The present disclosure relates to systems and methods that utilize an internal optical path in lidar applications. An example method includes causing at least one light-emitter device to emit a plurality of light pulses toward a rotatable mirror. The rotatable mirror (i) reflects at least a first light pulse of the plurality of light pulses into an external environment; and (ii) reflects at least a second light pulse of the plurality of light pulses into an internal optical path. The method also includes receiving, by a photodetector, (i) a reflected light pulse comprising a reflection of the first light pulse caused by an object in the external environment; and (ii) the second light pulse received via the internal optical path. The internal optical path is defined at least in part by one or more internal reflectors that reflect the second light pulse toward the rotatable mirror such that the rotatable mirror reflects the second light pulse toward the photodetector.