Well if anything was made it would probably be mounted on something big like a vehicle.
http://en.wikipedia.org/wiki/Directed-energy_weapon
Note there are many energy weapons not just lasers, you can have microwave, sound waves, electricity, radio, electromagnetic, plasma, etc. Its much more exotic than any sci-fi fantasy show. That's one reason I love real science sicne it is much cooler than anything seen in Hollywood movies.
I would really like to see some kind of sonic tank or mech that could blast their enemy with sound blasts be it pushing the air or just making them go deaf. Not to mention using it for seismic usages.
Yes, any energy weapon will do, wat ever you wanna call it, lasers, microwaves, what ever, same result in what im talkin about. I just say laser or plasma so the majority of people can understand the idea i am putting out there.
And yes, to start with it would be large and be mounted on a vehicle or mounted to the ground or wat ever other way you can think of, but large vehicles and mechs would be easy targets for air strikes, sat recon, rocket attacks, rpg and would be time consuming to set up, transport and the logistical cost would be high aswell. Production would be long and costly aswell plus it would take multiple people to operate it. The Military would try there hardest to miniaturise the weapon, just like they did for guns, so that infantry can use them.
the vehicle mounted weapon would work much like the first chariot unit does, bonus when attacking axe man. So the new weapon would have attack bonus on the future melee units, but be rather susceptible to the other attacks i described above. Then, once the weapon is miniaturised and infantry can carry the weapons, you have now progressed one more step in the evolution of weapons.
So, just forget the details of what to call the weapons or what type of energy, and just see the over all idea:
-stronger armor invented
-projectile wpns now obsolete
-strong close melee wpns invented to match strength of new armor
-first large scale longe range energy wpn capable of breaching armor from afar invented
-new armor is weak to this new weapon, but large scale wpn is weak to other conventional wpnry(rpg,missile,air strike etc.)
-large scale energy wpn is miniaturised for infantry
-new armor is now obsolete.
This happens over a period of perhaps 150 to 200 years and just a small part of the post modern era tech tree.
The main reason i thought of this was because alot of my friends that play RoM love it but usually stop playing after rifles become the main stream weapon. And from then on its guns and missiles, all the units look the same no matter what civ u are and they get bored cos they miss the variety of units and tactics they used. I personally dont mind, but i thought that if we could periodically along the future tech tree, reintroduce a reason for bringing back that melee style combat for a little bit, it would keep them playing knowing that combat will change again at later stages of the game and not just switch to guns and stay like that right into the future.