Built on Facts

Seeing Laser Beams

Ok, see counselor Troi firing her phaser?

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You see this kind of thing all the time on film in scifi. Whether it’s Star Trek, Star Wars, or pretty much anything else, energy beams fired from future weapons are visible. Usually someone will point out that in fact laser beams are not visible in this manner. To see light, it has to reach your eyes. This is clearly not possible when all the light is actually traveling down the beam path. You can see this in action with laser pointers – only the spot where the light hits and diffusely reflects is visible. The path is not.

Writers of TV shows usually explain this by saying that the beam is not strictly light, but some stream of particles that slightly emits to the sides along its main path. While this has its own problems, at least it acknowledges the issue.

But what’s even more interesting is that in fact there are already automatically particles present along the beam path in the atmosphere. Some of them are sizable particles like dust, others are individual atoms and molecules. Generally they don’t scatter much light, but if the light is intense enough then the small amount they do scatter is enough to see. And so you have a visible laser beam. Here’s one in my lab:

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The beam scatters off the air and you can actually see it as a straight line. Apologies for the terrible camera phone picture, I really need to get a classy camera that can take nice pictures. This is not actually a laser I’m working on, so honestly I’m not sure which variant of frequency-doubled Nd:something laser this is. Probably Nd:YLF.

This is used to pump an infrared ultrashort-pulse laser with a repetition rate of 1 kHz. This can itself be focused to a point in the air, which becomes visible as a little stationary spark as the intense beam ionizes the air. This produces a 1 kHz buzz which can easily be heard by the unassisted ear.

I have to say it’s a nice job perk that I can see old science fiction tropes come to life pretty much every day. :)

Comments

  1. #1 Nathan Myers
    November 19, 2009

    Good shot of the Ship’s Channeler breaking character.

    Kids today might not know about channeling. Back when they started ST-TNG, channeling was a big deal. There were lots of best-selling channeled books, so The Future would have to have had channelers too. Channeling meant listening to “spirit guides”, and transcribing whatever they said. I had a friend with a spirit guide named “Jacques” who had been a fur trapper — the spirit guide, not the friend. I never noticed Jacques ever being especially helpful.

    The ship’s channeler on TNG only got to shoot beam weapons after people started grumbling that she never actually did anything. It was pointed out after she did that she had, somehow, succeeded in graduating from Star Fleet, and would have had to have learned how to work one.

  2. #2 John McKay
    November 19, 2009

    The reason you can see the beams is that they only boldly go to places where the air quality is terrible.

    What I find more amusing are the shows where you can see the front end of the beam moving toward its target. This has to mean that, in the future, death rays will be slower than a speeding bullet.

  3. #3 Omega Centauri
    November 19, 2009

    The silly thing is that if those really were high power laser beams, in any sort of frequency subject to reflections, you would want to be wearling safety goggles, long before the intensity become high enough to do bodily harm -let alone instantly kill or vaporize stuff. But one could argue the beam of whatever is strong enough that the visible path is a nonlinear effect, since as all sci-fi fans know, laser beams are just as visible in a vacuum. They also make a noise in a vacuum.

    In anaology to world war two, tracer rounds were added to anti-aircraft weapons, so that you could follow where they were going. So I suppose you might want to do something like that with your phaser.

  4. #4 John McKay
    November 19, 2009

    Troi wasn’t a channeler; she was an empath, an idea which must have sounded cool in the brainstorming sessions for the show concept, but was totally lame in practice.

    Alien: (sitting on dark and cluttered bridge) Captain Picard, I will utterly and completely destroy your race! I’ll burn your homes, salt your fields, drive off your women, and rape your cattle. I’ll grind your bones to make my bread! I’ll use the burned out hulk of your puny ship as a bedpan!!

    Picard: (expectantly) Counseller Troi?

    Troi: (looking constipated, but still hot) Captain, I’m sensing hostility.

  5. #5 Nathan Myers
    November 20, 2009

    I can tell, John, that you never had much contact with channelers. They didn’t just listen to voices in their heads, they would carry on about auras and emanations as long as anyone would listen. It must have been a good time to be schizophrenic.

    Most of the scripts, really, bore a strong resemblance to channeled writing. (Emphasis on “bore”.) Patrick Stewart’s voice was all that carried that show.

  6. #6 Tony P
    November 20, 2009

    Closest I ever got to lasers was repairing a 150W CO2 laser engraver.

    It used an RF exciter to get the tube to lase. That meant it needed a water cooling system. Well one day someone forgot to switch on the cooling unit and POOF, there went the lasing cavity. I did comment to the machine vendor that it was a rather stupid design since they didn’t utilize a coolant interlock before allowing the laser to come to full power. I wasn’t very popular with them for awhile after that.

    And yes it was an infrared laser. So you didn’t ‘see’ it but it could etch metal.

  7. #7 Dunc
    November 20, 2009

    Whether it’s Star Trek, Star Wars, or pretty much anything else, energy beams fired from future weapons are visible.

    And slow enough to dodge.

  8. #8 rob
    November 20, 2009

    in Hilbert space, no one can hear you scream.

  9. #9 Uncle Al
    November 20, 2009

    A two-beam weapon is required. One beam is purely magnetic, the other purely electric. It is only when they intersect that they go EM. No, wait! One beam is time-like, the other space-like. It is only when they intersect… No, wait! One beam turns off positive charges, the other negative charges. There is no need to hit the target. Hit on either side and… crunch! (Do Not Use In Air)

    No, wait! Beware the improvised economic device, the Death TARP. One beam taxes, the other subsidizes. Everything in-between dies of social activism – the Obamatron! (2000 page user manual)

  10. #10 John McKay
    November 20, 2009

    Nathan, what we have here is a splitter/lumper controversy. You’re combining things that I prefer to separate. I don’t think there is any disagreement between us over anything except terminology. Channeling is being a conduit for another being. Reading auras is something else. Healing by manipulating “energy fields” is yet another thing. Troi’s empathic power was supposed to be watered down telepathy, and it was pretty useless for the plots. I’ve had a lot of contact (and still have) with that community. I agree with you most of the people who claim one power also claim others; I just prefer more specific names than calling them all channelers. At least, in my experience, that has been what they prefer. My generic term for the whole New Age enchilada and its historical predecessors is spiritualism.

  11. #11 Yaque
    November 20, 2009

    About the only thing I liked about Star Wars were the weapons, which I decided were various methods of plasma emitters enclosed or something by magnetic fields (or something). NOT lasers!
    So you could see the “rifles” spitting out these small blobs of glowing plasma in bullet sized magnetic (or something) bottles which would contain the plasma long enough to hit something.
    This explained the white ceramic armor nicely. And the shielding for the ships, which would disrupt the magnetic containers and so dissipate the plasma.
    The light-saber would then be a “rod” of glowing compressed plasma that would have to be contained by a far more sophisticated field generated by the handle.
    Difficult and arcane, to be built only by adepts.
    (Of course the user’s hand would be crisped after holding something like that for a minute.)

    This explanation satisfied me enough that I was able to enjoy the first three movies, but no more!

    The only thing that bugged me in the first movie was how they blew up a that planet in an instant.
    It should have taken hours (at least) to pump enough plasma in to do anything noticeable to a whole planet.
    Could have made a good sequence!

  12. #12 Nathan Myers
    November 21, 2009

    They can ask to be called “spiritual engineers” if they like. Around here it’s all just Woo. But “Ship’s Woo” doesn’t have the ironic dignity of “Ship’s Channeler”.

  13. #13 Dave
    November 21, 2009

    OK..so they called it a Phaser,which means it can have any quality’s the writers want.it’s not a laser,energy packet thrower or whatever.it “phases” and on any program did anyone ever say how it worked,i know one of the crew just wrote off how the transporter worked as something the big brains in science understood..ok–how about this..the sound you hear in space is the energy field from whatever powers the craft and it may not be “sound” that your hearing but the waves from the “engine” passing thru your ear’s nerves/brain cells,or something like that.thats why sci-fi is so much fun,you just roll with the punch and move on.

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    I don’t think there is any disagreement between us over anything except terminology. Channeling is being a conduit for another being. Reading auras is something else. Healing by manipulating “energy fields” is yet another thing. Troi’s empathic power was supposed to be watered down telepathy, and it was pretty useless for the plots.

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  18. #18 Dunc
    November 23, 2009

    OK..so they called it a Phaser,which means it can have any quality’s the writers want.it’s not a laser,energy packet thrower or whatever.it “phases” and on any program did anyone ever say how it worked

    The canonical answer is: “They work just fine, thanks.”

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