[alancalverd (OP)]

The object of laser weapons is to deliver a huge amount of energy in a short pulse, to cause failure by adiabatic heating of the target. Most work has been done with carbon dioxide lasers because they are easy to make up to very large sizes, and considerably more efficient than most other solid or gas lasers. Nobody seems to have told the military that atmospheric carbon dioxide has a strong enough infrared absorption to destroy the earth's climate, and they just go on merrily shooting down drone targets, oblivious to the facts of global warming enthusiasts, which clearly prove that they can't work.

[Bored chemist]

The object of laser weapons is to deliver a huge amount of energy in a short pulse, to cause failure by adiabatic heating of the target. Most work has been done with carbon dioxide lasers because they are easy to make up to very large sizes, and considerably more efficient than most other solid or gas lasers. Nobody seems to have told the military that atmospheric carbon dioxide has a strong enough infrared absorption to destroy the earth's climate, and they just go on merrily shooting down drone targets, oblivious to the facts of global warming enthusiasts, which clearly prove that they can't work.

Thank you for clarifying your lack of understanding.
When a molecule in a CO2 laser emits radiation it falls to a lower excited state- rather than the ground state.
It's more efficient to get lasers to do this.
The ground state usually has a very high population- so getting a population inversion is very difficult if the lower state is the ground.

Because the lower state in the CO2 laser is already an excited state, the reverse process- absorption of the laser radiation by the atmosphere- would only happen if the air contained a significant amount of that excited state.
It doesn't.

It's funny how often global warming deniers fail to get the physics right.

If you want to lose this argument in more detail, start another thread.

[chiralSPO]

Bored is quite correct. CO₂ absorbs infrared with wavelengths of about 2.7 µm, 4.3 µm, and 15 µm, while CO₂ lasers emit at 9.4 and 10.6 µm. The absorption and emission windows are sufficiently narrow that the atmosphere is quite transparent to CO₂ lasers.

More research and less snark would make for sounder arguments.

[Petrochemicals]

The object of laser weapons is to deliver a huge amount of energy in a short pulse, to cause failure by adiabatic heating of the target. Most work has been done with carbon dioxide lasers because they are easy to make up to very large sizes, and considerably more efficient than most other solid or gas lasers. Nobody seems to have told the military that atmospheric carbon dioxide has a strong enough infrared absorption to destroy the earth's climate, and they just go on merrily shooting down drone targets, oblivious to the facts of global warming enthusiasts, which clearly prove that they can't work.

I do not doubt that they will create a working laser powerful enough to deliver a milisecond pulse at 10km to burn through armour plating on aircraft, i do not know how feasable it will as it will require a huge ammount in size of hardwear, the power involved and just the sheer technicalities of it.

If you compare lasers to rail guns, where itwill be feasable to create a rapid fire tungsten projectile gun at 5km per hour barrel speed in a fairly small space the laser is along way behind.

Like you say co2 is a barrier and infra red is the least penetrating, you would have thought utra violet would have been a better choice providing less ozone. The current laser can blow up a grenade with a 2 second pulse on a stationary target, or it can set fire to an inflammable drone over a longer period, but really a standard weapons systen could ultimatley destroy this very expensive and large weapon before it was even capable of inflicing damage. It just seems a bit of a white elephant.

[Bored chemist]

Like you say co2 is a barrier

Not really- it's just that Alan was trying to make some sort of point. The air is transparent to some wavelengths of IR, but not others.
The real problem with lasers is pointing them in the right direction, for long enough, and in spite of distortion by the atmosphere, to do any damage.
The military like them because, in principle, you don't have to carry ammunition- just energy, and you can use diesel for that.

[alancalverd (OP)]

Distance is no object - the essence of a laser beam is that it is essentially parallel or focussable to a very small diameter at any distance.

Worth looking carefully at the CO2 absorption spectrum. The bit the warmists worry about is the earth's equatorial emission region, maximal from 8 to 20 microns, with inconvenient (though admittedly small) peaks at 9.4 and 10.6.

[Bored chemist]

Distance is no object - the essence of a laser beam is that it is essentially parallel or focussable to a very small diameter at any distance.

That's why stars don't twinkle.
But, in the real world, they do. Refraction screws things up before absorption does (unless you pick a dumb wavelength)

(though admittedly small) peaks at 9.4 and 10.6.

If the peaks aer small- even for a pathlength of the whole atmosphere, then they may not trouble the military much.

However, if they are small, they are not saturated, so they are the bits of the spectrum where more CO2 means more warming.
So, thanks for pointing out the validity of global warming by CO2

[Petrochemicals]

Well it is focused as the laser at present consists of 8 industrial lasers that focus to the point they aim at, I wonder if they where using a different type of radiation whether they could be focused behind the armour to bypass that all together.

I cannot believe that the gasses in the atmosphere have no effect, even though line of sigt in most military encounters will be limited by the curvature of the earth and the terrain, thus very short distances and low losses of energy. When these lasers are used in cutting, they are brought very close to the cutting surface, I know they may have other reasons, but it just seems improbable thatthey would risk the equipment with close quaters if they didnt have to.

 

[chiralSPO]

Worth looking carefully at the CO2 absorption spectrum. The bit the warmists worry about is the earth's equatorial emission region, maximal from 8 to 20 microns, with inconvenient (though admittedly small) peaks at 9.4 and 10.6.

The "warmists" are concerned about the very intense absorbance that CO₂ has at 15 microns. And yes, it is definitely worth taking a VERY CLOSE look at the spectrum of CO₂. I offer the experimental spectrum provided in the NIST database: https://webbook.nist.gov/cgi/cbook.cgi?ID=C124389&Type=IR-SPEC&Index=1

I will concede that there is a wiggle in the spectrum at about 10 microns, but it appears that at the temperature and concentration used to obtain this % transmittance spectrum, the 10 micron absorbance was at least 5 orders of magnitude less than the absorbance found for the peak spanning 13.5–16.5 microns.

Really Alan, just admit that when you made your quip, you didn't realize that the wavelength of the CO₂ laser was different from the wavelengths at which ground state CO₂ absorbs, and that although you were certain that this little thought experiment proved that the "warmists" were all wrong, it turns out that you only proved that you don't know what you're talking about in this particular instance (I will note that this little confusion doesn't prove the "warmists" right... even though we are)

[alancalverd (OP)]

Don't assume you know what I think, or even what I don't know. I just like to tweak the noses of the warmists from time to time!

It's worth noting that the sun, moon and planets don't twinkle visibly, because the source subtends a larger angle at the receptor than the amplitude of the short-term variations in atmospheric refraction. The refractive index of air at 10 microns is very close to unity at any point in the atmosphere, and a reasonable laser weapon would have an exit port diameter of about 30 cm, so the beam, if focussed to say 1cm diameter at 50 miles, would not be subject to significant twinkle.

It's interesting to input some numbers at this point. A megawatt CO2 laser can be powered by an off-the-shelf turbine or diesel generator. Assuming a 30:1 beam concentration, we are looking at most of a gigawatt per square centimeter, which will melt most aircraft skins even if it won't instantly ablate tank armour. So on a clear day, it's a hell of a practical weapon

But there's a lot of water in the atmosphere - around 10% in a cloud, and the absorbance of water is around 5 x 10³ /cm at 10μm. Firing horizontally to the 50 mile horizon from the top of Snowdon doesn't leave you with much power at the target.

[chiralSPO]

Don't assume you know what I think, or even what I don't know. I just like to tweak the noses of the warmists from time to time!

Oh, I see. You weren't wrong... you're just trolling?

[Petrochemicals]

Don't assume you know what I think, or even what I don't know. I just like to tweak the noses of the warmists from time to time!

It's worth noting that the sun, moon and planets don't twinkle visibly, because the source subtends a larger angle at the receptor than the amplitude of the short-term variations in atmospheric refraction. The refractive index of air at 10 microns is very close to unity at any point in the atmosphere, and a reasonable laser weapon would have an exit port diameter of about 30 cm, so the beam, if focussed to say 1cm diameter at 50 miles, would not be subject to significant twinkle.

It's interesting to input some numbers at this point. A megawatt CO2 laser can be powered by an off-the-shelf turbine or diesel generator. Assuming a 30:1 beam concentration, we are looking at most of a gigawatt per square centimeter, which will melt most aircraft skins even if it won't instantly ablate tank armour. So on a clear day, it's a hell of a practical weapon

But there's a lot of water in the atmosphere - around 10% in a cloud, and the absorbance of water is around 5 x 10³ /cm at 10μm. Firing horizontally to the 50 mile horizon from the top of Snowdon doesn't leave you with much power at the target.

Laser cut steel employs gas to either oxidise or blow the molten metal out of the firing line, not being an expert I cannot say exactly, but its highly probable that it would have a very negative effect on the tduration time needed. Maybe it would even lead to thermal conduction throughout the metal and stop penetration entirely. When initialy cutting plate metal in the middle, a very slow process is used to put an initial hole through the plate to enable cutting

There is also evidence high intensity infra red can have different reactions in air other than refraction. Electron scattering, a5omic saturation and plasma resistance have come up.

[Bored chemist]

Don't assume you know what I think, or even what I don't know. I just like to tweak the noses of the warmists from time to time!

LOL, as if anyone is going to believe that.

You screwed up and don't have the guts to admit it.

if focussed to say 1cm diameter

So, focussed to about the size of the pupil of the eye, and subject to roughly the same level of distortion.
Was that you being wrong again, or "tweaking noses" again?

Electron scattering, a5omic saturation and plasma resistance have come up.

They probably shouldn't have.

[alancalverd (OP)]

Those of you convinced that it can't work, whether due to thermal conduction, electron scattering, atomic saturation, plasma resistance, lens distortion, or any intervening bullshit, should close their eyes and ears before watching

https://www.youtube.com/watch?v=tyUh_xSjvXQ

which shows how much fun the US  Navy  can have with just a 30 kW laser.

There's a significant difference between 2 cm steel (normal industrial specification for everyday laser cutting) and 2 mm aluminum or composite (aircraft wings)  and of course the object of cutting is to make a precise pattern, so you use fairly low power and gas cooling to minimise edge distortion for cutting, compared with high power for adiabatic destruction.

[Petrochemicals]

Yes alan and 10 limes as powerful lasers are being developed, I imagine by upping the amount of converging lasers,  the only problem is the sheer power needed and size of the hardwear. At the moment its really limited at 2000m it takes multiple seconds against soft targets

The Navy has released video of the LaWS on deployment disabling a ScanEagle UAV, detonating a rocket propelled grenade, and burning out the engine of a rigid hull inflatable boat. Officials said it is working beyond expectations. Compared to hundreds of thousands or millions of dollars for a missile, one laser shot costs only 59 cents.

From https://en.m.wikipedia.org/wiki/Laser_Weapon_System

59 sents is 5kwh ? So enough energy to have your kettle going for 30 minutes, the bigger lasers in development will need enough power per shot to have your kettle going for 5 hours ie 50kw, thats either a huge generator or a huge ammount of capacitors per laser,  thats aside from the sheer size of the apperatus. 300kw is probably not going to be enough either, im thinking far larger (giga watt) for shorter periods.

This is the piercing of steel plate, probably not as hard as titanium armour to pierce though.

Edit: And this is probably with the advantage of gas oxidisation probably in the 4kw range ?

[Bored chemist]

https://www.youtube.com/watch?v=tyUh_xSjvXQ

Thanks for the video of attacks on nearly stationary targets where the trajectory is known in advance. As you have mentioned, they needed good weather.
And, unlike such modern weapons as a decent naval gun, they are short range- limited by the curvature of the Earth if by nothing else.

They will need to do rather better before they replace "throwing lots of explosives at the enemy" as a primary weapon of war.
Like amy things, they will have their place in warfare.

Have you forgotten that you started this thread by claiming that absorption in the air would mean these weapons were impossible? You are now saying they are the best thing since sliced bread.

Your original "point" remains wrong.