On the map are three red lasers. One of them starts this bossfight. Every bossfight grants an achievement after completion.
To defeat this boss you have disable his shield first. To do this, find the shield generators, that are nearby on roofs and destroy them. You have a few seconds to damage him before he reactivates his shield. You can use pretty much any weapon because he doesnt move. You can make this fight trivial by setting the difficullity to Immortal and/or removing all enemy spawns.