A furnace and method for the cracking of hydrocarbons. The optical measurements may be individual power measurements taken for each light-path at various points in each node it traverses, such as amplifiers, multiplexersdemultiplexers or at an interface with another node. A partition with a plurality of perforations is provided in the chamber to separate the fluid into fluid segments. An isolation circuit is coupled to the first cell, the second cell and the low power circuit to maintain a current isolation between the first cell and the second cell at least during delivery currents having a large magnitude that are delivered to the high power output circuit.