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Post by michalo on Dec 26, 2016 19:35:11 GMT
I made a 10 GW, 265nm UV laser with 341MW output, and 2.02 PW/m^2 intesity at 10km. I thought: Hey, that's gonna cut through enemy ships like Death Star! Well... nope. At 10km, it still takes more than a second to cut through 10 cm of silica aerogel, and this laser has power which can melt a TON of silica aerogel in 1.9s if the light would be fully absorbed. It looks like that something around 99.9% of the light is reflected by aerogel which is visually quite black, and the rest is somehow dissipated inside of aerogel, which has absurdly low thermal conductivity, so it avoids being turned into plasma. This laser unleashes 341 MW at area of 0.16mm^2, and this energy has to go somewhere. Could somebody explain this phenomenon, because I feel like my explanation isn't quite sufficient or possible  Is this a bug or physics works that way? |
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Post by teeth on Dec 26, 2016 20:07:08 GMT
That's probably because your aperture is so large, the beam is so tight that your targetting system can't keep it in the exact same spot all the time, so instead of burning through you're making a 0.16mm wide trench as the beam moves around. Try reducing the aperture size to damage a larger area, or increase the range to 1000 km and see how it works.
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Post by amimai on Dec 26, 2016 20:16:59 GMT
its why I designed the rainbow machine!
6 different laser wavelengths from 6 separate lasers makes a nice range of spot diameters
low wavelengths burn meter wide beams into the target while the smallest wavelengths generate tiny beams that punch holes through anything, combined it makes for a multi-purpose weapon system capable of taking on any target at any range
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Post by michalo on Dec 26, 2016 21:13:06 GMT
I don't think that 'time of exposure' really matters here: (All this calculations are based on middle school / early highschool thermodynamics and can be utterly false, they assume the energy transfer is 100% efficient etc.) area = power/intensity = 341 000 000 / 2 020 000 000 000 000 = 1.68 e-7 m^2 volume = area*height = 1.68 e-7 * 0.1 = 1.68 e-8 m^3 mass = volume * density = 1.68 e-8 *100 = 1.68 e-6 kg deltaE from absolute zero to 773K = mass*specific heat * deltaT = 1.68 e-6 * 840 * 773 = 109 J time = E/P = 109/341 000 000 = 3.19 e -7 seconds = 319 ns I don't think the beam movement can influence really much here  Edit: I had written 202 PW instead of 2.02 PW (which is the intensity at 1km instead of 10km). Corrected now. |
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Post by amimai on Dec 27, 2016 0:59:54 GMT
a wizard did it!
actually the way some low density materials manage to survive inordinate amounts of laser damage is a tad weird when you think about it.
a 100MW(output) laser would be melting 150kg of silica gel(1500cc), even assuming the laser has 1% absorption efficiency that's still 15cc of silica gel every second
vs large waist lasers(10cm+ spot diameter) silica aerogel should simply liquefy after a second or two because the energy it has absorbed is simply too much for it to contain regardless of thermal diffusion, radiation, or ablation effects
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Post by apophys on Dec 27, 2016 1:44:20 GMT
When you melt/boil a spot of armor, further heating will heat up the already-destroyed material, which needs time to clear out of the hole. In result, there's a cap for damage propagation speed. I.e. use a bigger spot size - shrink your aperture. You'll damage a larger area at the same rate as you do now for the smaller area (will help counteract targeting inaccuracy).
There's a spreadsheet for critical laser intensities for a few materials on the standards thread. In short, aim for ~ 1-5 MW / m2 at max range.
Continuous lasers (like we have) suffer from this more than pulsed lasers. We need Q switches!
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Post by lieste on Dec 27, 2016 1:57:39 GMT
Yup, just boiling the material isn't enough. The vapour remains at the target site and is heated by over powered lasers, essentially protecting the unvapourised material for longer than it would at lower power density.
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Post by amimai on Dec 27, 2016 2:21:00 GMT
Yup, just boiling the material isn't enough. The vapour remains at the target site and is heated by over powered lasers, essentially protecting the unvapourised material for longer than it would at lower power density. lol no... 1. vacuum acts as the best gas dispersion system in the universe, the instant you make some hot gas, it goes shooting away from impact point as fast as it can 2. molten and gas state armour INCREASE laser absorption rate 3. lasers can transmit through gas state material and end up heating an even larger area, resulting in even MORE damage because small waist beams will generate large spots increasing the local temperature, while reducing local heat diffusion rate think of it this way(bit extreme, but the energies you are dealing with are in the MW range... some of my nukes generate less energy) A)a 1mm waist beam hits a piece of armour A1)boils away 1mm of said armour creating a small cloud (most of energy is reflected) A2)heats local area to +100k (which in terms of SiGel reduces its laser resistance by at least 1/7th) B)laser continues to hit same spot (roughly) B1)gas cloud diffuses beam, beam heats local area +200k B2)beam burns armour, +50k local area (armour temperature +350k in an area of ~10cm) C)laser continues to hit same spot (roughly) C1)gas cloud diffuses beam, beam heats local area +200k C2)beam burns armour, +50k local area (armour temperature +600k in an area of ~15cm) D)laser continues to hit same spot (roughly) D1)gas cloud diffuses beam, beam heats local area +200k D2)beam burns armour, +50k local area (armour temperature +850k in an area of ~20cm) D3)local armour melts D4)beam transmission occurs through 20cm of SiGel D5)1mm*20cm of SiGel explosively vaporise along beam vector (resulting in 100g of vapour with 100MW of energy, basically a nuke going off in your armour) D6)vaporised SiGel violently explodes, you now have a nice 50cm hole in your armour... |
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Post by lawson on Dec 27, 2016 2:49:43 GMT
When you melt/boil a spot of armor, further heating will heat up the already-destroyed material, which needs time to clear out of the hole. In result, there's a cap for damage propagation speed. I.e. use a bigger spot size - shrink your aperture. You'll damage a larger area at the same rate as you do now for the smaller area (will help counteract targeting inaccuracy). There's a spreadsheet for critical laser intensities for a few materials on the standards thread. In short, aim for ~ 1-5 MW / m 2 at max range. Continuous lasers (like we have) suffer from this more than pulsed lasers. We need Q switches! This limitation is purely in the physics simulation of the game. Common industrial laser cutting processes run near 1Tw/m^2 and they still get cutting speed gains from more power. (and cutting feed rates are commonly 10-100 inches/minute or more) "But assist gas!" The assist gas does help cutting rate some. My most recent search showed that it allows for faster cuts to be made by just melting the target instead of vaporizing it. But with 10-400MW on tap instead of a mere 1-10Kw of current industrial lasers I don't think assist gas would add anything to the super-sonic outflow of armor plasma caused by the laser. Armor's that create a lot of soot when they vaporize most likely would slow down the cutting laser. But if the soot absorbs most of the laser you end up with up to a ~300MW laser powered plasma light bulb located millimeters from the armor surface. So your armor survives longer because a larger area is ablating, but it's a loosing battle. |
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Post by michalo on Dec 27, 2016 10:18:54 GMT
I just figured out that something is very wrong with laser damage system - it looks like it always waits until the first hit object is destroyed, before damaging the second. You can armor ship with fused quartz against lasers and it is going to work fine, ignoring it's 96% trasmittivity against 265 nm light and you are trying to hide behind a ultra-fine glass window. Similar thing happens to aerogel, which is in fact very porous glass - it has 100% transmittivity, and since only extremely small fraction (I don't know if my calculation is correct, but it looks like it is 1.45e-9 of beam power) of the laser light is actually absorbed, burning through takes so long time.
It still does not explain why other materials are not turned into plasma on instant though.
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Post by bigbombr on Dec 27, 2016 10:53:13 GMT
I just figured out that something is very wrong with laser damage system - it looks like it always waits until the first hit object is destroyed, before damaging the second. You can armor ship with fused quartz against lasers and it is going to work fine, ignoring it's 96% trasmittivity against 265 nm light and you are trying to hide behind a ultra-fine glass window. Similar thing happens to aerogel, which is in fact very porous glass - it has 100% transmittivity, and since only extremely small fraction (I don't know if my calculation is correct, but it looks like it is 1.45e-9 of beam power) of the laser light is actually absorbed, burning through takes so long time. It still does not explain why other materials are not turned into plasma on instant though. This really should get fixed, as this drastically reduces the fidelity of the simulation. |
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Post by leerooooooy on Dec 27, 2016 15:29:22 GMT
The game fails at modelling laser damage in a vaguely plausible, let alone realistic, way.
There are bugs with transparency, targeting, ablation related damage, damage at steep angles...
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Post by Pttg on Dec 27, 2016 20:23:32 GMT
I kinda like my 10 gw kinda-near UV lazer. There's something about a 36 cm spot diameter at 1000km that brings joy to my heart.
Also multiple PJ/m in the sub-km range is entertaining.
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elukka
Junior Member
Posts: 73 
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Post by elukka on Dec 29, 2016 12:01:31 GMT
Yup, just boiling the material isn't enough. The vapour remains at the target site and is heated by over powered lasers, essentially protecting the unvapourised material for longer than it would at lower power density. However, with high enough beam power, the vaporized material will be a very high temperature plasma that will expand very quickly and very angrily to the point where its expansion will happily destroy anything around it. In other words, it causes an explosion. Further beam energy that arrives when the plasma is still present should add to its energy. Some will be lost as part of it will expand into space rather than the surrounding hull, but that extra energy should still add to its destructive potential. I'm mostly getting this from here: panoptesv.com/SciFi/LaserDeathRay/DamageFromLaser.php (I can't quite get the calculator to work, which is unfortunate.) Scroll down to the 'Deformation' section which has nice images and an explanation plus math of pressure-driven penetration. It does go a bit above my head so if something there is wrong I wouldn't really be able to tell. |
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Post by lieste on Dec 29, 2016 12:40:31 GMT
The calculator requires a non-zero atmosphere and also check what the ambient temperature should be. Obviously a radiator is more vulnerable to melt than an equivalent thickness of hull plating, which may be at single digit absolute temperatures (default is 300K)
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