OK, back to the whole Aerial Balistic Laser (ABL) thing. Yes, the ABL is chemical based, but whoever said it doesn't take much energy to use is dead wrong. It doesn;t take much electrical energy, but it takes a TON of chemical energy. Basically the ABL is a modified chemically pumped laser, similar to common neodymium yag lasers or a CO2 lasers, just much much much larger.
It should be noted that the main issues with laser based weaponry are 1. Power (as in deleivered energy to the target), 2. Penetration time (time it takes the beam to penetrate/damage the target), and 3. Countermeasures.
Issues #1 and #2 are directly proportional to one another as a higher power laser will penetrate a target faster then the same laser at lower power. Therefore it is obvious that for the purpose of weaponry, high power is desirable. The issue with chemical lasers or lasers in general is that they require a tremendous amount of energy to excite the light amplifying medium so that a sufficient number of photons can be generated to actually damage anything. That energy has to come from somewhere, and in chemical lasers its generated by a chemical reaction (as opposed to electricity), that generates heat is used to exite the light amplifying medium, after which enormous amount of light energy can be extracted from the medium. This type of laser is well documented, with HF based chemical lasers being the most powerful (as the reaction of H with F is one of the most, if not the most exothermic reactions known to man).
Bearing the above points in mind, It shoudl ebe noted that in order for a laser based weapon to be effective it must be capable of delivering damaging amounts of energy to the target at range. Therefore, you have to take into account the fact that a collimated beam of light diffuses over distance (shine your laser pointer at a wall 3 feet away and the dot size is maybe .5cm, shine it at a wall 300 feet away and it will be significantly larger). As the spot size gets larger, the amount of transferred energy a specific area of the target goes down, and thus penetration time increases.
One way to ensure that you have enough power delivered to the target is to, you guessed it..... make the laser more powerful. How do you make a laser more powerful by using the same reactants? You guessed it... use more reactants! If you research the ABL, you'll see that it is only capable of firing a few times before its chemical stores need to be replenished. Also, you'll note that the laser is only capable of penetrating a missile hull in a few seconds. Now a few seconds may seem short, but when you consider the average modern missile flies well over 600 miles an hour, you need one hell of a tracking system to be able to maintain a beam spot (which in the ABL is only a few cm mind you) on the exact same portion of the target for 2-3 seconds at least (more if the hull is thicker). Thats why the ABL is still being researched and is in fact not being widely used.
The other issue is countermeasures. Someone earlier asked if coating a target with a reflective surface would render laser weapons ineffective. The answer is yes.... to some degree. As I'm sure you are all well aware a laser beam is simply massive amounts of photons that are emitted in the same direction at the same wavelength. Thus, should some commie spy discover the wavelength our laser weapon fired at, conceiveably they could coat a target they wished to protect with a substance specifically designed to reflect light at that wavelength. However, unless the reflective surface was 100% reflective at that wavelength (unlikely as dust, fingerprints, etc. on the surface of the reflector will result in some absorbtion), if given sufficent power/time the laser would eventually penetrate the coating, especially in the case of high power chemical lasers, which are generally high power IR lasers that impart a large amount of thermal energy to the target and thus over time would likely destroy the reflective coating unless the coating was particularly heat resistant.
That said, I think the most effective future weapon would be space deployed GPS guided napalm canisters. Nothing would deter me more from crime/terrorism then the possibility that a flaming ball of death could be hurled at me from anywhere on the globe as punishment.