MEMS Varifocal Mirror for High-Power Laser Focusing

Today, lasers are used in many surgical procedures due to their ability of performing precise incisions, and ablations. With the development of fiber-coupled lasers, even minimally invasive procedures started making use of laser tools. However, existing fiber tools do not provide the same performance as traditional laser systems, often causing significantly more tissue carbonization. This can be attributed to the lack of optics in fiber tools, which requires the tip of the fiber to be placed in direct contact with the tissue, increasing the collateral damage of the laser. To avoid this issue, a compact focusing system should be integrated in the fiber tool. However, traditional optical systems based on moving lenses are too large and bulky for that. To solve this problem, this thesis proposes a focusing system based on MEMS deformable mirrors. Using microfabrication methods, we develop a novel MEMS varifocal mirror, designed for focusing high-power laser in a fiber laser system. The design of this mirror is based on state-of-the-art MEMS deformable mirrors, which have been proposed for microscopy applications, with significant adaptations for high-power lasers, including different actuation mechanisms and control strategies. We explore the use of hydraulic actuation to achieve large focal length range, while providing compatibility with high-power laser. The deflection of the mirror is controlled using a feed-forward model, in which parameters are obtained through characterization of the fabrication process. This allows controlling the mirror without a beam splitter or external sensors, which contributes to the miniaturization of the focusing system.