The present disclosure relates to systems and methods that provide an accurate angle measurement of a rotatable mirror. An example method includes receiving, from a detector device, a reflected light signal. The reflected light signal is indicative of primary reflection light and secondary reflection light. The primary reflection light corresponds to a first portion of emission light that reflects directly from the reflective surface of the rotatable mirror toward the detector device. The secondary reflection light corresponds to a second portion of emission light that: 1) reflects from the reflective surface of the rotatable mirror toward a secondary mirror surface; 2) reflects from the secondary mirror surface toward the reflective surface of the rotatable mirror; and 3) reflects from the reflective surface of the rotatable mirror toward the detector device. The method also includes determining, based on the reflected light signal, the rotational angle of the rotatable mirror.