Communication Lasers

[gchuck]

Given that comm lasers are not 'visible' light, how detectable are they 'in-atmo'? Is there heat bloom? Refraction?

I'm working up a scenario where a Sol-Confed recon team has been dropped on a habitable moon, to recon defenses and gain intel on the population.

Timeline is 1119, and support is limited if not completely non-existent.

 

[kilemall]

Generally speaking I deal with laser detection as being a subset of detecting their EM bandwidth, so a UV detector will pick up a UV laser but an IR detector would not, etc.


Lasers would excite atmosphere as they pass through at some level, so detectable, but presumably relatively low power and very short bursts, easily missed.


I'd say they should be able to get away with bouncing their messages up most of the time, subject to more risk the closer they are to people actively hunting them, bases, ships or other space items in LOS, and my favorite, scientists not looking for them at all but happening to have gear that can detect the EM range. Also, should be riskier with two-way comms as presumably ships or satellites would be 'known' and lasers emitting from them towards the ground would get attention.

 

[mike wightman]

Can you see the beam from a laser pointer - nope, not unless there is something in the air to scatter some of the light such as an aerosol spray or chalk dust.

You are in a similar situation with a comm laser. Can the detector 'see' the beam, nope not unless it is scattered off something.

 

[kilemall]

Can you see the beam from a laser pointer - nope, not unless there is something in the air to scatter some of the light such as an aerosol spray or chalk dust.

You are in a similar situation with a comm laser. Can the detector 'see' the beam, nope not unless it is scattered off something.

He's shooting through atmosphere presumably on a mission, that's what I'm talking about.


Example-
http://news.mit.edu/2016/infrared-laser-detect-atmospheric-chemicals-0628


Presumably a spec ops recon team would be using millisecond burst lasing and would pick a bandwidth optimized to reduce detection, but a military/security site is going to expect that and ramp up detection arrays, most notably in satellites or patrolling craft.


So there should be all sorts of precision timing in getting their data out to avoid detection, something clever about what they are lasing to get the message out that doesn't excite interest, and maybe a remote sending site to avoid spotting on the ground or aerial patrol.


For extra pucker factor, give the team an experimental laser comm that is supposed to be tuned to not be detectable with this specific atmosphere, but which is too easily blocked by said atmosphere and it takes several tries to get messages out/extraction request done.

 

[mike wightman]

Reading the article you have linked to - the laser is scattered off the pollutants etc that they are tuned for.

I agree with you that comm laser would be tuned to ineract with the bare minimum of atmospheric gasses, which means the only way to detect it would be to be the target reciever or to catch some of the reflection from the target receiver.

 

[kilemall]

Reading the article you have linked to - the laser is scattered off the pollutants etc that they are tuned for.

I agree with you that comm laser would be tuned to ineract with the bare minimum of atmospheric gasses, which means the only way to detect it would be to be the target reciever or to catch some of the reflection from the target receiver.

Hmm, gotta have that 'transporters are down captain' pucker factor for the needs of the story/excitement, so another potential factor that could increase detectability/failure is weather.


That and whatever they are bouncing off of has to be pretty darn close to keep the power down and the beam narrow enough to not get picked up inadvertently. That is going to have to be very rare precision movement for something natural in orbit or on approach/departure. Eyes will be on that, so may have to offset or wait until the receiver is masked and not LOS from government/base/patrol/satellite sensors.