Development of novel compact ultrashort pulse lasers for biomedical applications

Abstract

Lasers have established their ubiquity across a broad spectrum of applications, ranging from manufacturing and communication to entertainment, and the medical field is no exception. However, biomedical applications place unique demands on laser parameters such as operating mode, wavelength, and output power. Furthermore, the physical characteristics of the laser must include reliable operating stability, high resistance to fluctuations of environmental conditions, and compact size. The requirements for these laser parameters strongly depend on the specific application, as different laser modes, irradiation levels, and exposure durations cause diverse effects on various tissue types. Therefore, a comprehensive understanding of light-tissue interaction with the target tissues is essential before designing lasers for biomedical purposes. This thesis provides experimental and computational research, shedding light on the interaction of post-mortem mouse head tissues with continuous-wave light and ultrashort pulses. The study reveals the tissue penetration depth of single- and multi-layers of skin, skull, and brain in visible and near-infrared ranges, providing valuable information about their optical properties and required laser parameters for non- or minimal invasive neurostimulation. The dissertation is devoted to the improvement of neurostimulation methods, including a comprehensive study of the optical properties of light-sensitive proteins applicable as optogenetic tools and fluorescent biomarkers and the development of a compact ultrashort-pulse high-peak-power laser system for optogenetic research on in vivo animal samples. In addition, the work presents a developed tunable fibre laser operating at wavelengths of 850 nm and 1700 nm that can be used as a versatile light source in the multimodal cancer detection system. The work presented in the dissertation includes the development of different laser sources intended for applications in biomedical research, neurophotonics, and tumour diagnostics.