# Optomechanical Analysis and Design of Polygon Mirror-Based Laser Scanners
###### Abstract  
Polygon Mirror (PM)-based scanning heads are one of the fastest and most versatile optomechanical laser scanners. The aim of this work is to develop a multi-parameter opto-mechanical analysis of PMs, from which to extract rules-of-thumbs for the design of such systems. The characteristic functions and parameters of PMs scanning heads are deduced and studied, considering their constructive and functional parameters. Optical aspects related to the kinematics of emergent laser beams (and of corresponding laser spots on a scanned plane or objective lens) are investigated. The PM analysis (which implies a larger number of parameters) is confronted with the corresponding, but less complex aspects of Galvanometer Scanners (GSs). The issue of the non-linearity of the scanning functions of both PMs and GSs (and, consequently, of their variable scanning velocities) is approached, as well as characteristic angles, the angular and linear Field-of-View (FOV), and the duty cycle. A device with two supplemental mirrors is proposed and designed to increase the distance between the GS or PM and the scanned plane or lens to linearize the scanning function (and thus to achieve an approximately constant scanning velocity). These optical aspects are completed with Finite Element Analyses (FEA) of fast rotational PMs, to assess their structural integrity issues. The study is concluded with an optomechanical design scheme of PM-based scanning heads, which unites optical and mechanical aspects--to allow for a more comprehensive approach of possible issues of such scanners. Such a scheme can be applied to other types of optomechanical scanners, with mirrors or refractive elements, as well. laser scanners; Polygon Mirrors (PMs); Galvanometer Scanners (GSs); scanning function; scanning velocity; Field-of-View (FOV); multi-parameter analysis; Finite Element Analysis (FEA); optomechanical design +
Footnote †: journal: Applied Sciences  
13 OM Optomechatronics Group, Faculty of Engineering, \"[PERSON]\" University of Arad, Str. [PERSON] No. 2, 310177 Arad, Romania 12 Doctoral School, Polytechnic University of Timisoara, 1 Mihai Viteazu Avenue, 300222 Timisoara, Romania 2  
Footnote †: journal: Applied Sciences
a lower scanning resolution [1,2], and this makes them less attractive, especially for high-end applications such as biomedical imaging--including Optical Coherence Tomography (OCT) [43, 44, 45, 46, 47, 48, 49] and Confocal Microscopy (CM) [50]. Each system in the first category (i.e., of optomechanical scanners) has different advantages and drawbacks that makes it more suitable for a certain application. Broadly, in the competition between scanners with reflective and refractive elements, the former usually win, because of a higher versatility in terms of spectral range, as well as fewer aberration and dispersion issues. An exception could be made by Risley prisms scanners, because of their high positioning precision and velocity for two-dimensional (2D) scanning [37, 38, 39, 40, 41, 42], but in general, mirror-based systems (i.e., GSs and PMs) are the most common for the largest range of applications because of the above advantages [1, 2, 3, 4]. Within this latter narrower category, in the 1990s, the GSs seemed to take over the field almost completely because of their overall good characteristics, which include high positioning precision at a large Field-of-View (FOV) and good resolutions at satisfactory scanning velocities, all achieved in compact, light-weight constructions, and at a reasonable cost per scan axis. However, PMs seemed to make quite a comeback starting in the early 2000s because of their particular advantage: High scanning velocity. With the necessity to develop broadband laser sources scanned in frequency for Swept Source (SS) OCT [44], PMs caught the attention of both research [19, 20, 21, 22, 23, 24, 25, 26] and technological development [51].