I personally do not like lasers for space combat settings, probably more because it is not enough space in the ways how they are usually described or used, but let's attack your perception that they are always boring.
Dragongeek mentions nuclear-pumped laser, good stuff, buuut...
Expand! Engage! Bigger! Better! Make it so!
- make it soo big that u eyes are popping out from how big it is, space is big, keep your eyes in a pocket and fly safely.
There are certain problems with the implementation of the idea, so it just an idea.
Space is big and empty, very convenient for fusion things, I mean typical attempts to make fusion work spend a great deal of effort to make a vacuum close to one which is present in unlimited quantities in space.
So imagine a gas(plasma) cloud (yes, I like gas clouds in space) in a form of a cylinder, with a diameter of 1-2 km and length of 1000 km. Which consist of some fusion mix maybe plus something, but not necessarily.
If you manage to blast that cloud, ignite it in a fusion way, it will create a plasma cylinder, maybe 10 km in diameter in the time when it was used (obviously it will dissipate after a short time) but for a few milliseconds it is there for our use.
It will be high energy plasma high excited state, it is what lasers use in their optical cavities so it is a thing which a laser needs, and a flash on one end in direction to another end will collect some energy, will be amplified by going through that plasma cloud and on the other end, as it exits the cloud it may have substantial energy.
It does not need an optical cavity, a distance a photon goes bouncing forth and back in some 10cm rod is maybe a few times less than those 1000km soo straight through is enough. (Not enough? Make it 10'000, 100'000, a million km)
ITER plasma energy/power density is something around 1MW per cubic meter of plasma, it is energy produced per second, soo let's say our plasma cloud exists, in its useful state shape form properties, for 5 ms, soo about 5000 J of energy per cubic meter are "produced" in those 5ms, let say the efficiency of extracting energy out of it with our amplified pulse is 1% (it probably should be more, but..), so we get 50J per cubic meter on the exit side.
2km diameter, 1000km length yields about 3 TJ of energy, contained in a 5ms pulse.
- it 25 times more for that 10 km diameter I initially proposed. Why scaling down, idk, it is a complex dynamic expanding situation, so to be conservative
Not much, especially compared to the size, and diameter of the beam, but it lands us in one kiloton of TNT territory for the pulse. And if we use a reactor on a ship to do the same it has to reach peak power of 600'000GW × 1/efficiency, or if we have some ability to pump the energy for a minute, and it sounds easier than it practically is as we have to store energy somewhere and at the end, we have to deliver it fast to some optical cavity then it is 50GW × 1/efficiency.
- as of today, 50GW is quite a challenge and the thing isn't small, and if efficiency is 10% it then 500GW to shoot once in a minute. 500 reactors, eh.
Thinking about that, a typical depiction of a laser installed in a ship is sooo wrong, sooo unrealistic from a technology perspective.
In general, any high-energy weaponry or even devices or even the main characteristic of a space ship its engines installed next to crew and other ship internals is not necessarily the way to go.
- The Expanse handwaved its Epstein drive, which by the specs is nothing but a regular fusion engine, but done in a right/wrong/realistic way then things would look nothing like it was depicted in the show, not even close. (Like their missiles, lol)
- this expanse example probably is an addendum to the point - maybe things are boring because they are wrong and stuck to concepts of the 70's - weapons inside a ship, engine inside a ship, etc. Here a guy asked about heat dissipation for his ships, a right question How to get rid of all the heat in my spaceship? and the short answer is to not allow to build it up where it should not. And in that sense, external components are a perfect solution, engines, weaponry, and stuff. So a ship is not necessarily a ship as it was envisioned since the '70s as monohull construction but a cluster of components, deployed temporarily or always external.
In the case of that plasma cloud, we have problems - it dissipates, how to ignite it, how to recharge, or how to set up it in the first place.
In that sense, we can have a series of devices, in different configurations and function, not one solid block of a reactor of that size, but as separate units, like those cool stargate rings type every 1000 meters apart, which each of those we deploy out of cable/pipe/whatever 3.5-7 km long. These are, components, deployed from some ship, it is its external temporary device, which can have different stages of deployment for ease of manipulation with that equipment. And in the end, it is a somewhat open big fusion reactor that pulses for a minute(or how much it can take by design +50% to be more dramatic) each second making our 5 ms bangs, then some cooldown time, which can be speedup by some another deploy component.
- that ring setup for that temporary fusion reactor is not necessarily the best way to do it, it can be a set of devices in its core as well(there are ways for that) and it may be a better way. But what best is probably beyond the point I try to conduct, and you were so generous with you restrictions soo
- also magsail designs are quite interesting concepts of small devices affecting plasma, solar wind, at distances of 10's km. (There should be a link, but, someone plz)
So instead of those useless carriers motherships which look so cool in the movies where main characters with cool faces jump in their fighters to do phue phue phue against bad guys. A ship deploys a unit that does the bang, which has the potential to obliterate things. With those fighter guys, especially on the distances and with those pointless actions they typically do, few nukes is enough to wipe them all clean, they were pointless since the inception.
Some guy proposed to use sun's corona as the laser medium, no containing problem, should probably work well, obiviously it has its limitations as well. So really, more space thinking and things start to become fun again. What you typically see are old concepts reused over and over again because yeah you know reasons, lol.
Where to get all those fusion components u waste so much each shot. Go to Jupiter, there is enough for hundreds of pan-solar wars.
Okay okay maybe this laser thing isn't great in a long run, really worse than a steam engine, but imagine those guys from a fleet of carriers, they are about to do their pheu pheu usual stuff, and you enroll your shiny reactor thing for the first time for actions and bang bang, and then laugh at their debris muhaha, they even didn't have the time to deploy.
This superiority will hold until the next good thing or until they build one for themselves, or effective countermeasures can be implemented. Countermeasures are inseparable from the capacities of your fleets, so you may figure out one quite fast(but that guess may turn out to be the wrong one) but not necessarily be able to implement, so it not instantaneous if one lacks capacities.
There always will be a next good thing, nothing set in stone.
In a sense your first question is good but not for an attacking purpose, but how to transmit energy in form of electricity in a compact way/easy to use directly between components in space which are km's apart without using wires. Those fancy plasma beams between components occasionally popping up, and they do make practical sense in some settings.
That macron thing is quite good actually, you can use it to set up cloud, like dynamic 3d printing, D-icicle particles at different velocities and angles to melt and slowly to evaporate, and to ignite the cloud later. Soo, there is more than one way to skin a fish.