The physical expression of this in a space scenario is called a "Matter Beam", and it is just what it sounds like.
This has been proposed for various uses, mostly as a method of spacecraft propulsion, but any device capable of transferring momentum on that scale can most certainly be used as a weapon as well. Taking your matter beam "emitter" up to "11" gives you the sort of concentrated beam of physical particles which can cause serious damage to the enemy spacecraft.
The mechanism is kinetic energy (Ke=1/2 MV^2), and each particle can carry a considerable amount of energy simply by virtue of moving at interplanetary speeds. An object moving at 3km/sec (fairly slow by interplanetary speed standards) will have an energy equal to its wight in TNT. Colloquially, this is known as "1 Rick" of energy. Since objects can be accelerated to 72 km/sec before they are no longer bounded by the Sun's gravity, you can pack a lot of "Ricks" into a stream of postage stamp or smaller sized particles. A full set of calculations is in the ever handy Atomic Rockets "Conventional Weapons" page.
Now the downside of all this is you need some pretty impressive hardware if you are going to saw through an enemy spacecraft. From Atomic Rockets:
As an example, suppose we have a synchronous coilgun, and that the coilgun can generate 1 tesla fields (a good number that will not saturate the ferromagnet). Our presumed ferromagnet is probably mostly iron, with about 8000 kg/m3. To reach 100 km/s, you will need 40 TJ per cubic meter of projectile. Since this is 100 million times the energy density of the field, you will need the projectile to sweep out 100 million times its volume in order to accelerate up to the desired speed. This means you need an accelerating track 100 million times the length of your projectile. If the projectile is the size of a dime, with 1mm thickness, you will need a 100 km long track. If 2.5% of the energy goes into the projectile as heat as a result of inefficiencies, you get 100 GJ of heat per cubic meter of projectile, or 12 MJ/kg. This is three times the specific energy liberated by detonating high explosives, so you can expect your projectile to explode like a bomb inside your coilgun barrel. Consequently, this appears to be an unworkable design.
So how do we get a compact, "workable" design?
Fortunately, the same page also discusses the use of nuclear weapons as compact, high energy power sources for projectile weapons. A nuclear "shotgun" can potentially accelerate pellets to 100 Km/sec. While this isn't going to saw through a ship, it will certainly cause a lot of damage.
A nuclear "Shaped Charge" can potentially accelerate a stream of liquid metal to @ 3% of c. You won't get a cut like a saw, but a hole drilled through armour, shielding, ships systems and anything else caught in the path of the stream.
A Casaba Howitzer accelerates a spindle shaped plasma to @ 10% of c, so evading becomes quite difficult. Once again, sawing through a ship might not be possible, but the damage could be similar to a high energy laser.
Finally, a large enough laser could do just what you want. On the Atomic Rockets page, Luke Campbell has done some rough calculations for a Free Electron Laser (FEL) capable of vaporizing metal and ceramic at a range of one light second, 300,000 kilometres, almost the distance from the Earth to the Moon. This Ravening Beam of Death (RBoD) will be capable of cutting through most ships (although there will be a time factor), and even when not slicing through ships, could have a "scorch" range of up to a light hour.
X-ray laser RBoD. The ultimate in firepower
To put that in perspective, the accelerator for the FEL will need to be a kilometre long, but when you absolutely and positively need that sort of firepower.....