampath installation contract. Can’t adequately describe how huge it is. Have no idea whether their ducks are being released in an organized fashion, but can attest that the capacitors are ginormous.

    Must now make that most difficult of burrito decision: carnitas or abado?

  18. 18
    scav says:

    @Violet: I thought the multi-colored bit was a sneaky part of the advancing wave of gay agendadom. Can we share?

  19. 19
    RobertDSC-iPhone 4 says:

    The only previous instance I’ve heard the word soliton is in the Metal Gear Solid series. The Soliton Radar provided the player with a visual layout of their surroundings and helped the player know where enemies were.

  20. 20
    Villago Delenda Est says:

    @scav: Step. Away. From. The. Rick. Warren. Broadcast.

    Slowly, so as to not alarm the cat.

  21. 21
    Ahasuerus says:

    @Tim F.: Danke. I’ve tried to learn how frequency doubling works, but I’ve never found an explanation that didn’t involve mathematics beyond my pitifully limited intellect.

  22. 22
    scav says:

    @Villago Delenda Est: Hell yes now that it’s a Saber Tooth Tiger, especially one fed on ducklings and errant kindergarteners.

  23. 23
    Derelict says:

    Excellent write-up, Dr. Tim!

    The implications for this also extend to another field that I’m currently involved with that uses pulsed lasers. Lack of range has been a very serious problem for us, limiting our test runs to just a few hundred meters. This technology could be the answer to getting us out to a kilometer or beyond (provided we can get a better handle on atmospheric dust, lensing, and bloom).

    Thanks! And may the soliton be with you!

  24. 24
    🚸 Martin says:

    @Tim F.: Photons don’t directly interact except a much higher energies where they can spontaneously annihilate and form electron/positron pairs. Photons are chargeless, so they otherwise only interact with charged particles.

    When you see higher energies, it’s because they’ve interacted with an atom getting absorbed, thereby raised the energy state of its electrons and then instead of releasing a photon of the same energy, because the pair got absorbed it releases a photon with double the energy (frequency). Requires photons of the right energy interacting with atoms capable of absorbing those energies.

  25. 25
    Ultraviolet Thunder says:

    I work on IR and green pulsed lasers for a living. nanosecond at the moment but I’m moving up to Femto. Our 850 watt average power IR laser will put 2.75MW into a 20ns pulse. And that’s the little one.

  26. 26
    Dave C says:

    More like this, please!

  27. 27
    Violet says:

    @scav: Sure! It’s all part of the liberal soshulist agenda.

  28. 28
    Tim F. says:

    @Ultraviolet Thunder: Sweet. Remember not to look in the laser with your remaining good eye.

  29. 29
    Ultraviolet Thunder says:

    Also: The Pockels Cell that switches out the pulses is a right bastard and the nonlinear crystal that generates the 545nm green from the IR is the King Bastard of all.

  30. 30
    SiubhanDuinne says:

    multicolour nonlinearly bound chirped dissipative solitons

    This is going to be a rotating tag, right?

  31. 31
    Ultraviolet Thunder says:

    @Tim F.:

    Sweet. Remember not to look in the laser with your remaining good eye.

    And run the HEPA filter booth whenever the cabinet is open. And wear the bunny suit. If you sneeze, start over. It’s a headache.

  32. 32
    Ultraviolet Thunder says:


    My new thing, on news stands now.

  33. 33
    Ernest Pikeman says:

    “scranus”? I’m afraid to google it. Scrawny ass?

  34. 34
    ASV says:

    That is some kind of terrible title. Next time budget a verb into your grant, or at least a conjunction.

  35. 35
    SiubhanDuinne says:


    I did, thanks, but not until the wee hours. Let me give it a day or two to figure out if that might work better (or as well) — I’m sure you and Valdivia would like to meet each other, and doesn’t Steeplejack live somewhere in the area?

    I’ll let you know by email.

  36. 36
    Ultraviolet Thunder says:

    IIRC, in fiber communications ‘spreading’ of the pulse is caused by the mixed wavelengths in the pulse traveling at different speeds due to the fiber medium having a different speed of light for each wavelength. This causes a pulse to slouch and spread as the faster wavelengths ended out in front and the slower ones behind. They remediated this by ‘pumping’ the pulse with a signal twice the frequency of the pulse to build the energy back up. Much the way you ‘pump’ a playground swing at twice the oscillation frequency to increase amplitude (height).

  37. 37
    🚸 Martin says:

    @ASV: Verbs are where tenure gets denied.

  38. 38
    Original Lee says:

    This is awesome! I think your explanation was very good. I like the kindergartener analogy quite a lot. Now I feel all smart.

  39. 39
    Ultraviolet Thunder says:


    That’s the whole build, including the PCB. It’s difficult. Nonlinear feedback IC gain amp. It’s tweezer work, and a real headache.
    Personally I use an off the shelf ART Audio Phono Plus USB/analog/phono preamp. It’s a dream.

    I like Audacity software, and the manual is online.

  40. 40
    Ruckus says:

    @Ultraviolet Thunder:
    Got a turntable(audio-tech. at your suggestion!) with a USB output and Audacity software but have been having nothing but trouble getting anything that sounds good out of the software. It’s either flat as a pool table or lots of feedback. I must be doing something wrong. Or maybe not.
    ETA The turntable is great, it’s the software. I can play the records just fine. I get a little frustrated and give up easy on this so it’s probably me.

  41. 41
    Ultraviolet Thunder says:


    Feedback is sound from the speakers getting to the turntable. Isolate them from each other to remedy that.
    Keep an eye on audio level in Audacity and avoid clipping as much as possible.

  42. 42
    gene108 says:


    Off topic: God, I love Christopher Lloyd. The kind of actor I’ll watch movies just for the delight of seeing him in.

    Did you catch Christopher Lloyd, yesterday night, in the SyFy Original Movie Zodiac: Signs of the Apocalpyse?

    IMDB Link

    Did not have the same pacing that made Stonehenge Apocalypse work so well, but Lloyd pulled his weight in this film. The acting overall was solid, but the pace just was did not work as well as other SyFy world destroying movies, in my opinion.

  43. 43
    Jereny says:

    “Multicolour nonlinearly bound chirped dissipative solitons”

    Isn’t that the new Radiohead record?

  44. 44
    gene108 says:

    @Eric U.:

    tldr; I had Ramen for lunch, is it something like that?

    More like this Raman

  45. 45
    low-tech cyclist says:

    @shelley: Maybe they’re making duck soup.

  46. 46
    KS in MA says:

    Thanks, Tim F. If my high school science teachers had explained anything that clearly, I might have stuck with it.

  47. 47
    trollhattan says:

    My favorite De Niro movie.

  48. 48
    EriktheRed says:

    I did read and I think I got maybe 40% of that.

    (I’m being generous, btw)

  49. 49
    dmsilev says:

    Oooh, shiny. I’m not much of an optics guy (all we have is a simple 532 fluorescence setup, which my optics colleagues refer to as ‘that cute little toy’), but that’s a really nice piece of work.

  50. 50
    Joseph Nobles says:

    So this is like a lens for lasers, except it corrects at the source rather than at the target like glasses for the eye. Cool.

  51. 51
    nb says:

    tl;dr scientists are using crossbows to shoot multi-colored ping pong balls at kindergarteners while surfing.

  52. 52
    oldswede says:

    I started to read this post and wandered off to read about Christopher Lloyd instead. Did you know he grew up in the very tony town of New Canaan, Connecticut and that his maternal grandfather was one of the founders of Texaco Oil?

  53. 53
    MaximusNYC says:

    Thanks, Tim! I learned a new scientific term today: Scranus.

    (Perhaps better known as the taint: ‘T’ain’t quite this, and ‘t’ain’t quite that.)

  54. 54
    Aardvark Cheeselog says:

    @Baud: this should be a rotating tag.

  55. 55
    lethargytartare says:


    So? With all due respect to one of our favorite commenters, I think quantum physics is a great practical joke with which only graduate physicists are initiated.
    Kind of like the Masons.

    or lit majors and Finnegan’s Wake

  56. 56
    DaddyJ says:

    I give you an A, Tim. Good use of real-world metaphors. I’d have given you an A+ if you hadn’t played the incomprehensible “Sean Connery’s scranus” before the clarifying mention of Goldfinger.

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