Ultra-short duration pulse lasers

[GURPS Fox]

So, I've been investigating how GURPS treats pulse lasers and it has been enlightening, but sad. For one, there is no way to simulate pulse lasers at the micro to pico-second duration range and another has me finding out that it is spread over the overall output and not per-pulse. The only rules for pulse lasers are that if RoF is greater than or equal to 4 does the damage double and a change of damage type. Energy requirements stay the same, no additional modifiers, that sort of thing.

This is at odds with the pulse lasers that I've been planning to use in my future-history setting where they're triple-digit microsecond pulses, meaning that a 1GJ/pulse laser (the smallest anti-ship laser in one faction's arsenal) requires 4TW of electricity to function.

So how would I stat such lasers in this regard?

[Ulzgoroth]

Originally Posted by GURPS Fox

So, I've been investigating how GURPS treats pulse lasers and it has been enlightening, but sad. For one, there is no way to simulate pulse lasers at the micro to pico-second duration range and another has me finding out that it is spread over the overall output and not per-pulse. The only rules for pulse lasers are that if RoF is greater than or equal to 4 does the damage double and a change of damage type. Energy requirements stay the same, no additional modifiers, that sort of thing.

This is at odds with the pulse lasers that I've been planning to use in my future-history setting where they're triple-digit microsecond pulses, meaning that a 1GJ/pulse laser (the smallest anti-ship laser in one faction's arsenal) requires 4TW of electricity to function.

So how would I stat such lasers in this regard?

...Where are you finding the only rule you're finding?

You should also look at the rule on Ultratech p118-119.

However, the way you're describing it seems rather weird. A pulse laser isn't necessarily (or likely, I should think) emitting a pulse train with no breaks!

There are some sources (well, at least one) for probably more realistic treatments of lasers than GURPS standard, but I'm not sure realistic is what you're looking for here... EDIT: Though you would need to back-convert from material effects to GURPS damage.

[GURPS Fox]

Originally Posted by Ulzgoroth

...Where are you finding the only rule you're finding?

You should also look at the rule on Ultratech p118-119.

So far, largely yes when using 3e. There are no modifiers for pulse lasers in terms of energy input in kW or joules (at least, that I could find), which I find weird as hell, for the moment you start shrinking the duration, the higher your energy input requirements.

However, the way you're describing it seems rather weird. A pulse laser isn't necessarily (or likely, I should think) emitting a pulse train with no breaks!

There are some sources (well, at least one) for probably more realistic treatments of lasers than GURPS standard, but I'm not sure realistic is what you're looking for here...

Did some digging with what I've got and at the GURPS discord and that's how I found out that pulse lasers are output over the duration and not per pulse.

The pulse lasers I'm usually used to in their descriptions have been output per pulse, not overall output. Add to that the descriptions having 'cycles' -i.e. how many times a laser goes on and off- as well, and thus wanting to port this over.

So far I've been thinking of using a 'per cycle' damage (so, a 1GJ/pulse laser that has a 16-pulse per cycle would thus have an output of 16GJ) instead of the usual damage figures.

[Anthony]

Originally Posted by GURPS Fox

So far, largely yes when using 3e. There are no modifiers for pulse lasers in terms of energy input in kW or joules (at least, that I could find), which I find weird as hell, for the moment you start shrinking the duration, the higher your energy input requirements.

Not unless there's an efficiency drop. GURPS treats a chain of multiple pulses in a short period as a single shot.

[whswhs]

Originally Posted by GURPS Fox

So far, largely yes when using 3e. There are no modifiers for pulse lasers in terms of energy input in kW or joules (at least, that I could find), which I find weird as hell, for the moment you start shrinking the duration, the higher your energy input requirements.

I don't see why. If you deliver a GJ over one second, you have a power of 1 GW while it's on. If you deliver it over one millisecond, you have a (much briefer) power of 1 TW. But the total energy delivered is still 1 GJ. It just arrives more all at once.

[GURPS Fox]

Originally Posted by Anthony

Not unless there's an efficiency drop. GURPS treats a chain of multiple pulses in a short period as a single shot.

Something that I gathered in my investigations... but all my investigations don't have the lasers in the micro/nano/picosecond duration range.

Especially when a joule per 500ns (nanoseconds) is 2MW... and just having a laser in the microsecond range has something on the order of 1-joule per 500m microseconds being 2kW...

Given that damage only increases when RoF of a pulse laser is 4 or more (ignoring the effects of ultra-short duration pulse lasers that the scientific community has been putting out)...

[GURPS Fox]

Originally Posted by whswhs

I don't see why. If you deliver a GJ over one second, you have a power of 1 GW while it's on. If you deliver it over one millisecond, you have a (much briefer) power of 1 TW. But the total energy delivered is still 1 GJ. It just arrives more all at once.

From what I can tell, that isn't exactly the case. Especially as you get to ultra-short durations.

[Sam Baughn]

What's the purpose of an ultra-short duration laser pulse for a weaponised laser? I was under the impression that the main purpose of pulsing a high-energy laser weapon was to allow the debris (plasma, hot gas, vapour, molten droplets, fragments) generated by blasting the surface of the target to clear out of the way, so that the next pulse would hit the bottom of the crater created by the previous one and so eventually drill deeper than just using the same energy as a steady beam. But that seems to requite micro-second pulses rather than pico-second ones, which would surely be too quick to actually let the stuff move far enough (although I suppose at very high energy densities, stuff moves quicker, so really big lasers might want to pulse faster).

[whswhs]

Originally Posted by GURPS Fox

From what I can tell, that isn't exactly the case. Especially as you get to ultra-short durations.

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

[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.

Originally Posted by GURPS Fox

From what I can tell, that isn't exactly the case. Especially as you get to ultra-short durations.

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.