Abstract: A smoke concentration measurement system includes: a beam extension chamber having a body defining a smoke channel having a longitudinal axis, the smoke channel having a smoke inlet and a smoke outlet at opposite ends of the longitudinal axis, a first reflective surface located on a first lateral side of the longitudinal axis, an entrance window located on the first lateral side of the longitudinal axis, a second reflective surface located on a second lateral side of the longitudinal axis, and an exit window located on the second lateral side of the longitudinal axis. The system also includes a laser light source adapted to emit laser light onto the entrance window, the laser light reflecting back and forth between the first reflective surface and the second reflective surface toward the exit window, and a first light measurement device adapted to receive laser light exiting the exit window. Other features, as well as a method of measuring the concentration of smoke, are also described.