This disclosure provides systems, methods and apparatus systems and methods described herein provide, among other things, a system for additive manufacturing of metal objects. The system includes two electron beams. In one optional implementation, one beam is high powered and acts as a deposition beam that melts a metal feed stock material which is delivered to a deposition zone and onto a work surface and the second electron beam is a low power electron source. The second electron beam acts as an interrogating source that generates an electron beam which interacts with the deposited material. The second electron beam may be active after material is deposited and provides post-deposition in-situ metrology. Various signals generated by this second beam/material interaction are collected and used to provide information about the melted and deposited material.