Could someone explain to me how lasers work? (More in-depth than a cereal box explaination!) And what are some examples of what they are used for and how they work. And what are some possible uses and what technical advancements must be met before it’s likely to happen. (For example: How does a cop use a laser to write speeding tickets? How come a laser pointer only shows a red dot when it hits something? WHat’s the range of a laser?)
Try this article first:
http://science.howstuffworks.com/laser.htm
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Laser radars work via the doppler shift of light bounced off of the speeding car (the wavelength of the light gets shortened…knowing what you started with and what you are getting returned to you you can calulate what the speed of the target has to be to make that happen). This is actually how ordinary police radars work as well.
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Laser pointers only show a red dot when it hits for the same reason your flashlight only shows a yellowish.white spot when it strikes a target. You only see light that is reflected back to your eyes. As the laser crosses the room there is nothing for the light to bounce off of and come back to your eye to detect. Once it hits the target does it have something to reflect light. Due to a laser having such tight coherence (not diffuse and spreadout like light from a flashlight) they seem even more ‘invisible’. Technically the lasers is Star Wars/Star Trek/etc. would be invisible till they hit the target but that would make for a boring show (and don’t anyone start with Star Trek uses Phasers, not lasers, and stuff like that).
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The range of a laser is theoretically across the universe. Once the photons are on their way they will keep going forever or till they hit something. Of course, in practice, it will likely hit something eventually. That’s why ground based lasers to shoot down missiles are hard to build. As the laser travels throught the atmosphere it strikes all sorts of stuff floating in the air. As a result the beam is attenuated to the point where it is useless. One way arund that is to make the laser exceedingly powerful so that even if it loses much of its strength on the way to the target there is still enough juice left to do the work required of it. Unfortunately the power requirements are so significant if you want to shoot down a missile as to make the thing impractical to run and hideously expensive (not just the cost of the laser but the cost of a power plant to run the thing).
I also might add that a laser reflector was left on the moon in 1969. That’s approximatley 240,000 miles one way or 480,000 miles for the roundtrip.
That’s not quite right. A laser speed gun measures the time taken for the light to be reflected back. From that, it determines how far away the car is. By comparing successive distance measurements, it can determine speed.
Really? Wow! I wouldn’t think a clock accurate enough to measure the time slices we are talking about here could be made to fit in a handy little gun not to mention affordable. I know very accurate clocks aren’t too much trouble but still…we’re talking about intervals of less (even much less) than 1/100,000th of a second. At that sensitivity even a tiny inaccuracy of the clock would lead to stunningly inacurate speed readings.
Guess I’ll have to go read up on them. They seem much more interesting now.
My high school buddy ground the corner cube reflectors at Lawrence Berkeley Laboratories for that lunar package.
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- The big DIY laser site on the web:
http://www.repairfaq.org/sam/laserfaq.htm
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- The big DIY laser site on the web:
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- Mainly aimed at home experimentors and users, there is at least one type described that gives off a visible beam. YAG or something I thinks…
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No offense Sirreal72, but it sounds an awful lot like you’re trying to write a paper about this subject and you’ve chosen to try to use this board to do your research for you. If this isn’t the case, please accept my humblest appologies. If it is, get out of here and go do some actual research! The rest of the web has lots of resources and it wouldn’t hurt to darken the door of a library or two while you’re at it! Besides, last time I checked, “some guy on the SDMB” is not a valid cite for a research paper. 
Sorry, I’m done ranting now.
Not a problem Marko, you are forgiven…if I hand in a paper on this tomorrow I doubt I’d get a good grade…be like, 7 years late! (Actually, I was a psyc major…so I can’t remember when my last science paper would have been.)
No, I’m just curious…I’ll see an old movie or read a Heinlien book and be amazed how science-fiction becomes science-fact. The problem with the Internet as a resource is that there’s too much info out there, sorting out the chaff is labor intensive sometimes…on the other hand, there’s always someone that knows the answer…or where to FIND the answer. 
How it
works is a good site…but that’s always been my problem with textbooks, they give you the theory without answer the other questions you might have.
What happens if you aimed a ticket laser at another laser? Would it screw up the data or be just as accurate? (Results being doubled b/c it doesn’t have a return trip) Or would the photons interact like opposing streams of water?
What percentage of the laser is able to make the return trip from a source?
Would the stealth bomber’s profile show up, or would it adsorb the laser?
For that matter…does the color of the target matter? Can you measure color by observing something by laser light…does it affect the reflected frequency of a photon? Would it work on a chrome paint job? A mirror?
I understand now how it checks speed (speed of light is constant c, double that is round trip…amount of travel time/2 is distance…comparing samples taken at a measured interval, change of distance equals speed.) This is really amazing, but how hard would it be to to design a three-dimentional scanner?
Position a mirror on a motorized base to swivel back and forth, top to bottom
Aim a laser at it and measure the reflected distance a few thousand times a second…wouldn’t that produce a z-axis? Mount another laser 45 degrees from the “target” and get the x and y? What am I missing here…why hasn’t (or has it?) someone done this? Would resolution be poor?
As far as I know, photons don’t interract with each other.
You mean as a device for measuring the 3-D shape of an object? I don’t think it has enough accuracy for that. But there are 3-D scanners that shoot laser beams at an object and use a camera to measure distance using parallax. (At least I think that’s how they work…) They are used as an input device for CAD systems and computer graphics. Google for “3D laser scanner” and you’ll see plenty of examples.
I knew some guys in college who designed one of these for their senior project. It was really cool. It not only used a laser to measure an object, it also grabbed actual images of the object to use as a texture for the final rendered image.
It was a bit surreal to put a something on a modified turntable inside a dark box, and have a 3D model of said object slowly materialize on a computer.