How far can a keychain laser pointer reach ?

Question

Can you also explain what a laser is and why it is able to shine at a very long distance?

Answer 1

Usually miles and miles.

If the question is meant to be how far the light of a laser pointer can propagate, the answer is of course that there is no limit, as long as the light is not absorbed or scattered away in the atmosphere. Of course, much of that light can get from earth to the moon without problems. However, the beam area will eventually become larger due to the beam divergence, so that the intensity e.g. on a screen will be reduced even if the overall power stays constant. Accordingly, an airplane pilot looking down into such a beam from an altitude of 10 km might not be entirely impressed with the intensity.

One may also understand the range of a laser pointer as the maximum distance over which one can send the beam to some screen while still seeing the illuminated spot from the distance. That kind of range is normally not limited by the beam divergence but by the overall optical power (apart from the wavelength and level of ambient light), since the issue is not the comparatively minor divergence on the way from the laser pointer to the screen, but rather the huge divergence of the scattered light on the way back. Therefore, someone standing next to the illuminated screen would easily see the spot when it is already hardly perceivable from the position of the laser pointer.

Answer 2

Keychain Laser Pointer

Answer 3

The rays which emanates from a laser form a perfect monochromatic beam of ligth (only one wavelength = one color). Even if you don't have a lot of power in your laser pointer (see the source below), the lbeam will keep enough power to be seen at a very long distance because the beam is slightly divergent (1mRad for a red He-Ne) = almost collimated = almost parrallel. Then, contrary to our usual lamps, the power is not dispersed in a cone (you feel the power through the heat on your hand near a globe whereas you don't feel anything one meter away, because the energy is shared on a greater surface=lesspower).

So, the laser can reach a point at infinity if there is no absorption. But it is impossible on the earth and useless (I am not for the war:). The absorption of the ligth depends of the wavelength: this property could be very useful ( in laser eye-surgery, it's good to know that the used lasers can't go into your eyes:) because it is stopped by the cornea)

Then, the distance depends of the wavelength, the divergence of the beam, where it is used (air, water...) and what is for you the minimum of required power to say it's shining!

I hope that you have understood me (I am not bilingual) and that I have "enlighten" you:) about the lasers.

Answer 4

Long Distance Laser Pointer

Answer 5

Any old laser pointer could have some of it's photons reach the moon, but nothing significant; most of the photons are scattered through the atmosphere. So you could shine a 1 mW laser at the moon, but you wouldn't SEE it up there. A more powerful laser (I couldn't really tell you how powerful it has to be) could definitely shine and be visible on the moons surface. NASA has actually done this before, aiming it at reflective arrays on the moons surface that were placed in the first moon landing. Whenever anyone says that the moon landing was a hoax, I always tell them this. EDIT: As evocative said, any form of light (electromagnetic radiation) could reach the moon from any source on earth. A flashlight, handheld laser etc would be able to reach the moon. It just wouldn't be visible. If it was large enough to see it on the moon in the first place, we would see a dimmer 'cloud' around the most concentrated point of light. This is caused by the aforementioned scattering of light. (Second edit: I consulted a friend in the field, he said that the spread of the laser, the dim cloud I mentioned, would be many miles wide. Whether or not it's actually visible depends on how much light actually made it) This is caused by the aforementioned scattering of light. Your friend is pulling your leg though, we don't have lasers big enough or telescopes powerful enough to see it on the moon.

Answer 6

It took me a while to line up the direction, but, I eventually pointed my laser pointer due West and it showed on the back of my head from the East.
OK, OK, maybe it was someone else's laser on the back of my head, but, it only showed up when I turned mine on.

Answer 7

Well, it'll make Darth Vader and Jabba The Hutt ( sp? ) think twice about messing with you. LOL! That's two questions! Here, scope this out m'lady:

www.howstuffworks.com

Answer 8

the laser can be seen from miles away but you wont necissarily be able to see it

Answer 9

It's possible to project a spot on the moon's surface with on of them.

Answer 10

I had a simple one that reached a mile.