Lasers

[Cheif Operations Director]

Quick question

does anyone know what the formula for a laser "fanning out" in atmosphere is.

Just to help clarify if you shine a laser toward the sky it's a cone because of the atmosphere does anyone know the formula?

[kerbiloid]

If you shine a laser in vacuum it's a cone, too, due to diffraction.

Minimal spot diameter ~= 1.22 * wavelength * distance / aperture _{say, a mirror diameter.}

All values - in same units, say, meters.

[K^2]

Also, we have a good place for questions that don't merit their own thread.

[Cheif Operations Director]

7 minutes ago, K^2 said:

Also, we have a good place for questions that don't merit their own thread.

Fair enough

[wumpus]

This thread included way to much data on lasers.  I don't think it covers the atmosphere, but should describe how a laser would disperse over such distance (I thought this was besides the point, so didn't read it carefully even when it was posted).  To find information on how much a laser scatters through atmosphere, look up light scattering into (uncorrected) telescopes.  From (multi-decades old, not to be trusted) memory, the best resolution increase of an uncorrected telescope was roughly the same as a 30cm (diameter) telescope, after that the atmospheric issues negated the power of the telescope to increase resolution (but bigger telescopes were still made at the time to collect faint light).

[K^2]

1 hour ago, wumpus said:

To find information on how much a laser scatters through atmosphere, look up light scattering into (uncorrected) telescopes.

To be fair, a lot of that is from density variations in the upper atmosphere. If you're shining light through atmo at sea level, you can probably do a little better. Still, having that as the worst case scenario and vacuum as best already puts some constraints on the question.

[Gargamel]

@Cheif Operations Director, out of idle curiosity, may I ask why you want this info?  When a forum member asks such questions, the scenarios that pop into my head are usually, well, of the "take over the world" variety. 

[Cheif Operations Director]

2 hours ago, Gargamel said:

@Cheif Operations Director, out of idle curiosity, may I ask why you want this info?  When a forum member asks such questions, the scenarios that pop into my head are usually, well, of the "take over the world" variety. 

Hahaha! 

I want it for my rocket. I can have a laser point toward one spot as it rises the cone gets wider and wider. I know this will probroly never happen but I just feel like doing the math for it out of curiosity

Should be more specific the laser is on the rocket

 

-quietly is a corner

"mwhahaha" 

 

[Nuke]

if you want to measure altitude you wold probably be better of with a pressure sensor which can be used as an altimeter with the right math. you can get a breakout board for a bmp085 for a buck on ebay, then use an an arduino micro to log about a minute of data to the eeprom (or use an esp8266 and transmit real time telemetry over wifi). 

 

there was also the method we used in high school rocket competitions. we would stick a couple observers out a known distance from the pad using a very low tech sight with a tilt meter. the angle and known distance from the pad its just a matter of trig to figure out altitude. of course rockets that dont fly straight dont get a very accurate reading.

Edited August 14, 2018 by Nuke

[Cheif Operations Director]

Like I said I was just curious and was only looking into it as a theoretical concept I'm not saying I'm going to tape a laser pointer on my rocket

[Nuke]

8 hours ago, Cheif Operations Director said:

Like I said I was just curious and was only looking into it as a theoretical concept I'm not saying I'm going to tape a laser pointer on my rocket

wouldnt cause much trouble if you did, it just wont work. the laser spot would be bouncing because of vibration and would be moving as the rocket stablilizes itself. now if you had a stabilized laser diode it might work but thats mass. when you need to get an imu just to keep your laser level you could just integrate your position and not need the laser at all. 

[p1t1o]

On 8/13/2018 at 3:48 AM, Cheif Operations Director said:

Quick question

does anyone know what the formula for a laser "fanning out" in atmosphere is.

Just to help clarify if you shine a laser toward the sky it's a cone because of the atmosphere does anyone know the formula?

If nobody has pointed you towards "project rho" yet, allow me to be the first:

http://www.projectrho.com/public_html/rocket/

Tons of stuff on there, its like a collection of science geared towards people writing hard sci-fi.

Some of the weapons-related stuff is a little outdated and optimistic, but overall its an excellent source, at least as a starting point.

Anyhoo, I believe theres a bunch of stuff about lasers that might interest you, even if you arent specifically interested in them as space weapons.