No discussion of futuristic small arms would be complete without examining the most famous, Star Trek’s phaser.
Deciphering desciptions on various official Star trek websites, a phaser appears to be an extremely sophisticated form of particle beam powered by an insanely potent power source (one source cited a hand phaser’s battery holding 1.3 million megajoules worth of energy per cubic centimeter—and this is all in a machine no bigger than a squirtgun!) How this beam affects a target depends very much on how much energy is pumped into it, and these weapons can pump a LOT of energy into a single shot.
The particles in a phaser’s beam are referred to as "rapid nadions," as-yet fictional meson-like particles that cause interference, or disruption, effects in atomic nucleii. At very low energy levels, these beams can only disrupt low-level electromagnetic fields, and as such interfere with the function of the electrochemicals in a living creature’s nervous system, hence their "stun" effect.
At median levels, the phaser acts very much like a conventional particle beam, delivering primarily heat damage to a target. This heat transfer can simply warm up an object (as in one episode where the crew used their phasers to make rocks glow for heat in a wintery environment,) cause it to blast apart, or even completely incinerate a human-sized target.
At the higher levels of the beam’s output, the "rapid nadions" affect the particles in an atom’s nucleus directly, causing them to fly apart, or disintegrate, in an intense chain reaction that converts most of the mass into nuetrinos, accompanied by a bright flash of radiation. According to some of the specs, a hand phaser on its highest setting could disintegrate up to 650 cubic meters of matter in a single shot. Basically, no material armor, no matter its composition or configuration, could withstand a phaser weapon at these settings, with the possible exception of collapsed matter (ie, neutronium.)
Phasers as hand weapons appear to have no upper limit on effective range, beyond what its human operator can reasonably hit (about 30 meters for hand phasers, several hundred to a thousand meters for a phaser rifle.)
Hand phasers in the various Star Trek series were designed for maximum possible versatility, with a wide range of beam options (wide beam, rapid-fire, continuous beam, etc) in an exremely compact and lightweight package. As would only make sense, to give groups of explorers a maximum number of possible solutions to unforeseen problems.
Phaser Rifles are dedicated combat weapons. Phasers rifles are stabilized via a shoulder stock for longer range shots, are more rugged, possess auto-aim features, and have much larger power reserves.
| L: Phasers firing at a shielded target
R: An unfortunate target experiencing the disintegration effect
All images (c) Paramount