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Trains May Soon Come Equipped With Debris-Zapping Lasers
Molly McHugh writes: Holland's chief transportation service is testing a unique new way to clear the rails of fallen leaves and other small debris: by mounting lasers on the fronts of locomotives. The lasers will cause the leaves, which produce a condition commonly referred to as "slippery rail" in the fall and winter months, to vanish in a puff of smoke.
Wouldn't it be easier to mount brushes or something?
I would think that it'd take one heck of a laser to fry wet leaves on a train track. The whole thing sounds like a boondoggle to me.
The simple truth is that interstellar distances will not fit into the human imagination
- Douglas Adams
Maybe I'm just a terrible person whose sense of childlike wonder and love of lasers has shriveled; but isn't 'clearing leaves' the sort of job where a simple nozzle blowing compressed air(turned on and off based on sensor input if it turns out that you can implement a sensor system at lower cost than just running the compressor a bit more often) at the track immediately in front of the wheels would be more than adequate for the purpose?
My understanding is that some trains even have a compressed air supply already(for pneumatic braking and sundry other duties), and all trains, since they have to move, are going to have a fairly burly supply of either mechanical or electrical energy to run a compressor. Much simpler and likely more durable than a laser and optics high-powered enough for debris clearing, and less likely to cause amusing track fires.
Am I missing something here, or did somebody just fail to KISS?
Wait.. "puff of smoke" ? If the lasers are powerful enough to do that, what's keeping it from setting things on fire?
"Trains May Soon Come Equipped With Debris-Zapping Lasers"
The lovely word "may" is such an abused word. There are MANY things that MAY come, on the other hand it MIGHT not as well. My money is on that it won't be here anytime soon. There are so many technical and impractical issues that arise, that this is nothing more than a "wow...lasers, we're so 1337" 21 century etc. Sure, it makes for a good read, and even better...the house-geek will have his say over the dinner table...say...did you know honey, they're putting lasers in front of the trains now to clear the tracks. OOOOh honey, that's just up your Dart Vader alley!
Guess what? I've been working with technology and prototyping for years, and it's a riot every time this actually surfaces as an article once in a blue moon, you can't just put high power lasers in front of trains, you'll have reflection issues, IR-radiation, people claiming blindness, and the kind of power you need to "zap" it clean is extreme, this isn't your average laser pointer that can be used to write your name into a cellphone or pop balloons, heck...even hefty industrial lasers used to cut metal are so focused and concentrated that if you wanted to use it to blast away debris...you'd need a HECK of a lot more space for it to be actually practical, not to mention the need for cooling.
What this world is coming to - is for you and me to decide.
It's called the Netherlands. How difficult can it be?
Sig?
Seems like it would take some careful calibration to make a laser that would burn off wet leaves plastered to the rail and yet not soften the hardened steel of the rail that's going to have a multi-ton train passing over it in seconds.
If you RTFA, they use a laser wavelength that reflects off the steel instead of being absorbed.
[Fuck Beta]
o0t!
Leaves burn well below the annealing temperature of most steels.
Note: Due to lasers, it is no longer safe to lye on the rails in front of oncoming trains.
Sorry to reply to myself but since Wikipedia doesn't actually bother to talk about mechanisms, I will. You can remove a surface with a laser through heating, which applies enough photons to the surface atoms that they vibrate loose, which is a slow process that transmits piles of heat downwards. Or you can use a laser whose wavelength is shorter than the strength of the sigma electron bonds in the material, in which case the electrons absorb the photons, get popped into a higher orbital, and the bond that held the two atoms together simply isn't there anymore and the now free atoms can just drift away. There is in theory no heat generated at all. In practice there are so many photons coming in all at once that there's a metric buttload of photons being absorbed by everything, so what actually happens is the wavefront hits and turns the first couple of atomic layers into a plasma, that erupts away from the surface and leaves the underlying surface close to untouched. So that's the mechanistic difference between burning and ablation: photon flux and wavelength.
Nostalgia's not what it used to be.
About a decade ago the Brits had a slew of leaves-on-the tracks failure-to-brake accidents. Why now? everyone thought. In a bunch of places the embankments had been designed for coal-burning trains, which spit sparks, so the embankments were gravelled or very sparsely grassed. What trees the fires didn't suppress were cut down as seedlings every few years.
Time passes, the engines change fuel, someone notices they're spending money on maintaining the gravel and stops.
*Decades* pass and there are beautiful trees on the embankments tall enough to shed onto the tracks -- *that's* when the accidents start.
Ablation can in theory remove single atomic layers with thermal damage only a few atoms deep to the underlying surface.
So the damage to the surface is only a few times larger than what was removed?
The damage is only a few atomic layers deep, more or less independent of how much material is removed.
A large limitation to how much you can remove is that you build this huge largely opaque cloud of debris blasting off the surface of the material so you can't get new photons into the surface anymore, but you can peel stuff off a few atoms in a burst or a few dozens of micrometers in a burst, with the same very thin heat affected zone at the surface. (Another is that all the stuff you just blasted off immediately sticks to the front of your objective lens, but they don't last long anyway when you have this many photons going through them: objective mirrors last longer but still get covered in junk. Some interesting stuff being done using liquid waveguides through which the laser moves and which wash off the debris, but then you have to not vaporize/ablate your liquid waveguide. And at least with the UV stuff we were doing, even the atmosphere absorbed giant amounts of the energy, so we had to do it in a vacuum and that made the crap-sticking-to-the-lens problem even worse.) My recollection is that people were trying to use laser ablation to do extremely thin heat-treatment, like surfacing treatment, but couldn't actually get it thick enough to make a measurable difference in wear characteristics, but A: I may misremember and B: people may be better at this now, so that bit could be complete hooey. I got out of high-energy lasers like fifteen years ago, when I realized that fully half my coworkers had pie blindness: they'd managed to damage some part of their eyes so they were missing some of their visual area, and stuff may have progressed a lot since then.
Nostalgia's not what it used to be.