Ultra-short duration pulse lasers

[Fred Brackin]

Originally Posted by whswhs

It sounds like the math is wrong, but I would need to see the actual calculation.

Concentrating all the energy into a shorter pulse should probably get you a higher armor divisor as it becomes harder for material substances to resist even briefly. It shouldn't do more HP though.

[whswhs]

Originally Posted by Fred Brackin

Concentrating all the energy into a shorter pulse should probably get you a higher armor divisor as it becomes harder for material substances to resist even briefly. It shouldn't do more HP though.

Yes, but "the energy has greater effect if it's delivered quickly" doesn't equate to "more energy was delivered."

[GURPS Fox]

Originally Posted by Fred Brackin

Concentrating all the energy into a shorter pulse should probably get you a higher armor divisor as it becomes harder for material substances to resist even briefly. It shouldn't do more HP though.

Didn't think of that...

Originally Posted by whswhs

Yes, but "the energy has greater effect if it's delivered quickly" doesn't equate to "more energy was delivered."

From what I understand, the shorter the duration, the more devastating the pulse is, to the point that it would resemble something from a far more powerful laser.

At least that's what the article implied.

Originally Posted by Ulzgoroth

FYI, it's generally recommended to flag when your topic is 3e. Otherwise people will usually assume that we're working with the current edition instead.

Sorry about that... didn't know.

Nothing at all related to what whswhs said would change at all with 'ultra-short durations'. It's just power = energy / time.


A pulse laser has a pulse power, which is pulse energy/pulse duration, and an output power. Output power will always be less than pulse power, because it's not a pulse laser if it's emitting 100% of the time. It can be much less. A laser that shoots a picosecond pulse could perfectly well shoot only one such pulse per second.

From what I understand, it's kind of both? I'm very fuzzy on the specifics in that but from what I understand (and remember) the shorter the duration, the more the effects change. The more likely things like impulse shock happen, the more penetration it can get with various materials, so on and so forth.

[Ulzgoroth]

Originally Posted by GURPS Fox

From what I understand, the shorter the duration, the more devastating the pulse is, to the point that it would resemble something from a far more powerful laser.

...Seems unlikely, as such. It might be more damaging, but it won't be more damaging in the same way as if you'd just stepped up the power.

And regardless of whether the same energy in a shorter pulse causes greater damage, it doesn't stop being the same energy!

Originally Posted by GURPS Fox

From what I understand, it's kind of both? I'm very fuzzy on the specifics in that but from what I understand (and remember) the shorter the duration, the more the effects change. The more likely things like impulse shock happen, the more penetration it can get with various materials, so on and so forth.

Very short pulses as I understand it cannot have high penetration. They cause explosive cratering, which expands to the sides at least as much as it pushes inward.

Chains of very short pulses in quick succession, hitting in the same place, can cause penetration by each successive pulse cratering the bottom of the crater from the preceding pulse.

[Anthony]

Originally Posted by GURPS Fox

From what I understand, the shorter the duration, the more devastating the pulse is, to the point that it would resemble something from a far more powerful laser.

You get somewhat different penetration mechanisms, but ultrashort pulses are actually prone to wasting energy superheating a very narrow surface layer. The main reason to use ultrashort pulses is if you want to take advantage of atmospheric self-focusing.

[GURPS Fox]

Originally Posted by Anthony

You get somewhat different penetration mechanisms, but ultrashort pulses are actually prone to wasting energy superheating a very narrow surface layer. The main reason to use ultrashort pulses is if you want to take advantage of atmospheric self-focusing.

From what I understand, that's not exactly the case, especially when you go to the shorter wavelengths (i.e. UV and X-Ray)... but I've lost the links to the articles (constantly changing internet can make things vanish).

[Anthony]

Originally Posted by GURPS Fox

From what I understand, that's not exactly the case, especially when you go to the shorter wavelengths (i.e. UV and X-Ray)... but I've lost the links to the articles (constantly changing internet can make things vanish).

The basic problem is that it takes a while for material in the path of your beam to move out of the beam, and while there's an upper limit to how much energy it can absorb, that upper limit is very very high. Thus, the normal drilling mechanism is 'apply energy, wait for the superheated material to exit the hole, repeat'; you can add more energy to get the material out of the hole faster, but doing so is extremely inefficient. Short wavelength penetrating radiation lets you heat a thicker layer at every pulse but doesn't otherwise evade this fundamental limit.

[Ulzgoroth]

Originally Posted by Anthony

The basic problem is that it takes a while for material in the path of your beam to move out of the beam, and while there's an upper limit to how much energy it can absorb, that upper limit is very very high. Thus, the normal drilling mechanism is 'apply energy, wait for the superheated material to exit the hole, repeat'; you can add more energy to get the material out of the hole faster, but doing so is extremely inefficient. Short wavelength penetrating radiation lets you heat a thicker layer at every pulse but doesn't otherwise evade this fundamental limit.

According to this, they actually can at the extreme end of the scale, because superheating the material apparently makes it become transparent to some radiation around the x-ray range. So the beam doesn't have to wait for the material to get out of the way, only for it to get hot enough.

[GURPS Fox]

Originally Posted by Anthony

The basic problem is that it takes a while for material in the path of your beam to move out of the beam, and while there's an upper limit to how much energy it can absorb, that upper limit is very very high. Thus, the normal drilling mechanism is 'apply energy, wait for the superheated material to exit the hole, repeat'; you can add more energy to get the material out of the hole faster, but doing so is extremely inefficient. Short wavelength penetrating radiation lets you heat a thicker layer at every pulse but doesn't otherwise evade this fundamental limit.

Yeah, one of the things I remember is that 'after a certain point, pulse lasers don't look like lasers but kinetic weapons in terms of damage'...

Originally Posted by Ulzgoroth

According to this, they actually can at the extreme end of the scale, because superheating the material apparently makes it become transparent to some radiation around the x-ray range. So the beam doesn't have to wait for the material to get out of the way, only for it to get hot enough.

Interesting... then again, from what I've gathered, UV wavelengths also have that ability, as they can penetrate plasma sheaths of hypersonic objects (like, say, hypersonic missiles or reentry vehicles...).

[Ulzgoroth]

Originally Posted by GURPS Fox

Yeah, one of the things I remember is that 'after a certain point, pulse lasers don't look like lasers but kinetic weapons in terms of damage'...

Note though that that's not a statement of their great penetration. Hypervelocity kinetic weapons deliver a huge amount of energy but don't convert it to penetration well. They explosively crater on impact instead of being able to stab into the surface.

Originally Posted by GURPS Fox

Interesting... then again, from what I've gathered, UV wavelengths also have that ability, as they can penetrate plasma sheaths of hypersonic objects (like, say, hypersonic missiles or reentry vehicles...).

If you look inside the link, it describes the relevant wavelengths as "vacuum ultraviolet, extreme ultraviolet, and soft x-ray"