Lasers: Are they silent? Are they visible?

[Todg]

This question comes up repeatedly on the TML. What are your thoughts. Does a laser rifle make noise when you fire it? Is the beam (or superheated air caused by it) visible?

I recently looked at a video of the THEL laser being developed to shoot down tactical missiles and rockets. Suprisingly, while the laser had enough power destroy an in flight rocket, I didn't notice any beam, or plasma or electrical discharge - all of which are claimed to be side effects of high energy lasers.

Does the beam make a sound? I couldn't tell, because the THEL is a chemical laser and makes lots of other noises.

 

[Jame]

I was wondering this about Traveller lasers, but those are (IIRC) current lasers.

 

[jasper]

I would say no since the current Thel does not.

 

[Andrew Boulton]

Visibility depends on the wavelength of the laser. Visible light gives best performance in an atmosphere, but you can use anything from IR up to UV, or even X-rays, depending on TL. It also depends on the atmosphere - thicker air scatters more light, so makes them more visible. So, in summary: maybe

Assuming a rifle in standard atmosphere during the day, I'd say yes, but not very. Dense atmosphere would increase it, nighttime moreso. Thinner atmospheres and lower power (carbines or pistols) would decrease it.

 

[Andrew Moreton]

The main visibility issue with weapon grade lasers is ionisation of the atmopshere along the beam path creating sparks . The actual photons are going to be pretty invisible unless there is a fair amount of water vapor or dust in the atmosphere.
In exotic atmospheres you may get the trace gases flourescing or similar which would resemble film laser effects.
As to noise the heating of the atmosphere by the beam may well make some sort of nosie as air expands and contracts afterwards , again laser intensity will be the key factor here

 

[mike wightman]

This site may help answer some of your questions Tod

 

[Andrew Boulton]

Nice site!

 

[tucker2]

I always went with the low signature info provided in the MT tables, but that's only 'cause I had no real working knowledge of the things.

How would the general-purpose nature of thr TU lasers affect their signature? They don't seem to be rigged to damage materiel or be antipersonell specifically, and reflec/smoke affect their penetration.

 

[rega_ryan]

I think that it depends on the enviroment they are used in.. We all know that nothing makes noise in space.. No air to carry sound, except inside a ship.. As far as being visible.. Not in space.. Again no air for the beam to react with.. In an atmospere, sound and color, depending on the type being employed.. That`s all I can tell you.. But, I think that is about accurate..

 

[Todg]

Originally posted by Sigg Oddra:
This site may help answer some of your questions Tod

Interesting sight, but I don't think I buy all the conclusions. The comparison of lasers with projectile weapons is tenuous. Also, THEL and MIRACL are megawatt clas lasers, and don't seem produce the ionization that the author posits for kilowatt powered laser weapons.

As for the effects on tissue, I've read a lot of theorizing, but has anyone ever fired a weapons class lasewr into tissue or ballistic gelatin? Does tissue really explode?

I've seen injuries by high voltage/current electricity and those can be messy.

I did find a couple of sites with some hints about laser effect drawn for expoerience with surgical lasers:

http://www.convergentlaser.com/laser_safety.php?slideno=5

Just google for 'laser' and 'tissue'.

Also, I note that heavy duty laser cutters used in industry are typically 1-6 kilowatts. I wonder if anyone has ever tried cutting a steak or other organic matter with one of these.

 

[Linwood]

Don't know about cutting steak with a laser, but I do know of a company that's been successful cutting meat w/ liquid nitrogen!

Here's their website:

http://www.nitrocision.com/

 

[The Hinterworlds Rambler]

Discovery Science had a kickass show on the other night about scientific equivalents of comic book heroes super powers, the show featured that laser that the military is working on to shoot down missiles and planes, it is silent, the beam is invisible, and it is also the sze of two 18 wheeler trucks... good show... they also had a synthetic rope based on spider dragline silk called "Spectra" rope... they had a hlaf inch diameter strand pick up 5 Cars! pretty cool!

 

[Todg]

The laser you saw was the THEL (Tactical High Energy Laser) I was speaking about. Of course, I missed the show. Typical. I though the chemical reaction used to produce the laser made a jet noise.

Spectra is used in bullet resistant vests.

 

[kaladorn]

Todd,

Look at it this way:

If you can deliver enough energy to tissue, which has a high water content, fast enough, you'll sublimate the water. That will be an explosive process.

Now, the obvious question is how much energy would that take? And would the effects be any worse than the injuries from a large caliber projectile?

I imagine the TL-13 laser from MT, which is I believe mentioned somewhere as an X-laser, would likely dig fair sized craters into someone. The shot would usually overpenetrate, but the wound channel would have some fairly nasty burn and fluid sublimation effects.

I know of a couple of electricians who made the mistake of letting some mid-voltage current run through them at something like 400 or 800 amps. One died, the other lost an eye and arm. The one who died had huge whopping chunks blown out of him from the arcing driven by so much energy. Bits of him just blew up/exploded. (This was the result of someone mislabelling a panel and the guys in question not double checking and the system was a power system for some medical systems that required some serious juice).

I'm assuming a laser, supplying heat and energy into the tissues over a very short time, will have effects that are similar.

I further propose that, signature wise, at the TL you can make the weapon, you can generally make a warner for it. By high TL, they'll be small. Maybe built right into people's visors or suits. Now, you say, what point the laser warner? Well, it'd tell you when someone lit you up with a laser sight (you might dodge the follow on shot). The visor might also backtrack the shot, which matters if he didn't hit you and you want to shoot back.

Now, how easy is it to see the shot with the Mark I eyeball? I don't think you will see it, and a small 'crack' would be all I'd expect for sound. Now, modern sound ranging/location stuff could probably pick it out (and future stuff for sure). But that's true of most weapons.

I think the laser would be a low sig weapon, but really wet/misty/foggy days, sandstorms, duststorms, rains, snow, etc. would all serve to give it grief and/or make it more detectable. Also, really cool nights might make picking out heated tracks in the air easier for those with thermal vision systems.

 

[The Hinterworlds Rambler]

Cool! i didnt see if it absorbs shock or anything... does it?

 

[The Hinterworlds Rambler]

And by shock, I mean impacts...

 

[Todg]

Originally posted by kaladorn:
I know of a couple of electricians who made the mistake of letting some mid-voltage current run through them at something like 400 or 800 amps. One died, the other lost an eye and arm. The one who died had huge whopping chunks blown out of him from the arcing driven by so much energy. Bits of him just blew up/exploded. (This was the result of someone mislabelling a panel and the guys in question not double checking and the system was a power system for some medical systems that required some serious juice).

I think the difference here is that current will actually flow through tissue at high enough power densities. That's how you get those deep, nasty woulds. Lasers won't do that. My understanding is that the same energy dump that disrupts tissue will greate an ablative residue which actually blocks further penetration. It appears that lasers, at least the short pulse lasers likely to be used in weapons, won't have the same kind of penetration that KE weapons do. The woun'd are probably less like electrical burns and more like those from a cutting torch.

That doesn't mean that laser weapons wount be effective, but it does mean that deep injury to organs will be less likely. Of course all this is based on the performace of things like medical lasers, which are probably realtively low powered compared to laser weapons.

I further propose that, signature wise, at the TL you can make the weapon, you can generally make a warner for it. By high TL, they'll be small. Maybe built right into people's visors or suits. Now, you say, what point the laser warner? Well, it'd tell you when someone lit you up with a laser sight (you might dodge the follow on shot). The visor might also backtrack the shot, which matters if he didn't hit you and you want to shoot back.

I already assumed that laser detectors will be common. Threat indicators are already in use on aircraft. And laser painters (target illuminators) will be a much bigger worry than laser rifles. Gettting hit by a beam riding missile or bomb will be a Very Bad Thing

Now, how easy is it to see the shot with the Mark I eyeball? I don't think you will see it, and a small 'crack' would be all I'd expect for sound. Now, modern sound ranging/location stuff could probably pick it out (and future stuff for sure). But that's true of most weapons.

I think the laser would be a low sig weapon, but really wet/misty/foggy days, sandstorms, duststorms, rains, snow, etc. would all serve to give it grief and/or make it more detectable. Also, really cool nights might make picking out heated tracks in the air easier for those with thermal vision systems.

OK, this is the crux of the question. It goes back to the whole silent weapon discussion. If a laser is relatively quiet and does't leave an incandescent pointer, and it is relatively lethal, then it makes an ideal snioer weapon: Zero time of flight, no drop or windage. It would be ideal. If it has more of a signature than a conventional weapon, it's out.

As to flash, someone on another list poited out that pulse duration length will be a factor. If the energy pulse of the laser is only a thousandth of a second, it will be less of an issue Than something that lasts a second or more.

 

[The Hinterworlds Rambler]

Imtu, Lasers are the Straightrazors of ranged combat... there are thousands of specific varities, from ones that burn targets to ones that slice them in half... mostly the more deadly varieties are limited to vehicle and automated sentries... many kinds are available, in any wavelength... high Radiation types like x and Gamma Ray versions are particularly deadly, and often expensive or illegal... i always thought that the microwave version is very similar in execution to 40k's "Meltagun" Ouch...

 

[Todg]

Interesting. I've been running Traveller since the later 1970's and in all that time, I've never had a PC carry a laser weapon. Is that weird or what?

 

[Andrew Boulton]

Yeah, they're pretty unpopular in my my games, too. Not sure why.