Flamer

A power-armored trooper in the Imperial Army using a handheld flamer to destroy a heretical church

A Flamer is a slang term for a hand-held weapon that uses powerful infrared-band diode lasers in conjunction with a microwave-band klystron emitter to heat up a target rapidly to the point of ignition.  An advanced alternative to traditional flamethrowers, by eschewing flammable liquids or gasses, a flamer avoids the danger of carrying around a huge tank of pressurized explosives strapped to your back through a combat zone.  Short-ranged due to atmospheric absorption and diffraction, as well as the spreading effect of their usual wide-angle arc of fire, they are mostly used as a secondary weapon for destroying structures and materiel, as well as taking advantage of the fact that many magickal creatures, such as werecreatures and vampires, are far more vulnerable to fire than they are to mere physical trauma such as inflicted by bullets.  As such, many types of Power Armor carry a Hand Flamer built into one or both gauntlets, and many small arms designed to be used by power-armored troopers have a flamer attachment under the main barrel. 

Flamers are not particularly useful against soldiers in power armor or armored vehicles in general, but the combination of infrared surface heating and microwave internal heating will ignite most flammable materials within the arc of fire, and cause heat-related stress fractures or other structural weakening in most other materials.  Like plasma grenades, flamers can easily trigger out-of-control fires which, depending on the combat terrain, can be either disastrous (dry grasslands) or inconsequential (rocky desert).

Behind the Scenes

Based on the weapons used in the original Starship Troopers novel. Technobabble explanation partly inspired by a weapon from the game Crysis.