Ttyjukl

The space battles in the Expanse universe look very much like ship-to-ship (or plane-to-plane) fights from late XX and XXI century; they rely on expensive, guided torpedoes (that need to be shot in large quantities to get past the Point Defense guns), classical kinetic bullets, and occasionally a rail gun.

Yet the most popular SF weapon type - lasers - is missing. The technology is there: in the Slow Zone, when all kinetic weapons are neutralized, Belters manage to turn a communication laser into a weapon able to destroy other ships and (in theory)

even the alien station.

I remember, that engineer warns that this laser will melt to slag after a few seconds, but it is because this weapon is made basically from scraps. There is also no problem with power, since each ship is equipped with a large fusion reactor. If such a thing was properly developed, it would be much more viable - maybe not as a primary but at least as a decent secondary weapon. Yet they are not present at all.

Why?

Within the books, anti-personnel lasers exist in the Expanse universe and are sufficiently common that there are standard defences against them, notably gas grenades that fill the air with "anti-laser smoke" and "ablative" armour.

Anti-ship lasers are far less common and are basically a known technology but one that is used infrequently since they're a) energy-hungry and b) largely useless against anything other than an unarmoured civilian ship (which you could just blast with a railgun and save yourself the trouble.).

The service corridor they’d cut into was narrow and dim. The
schematics the Tycho engineers had worked up suggested they wouldn’t
see any real resistance until they got into the manned parts of the
station. That had been a bad guess. Miller staggered in with the other
OPA soldiers in time to see an automatic defense laser cut the first
rank in half.

“Team three! Gas it!” Fred snapped in all their ears, and half a dozen
blooms of thick white anti-laser smoke burst into the close air. The
next time a defense laser fired, the walls flashed with mad
iridescence, and the smoke of burning plastic filled the air, but no
one died. Miller pressed forward and up a red metal ramp. A welding
charge flared, and a service door swung open.

_{^{Leviathan Wakes}}

and

The first thing that went on was what the grunts called the full-body
condom. It was a thick black bodysuit, made of multiple layers of
Kevlar, rubber, impact-reactive gel, and the sensor network that kept
track of his injury and vitals status. Over that went the slightly
looser environment suit, with its own layers of self-sealing gel to
instantly repair tears or bullet holes. And finally, the various
pieces of strap-on armor plating that could deflect a high-velocity
rifle shot or ablate the outer layers to shed the energy of a laser.

_{^{Caliban's War}}

While lasers are inherently cool, their practicality as a weapon is greatly curtailed by several factors

First, applying a reflective coating to a ship, or plating the hull in a high melting point metal such as tungsten, would reduce their effectiveness greatly.

Second, lasers are a line of sight only weapon.

Third, unless you make a laser extremely powerful, it has to stay focused on a small area for a prolonged period of time to actually do damage. This would be difficult if the laser was fired from a moving platform at a moving platform over the distance of several kilometers.

TL;DR

Ultimately lasers are not present, as large scale weapons because the military's decided their flaws outweighed their virtues.

I love The Expanse, but it think that it fails at about this. The only reasonable argument against Lasers is their low power, but we are talking about a background of extremely developed power sources. If even today we already have Laser weapons in use by US and Russia, with some minor results, there is no reason to assume that dozens of years in future these weapons would not be much more powerfull and efficient.

One major problem to our actual Lasers is atmosphere, that severely reduces is range, but it will not a issue in space. But the main reason I believe that Lasers will be much more usefull in space than guns is speed. We are talkin about situations of extreme velocity e very large distances, covered by high powered sensors.

How fast a bullet or a missile can fly? It extremelly unprobable that they can come close to light speed, so, about 100.000 km, they can be detected much before they come, allowing evasive actions. If have defensive Lasers, the ship can easily destroy the missiles and dodge the bullets. By the other hand, obviously, a Laser shot can't be detected before it comes!

So, except if is assumed that higher powered Lasers are not possible, what I think quite unprobable, bullets and missiles has no chance against Lasers!

I have two texts specifically about this. But they are on portuguese.
http://xr.pro.br/FC/BATALHAESPACIAL.HTML
http://xr.pro.br/FC/BATALHAESPACIAL2.HTML