The doctoral dissertation in the field of Physics will be examined at the Faculty of Science, Forestry and Technology, Joensuu campus.
What is the topic of your doctoral research? Why is it important to study the topic?
My doctoral research focuses on the fabrication of dielectric grating mirrors for laser applications. These nanostructured mirrors are designed to control the spectral and polarization properties of laser beams directly within the cavity, enabling compact, efficient, and high-performance laser systems.
The importance of this topic lies in the demand for miniaturized, high-performance lasers for applications in photonics, sensing, and manufacturing. Traditional laser designs often require multiple bulky components to achieve beam shaping and polarization control. By integrating grating mirrors into the cavity, we simplify the laser designs while achieving the desired functions.
Moreover, dielectric gratings offer high damage resistance and diffraction efficiency, making them suitable for high-power lasers. This research contributes to the development of more robust and efficient lasers.
What are the key findings or observations of your doctoral research?
High-precision fabrication processes for dielectric grating mirrors are developed in this doctoral research. These mirrors were implemented in two laser systems: a microchip laser achieving single-mode emission, and a thin-disk laser generating radially polarized beams. Reactive ion etching was adapted for thick substrates to improve the thermal stability of laser performance. Etching processes were developed for tantalum pentoxide, niobium pentoxide, and hafnium dioxide, which are of interest due to their high refractive index and laser damage resistance. The research also introduces methods to quantify pattern distortion in nanoimprint lithography, contributing to more accurate patterning.
These innovations are valuable for both scientific research and industrial applications, offering fabrication processes that can be transferred to other nanostructures besides gratings and which can benefit many photonic applications besides lasers.
What are the key research methods and materials used in your doctoral research?
The research primarily focuses on the fabrication of grating mirrors using lithographic techniques, while touching briefly on grating design using the Fourier modal method and experimental validation in laser setups. These mirrors are made from all-dielectric materials.
The fabrication process involves thin-film deposition, lithographic patterning, and reactive ion etching. The etching processes were developed through experimental trials. Surface characterization was performed using scanning electron microscopy, ellipsometry, and spectrophotometry to verify pattern dimensions and optical performance.
The laser performance of these grating mirrors was validated in a microchip laser setup and a thin-disk laser setup. The research also included distortion analysis in nanoimprint lithography using overlay patterning with optical lithography.
The doctoral dissertation of Fangfang Li, MSc, entitled Fabrication of dielectric grating mirrors for lasers will be examined at the Faculty of Science, Forestry and Technology, Joensuu campus. The opponent will be Dr. Alke Meents, Deutsche Elektronen Synchrotron DESY, and the custos will be Professor Markku Kuittinen, University of Eastern Finland. Language of the public defence is English.
For more information, please contact:
Fangfang Li, [email protected]
