Flashlights and fallacies

Laser guns have been a staple of science fiction for almost as long as there has been science fiction - for longer, in fact, than we have had the word "laser".  The idea of using light as a weapon - clean, efficient and pure - has a particular hold upon the human imagination that no other "scifi" weapon seems to share.  Gyrojets and railrifles are popular with those of us at the outer edge, but it is lasers that everyone expects to see.

And, reliable as always when it comes to the recycling of familiar tropes, the 40kverse has them in abundance, particularly in the form of the Imperial Guard's favourite flashlight: the lasgun.  There's been some discussion recently on forums about how the lasgun works.  It's a popular topic and is sure to crop up again, but I thought I'd get some of my thoughts down while the topic was fresh in my mind.

First of all, it's worth saying that there are a number of different possible ways to achieve the typical effects described by various authors when it comes to lasweapons in the 40kverse.  What I suggest is just my way.  I make no claims to definitiveness.

I think it's worth starting by saying that I think that a laser has to be involved.  It's called a "las" weapon for a reason, so it needs to start with good old light amplification by stimulated radiation of emission.  Now, I'm no physicist, however much I might yearn to be one, but by my estimation, the laser in question needs to be a solid-state laser, with a crystal host, doped with something like Neodynium, as used in industrial cutting lasers.  To be a truly viable weapon as a laser alone, its power output would need to be mind-numbingly high for such a small weapon, though.  In addition, it would suffer, as all lasers do, from the "blooming" effect that disperses the coherent light when travelling through atmosphere, making the lasgun only effective at relatively short ranges, especially in dense atmospheres and fog.

Hence why I perceive the lasgunas more than "just" a laser weapon.  For a start, it is seen to possess natural recoil, to create a sound at muzzle-exit and to have an impact effect equivalent to a solid round.  This is why I argue for its being both a laser weapon and a particle beam weapon, albeit a fairly weak one.

Each pull of the trigger - when firing single shots - draws power from the magazine (which is really a battery) to create a laser with a peak output in excess of 3 kW or more.  The laser itself strips atomspheric atoms to align a particle beam of electrons that are propelled along magnetic rails in the barrel to follow the laser.  The accuracy of the particle beam is improved in good atmospheric conditions when it can follow the laser beam, and the laser impact will serve to enhance the impact of the particle beam, especially at low range before it can be affected by blooming.

This makes the lasgun a highly-effective assault weapon, in close quarter battle, and a serviceable rifle-analogue at longer ranges but a poor sniper's weapon.  This model would explain the recoil (caused by the particle beam) and the impact effects (likewise).  It would also explain the need for a barrel (the magnetic rails) and why sniper-models of the weapon such as the long-las require a longer barrel.  The larger size of such weapons and, of course, of weapons such as the lascannon can also then be explained by a more powerful battery pack (note the size of the pack carried by Space Marine scout snipers) delivering a more powerful laser that suffers less from blooming at longer ranges as a result of its greater power.

The lasgun would also possess a visible "bolt" of energy: the ionised particle beam.  Sniper variants at suitable ranges could potentially choose to "switch off" the particle beam to make use of the invisible laser alone where environmental conditions allowed.

The important thing to note is that the size of the battery dictates the range of the weapon, so a laspistol, with its smaller battery, has a shorter range than the lasgun or las carbine.  The length of the barrel then dictates the accuracy and power of the particle beam.