Laser beamed power question

noosfractal · 2005-11-02 03:19:16

I understand how an atmosphere causes laser beam dispersal (widening of an initially narrow beam), but what causes beam dispersal in a vacuum? Is it possible to prevent with clever optics?
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C M Edwards · 2005-11-02 09:18:57

I understand how an atmosphere causes laser beam dispersal (widening of an initially narrow beam), but what causes beam dispersal in a vacuum? Is it possible to prevent with clever optics?
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Saddly, no, because one of the main causes of attenuation in air remains in space: spreading of the beam area (dispersal). Clever optics can reduce this dramatically, but the coherence length of the laser (a measure of how "clean" the light entering the optics is to begin with) limits the effectiveness of any optics used. No laser has an infinite coherence length, so even a dramatic reduction in dispersal still can't stop spreading at planet-scale distances.

There will always come a point at which you get better transmission by stepping up the laser's power than by fiddling with its optics.

SpaceNut · 2005-11-02 09:59:29

I recall a mission that would look for gravity waves using lasers, so they must have figured out this problem or this missions is doomed to failure.

Good the link is still active on the story...
LISA and the search for elusive gravity waves

noosfractal · 2005-11-02 14:08:41

From

http://powerweb.grc.nasa.gov/pvsee/publ … _3213.html

r_spot = 0.61 * d * λ / r_lens

So r_spot, the beam radius at the receiver (containing 84% of the initial beam power), is proportional to the distance from the sender to the receiver, multiplied by the wavelength of the light, and divided by the radius of the sender (r_lens). So we need to decrease the wavelength (UV, x-rays, etc) or use very large senders - the same huge scopes that the astronomers use, but in reverse.
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MarsDog · 2005-11-06 22:24:35

Interesting reading on lasers from:
http://amasci.com/miscon/miscon4.html#lase

Laser light can be FORMED INTO parallel light,
while the light from ordinary sources cannot

Just imagine the capabilities of a large orbiting military satellite if an array of
lasers could be phase locked, steered to target a very small object.

SpaceNut · 2006-01-06 11:17:09

This is probably one reason for why the MTO has been cancelled at this point and hopefully it will be revived in time for manned missions to mars.

Longest laser link bridges the gulf of space

A laser communication link has been made across a record 24 million kilometres (15 million miles), between the Messenger spacecraft and instruments on Earth.
The craft and the ground station transmitted pulses back and forth to each other, and although no actual information was transmitted, the experiment shows the potential for interplanetary laser links.

Mars_B4_Moon · 2022-09-22 14:55:35

SpaceX Is Testing Out Starlink Internet in Antartica Using Space Lasers

https://gizmodo.com/spacex-starlink-elo … 1849546505

Mars_B4_Moon · 2023-12-23 08:29:13

NASA Tightbeams a Cat Video From 31 Million Kilometers Away

https://www.universetoday.com/164930/na … ters-away/

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#1 2005-11-02 03:19:16

Re: Laser beamed power question

#2 2005-11-02 09:18:57

Re: Laser beamed power question

#3 2005-11-02 09:59:29

Re: Laser beamed power question

#4 2005-11-02 14:08:41

Re: Laser beamed power question

#5 2005-11-06 22:24:35

Re: Laser beamed power question

#6 2006-01-06 11:17:09

Re: Laser beamed power question

#7 2022-09-22 14:55:35

Re: Laser beamed power question

#8 2023-12-23 08:29:13

Re: Laser beamed power question

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