Polygonal Mirror Laser Scanning Heads: Characteristic Functions

The study analyzes Polygonal Mirror (PM) scanning heads for one of their most utilized setups: with an off-axis PM and the incident parallel laser beam orthogonal to the optical axis of the objective lens. The study places under the umbrella of the same theory systems that range from PMs with a small number of facets (e.g., industrial measurements) to PMs with a large number of facets as for high-end biomedical imaging systems, in particular for swept sources utilized in Optical Coherence Tomography (OCT). The characteristic functions of PM heads are derived: scanning function and velocity, pairs of rotational angles, and duty cycle. Two migration functions are also obtained, to characterize the displacement of the object point of the lens, as produced by the beam movement on the PM facet. Each function is studied with regard to the parameters of the PM head: number of facets, inner radius, rotational speed, eccentricity of the incident laser beam with regard to the PM pivot, as well as the distance from the beam to the lens. The theoretical results are validated experimentally. Considerations on the design of PM scanning heads are extracted from the analysis.