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Post by zuthal on May 23, 2017 9:55:14 GMT
Inspired by David367th 's laser science thread, I decided to do some more detailed investigations - specifically, in the relationship between laser intensity and burn rate. I started with aramid fiber because, well, it is one of the quintessential anti-laser armour materials, and decided to do it in the wide-beam limit (beam width much greater than laser wobble) and with a 77 nm Ce:LLF laser. It seems that up to a certain point, the burn rate increases linearly with intensity, only to then drop sharply again and get to a roughly constant value at even higher intensities - our standard "critical burn rate" value, which for aramid fiber is about 1.3 mm/s, from the data I have, giving it an anti-laser performance of 1.82 kg/(s*m^2) and 480.48 c/(s*m^2). What confuses me is this peak - is it just an artifact due to the measurement method, a glitch, or a real effect? |
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core2
New Member
Posts: 16 
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Post by core2 on May 23, 2017 15:52:39 GMT
Can you do this test for other common laser armors (si-aero, rubber, amo carbon) to see if its a specific effect to aramid or generally the case?
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Post by tukuro on May 23, 2017 18:20:43 GMT
5 MW/m² (77 nm Ce:LLF) is the optimal intensity against aramid fibre?
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Post by zuthal on May 23, 2017 21:42:03 GMT
Apparently yes, at least if you have a wide-beam laser, i.e. your aperture radius is a lot less than 12.4 cm.
And core2, I do plan on doing that - because while I would expect laser ablation rate to be sublinear with intensity, this is ridiculous.
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Post by goduranus on May 25, 2017 15:42:17 GMT
Didn't qswitched mention that vaporizing armor is a lot less efficient than melting the armor, in one of the blog posts, because vapor sends less heat to the layers beneath, while melted armor will heat up the layers below much faster.
Also if you don't change the output of the laser, the decrease could be due to the beam being too narrow to hit the same spot repeatedly, ie, the the illuminated spot being much smaller than the wobble of the laser.
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Post by michalo on May 25, 2017 18:23:44 GMT
Didn't qswitched mention that vaporizing armor is a lot less efficient than melting the armor, in one of the blog posts, because vapor sends less heat to the layers beneath, while melted armor will heat up the layers below much faster. Also if you don't change the output of the laser, the decrease could be due to the beam being too narrow to hit the same spot repeatedly, ie, the the illuminated spot being much smaller than the wobble of the laser. This is true I guess, but we can make lasers that achieve 321 EXAWATTS per m^2 intensity (at one km), which means putting 2.4 GW of power on circle with 86 microns radius. This also means that after about nanosecond, this spot will achieve temperature of about MILLION K, and start transmitting heat very effectively as different forms of radiation (thus not being any sort of armor anymore), and get diffused very fast. The laser would probably pierce the ship in microseconds or so, and should be able to simply cut it in half. |
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Post by zuthal on May 25, 2017 20:50:02 GMT
Also if you don't change the output of the laser, the decrease could be due to the beam being too narrow to hit the same spot repeatedly, ie, the the illuminated spot being much smaller than the wobble of the laser. I actually made sure that that wouldn't be the case - the aperture radius at which, for 77 nm lasers, the wobble is equal to the beam spot size (so it just barely always touches the same spot) is, according to my math, 12.4 cm. So, I made sure to always keep the aperture radius below 6.2 cm, ensuring that the laser would always cover at least one spot fully. |
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