The first thing I need to do is point out that there is no such thing as a hotshot lasgun; what you’re describing is a modified charge pack that is designed to unload its entire charge in one shot.  The process burns up the inner workings of said charge pack, and often results in severe stress on the lasgun the charge pack is inserted into.  Needless to say, anybody who brings me a lasgun that has been torched by use of one of those charge packs gets a sound thrashing with said weapon before I will even consider repairing it.

Now, if we skip past the technical inaccuracies of your request, and boil it down to your general requirements, you’re asking me for something along the lines of a scaled down Hellgun.  This is problematic, and allow me to explain why:

The Imperium insists that all laser weaponry should operate within the visible spectrum of light; Guardsmen need to be able to see where their shots are going during combat so that they can adjust their aim accordingly.  The problem stems from the fact that visible light is very easily refracted by the various liquid vapors present in most forms of atmosphere, and greatly diminishes the amount of laser energy that actually reaches the target.  This effect is called “thermal bloom.”  Hellguns overcome this limitation through the use of sheer power, but the amount of energy required for this is exponentially larger - hence the backpack power supply.

There may be some potential in shifting the frequency of a laser weapon to something outside of the visible spectrum, but that sort of technology simply doesn’t exist right now; it’s something I’d have to research completely from scratch.