Slashdot Mirror
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
The material immediately below the leaf is going to be a steel rail, which takes some work to get burning; but this would seem to be a concern if the tracks have some leaves on them; but also leaves/brush/grass/trash/etc. gathered around the tracks themselves. Ablating a thin layer of leaf from a big chunk of steel isn't so bad; but you only have to get unlucky occasionally for bits of burning leaf to fall from the clearance site and land in something suitably tindery and start a decent little fire.
I think the concern isn't dry leaves so much as wet ones that are plastered to the rail like decals on a middle school girl's notebook.
I read the internet for the articles.
"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.
Leaves burn well below the annealing temperature of most steels.
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.