Analysis of polygonal mirror scanning heads: from industrial to high-end applications in swept sources for OCT

Abstract

An analysis of polygonal mirror (PM) scanning heads has been performed, in order to provide a tool for their optimal design. The theory developed brings under the same umbrella applications that range from industrial dimensional measurements to high-end biomedical imaging, for example for broadband laser sources swept in frequency for Swept Source Optical Coherence Tomography (SS-OCT). The different characteristic parameters of the PM scanning heads were considered in order to achieve a rigorous analysis: number of PM facets, inner radius of the PM, eccentricity of the PM pivot with regard to the incident fixed laser beam, distance from this beam to the principal plane of the objective lens, and angular velocity of the PM. The functions that characterize the PM scanning head have been deduced: scanning function and velocity, characteristic angles, duty cycle, and two migration functions (longitudinal and transversal) that allow for an optimized designing calculus of the PM placed in different SS configurations. The analytic and numerical analysis of these functions has been performed with regard to the characteristic parameters of the scanning head. Experimental validations of the theory were further completed. While the above analysis has been carried out for a characteristic ray of the collimated laser beam (i.e., its central axes), it also allows for considering in a simple way the finite diameter of the beam. Thus, a discussion on the deformation of the beam – as produced by the eccentric rotational PM facet – can also be perfomed. A comparison of the PM scanner with the most common types of laser scanners highlights its advantages and drawbacks for OCT.