Polymer dye lasers

Formålet med dette Ph.D. arbejde har været at udvikle miniaturiserede polymer farvestoflasere, egnet til at blive integreret i mikrochips som også indeholder andre polymerstrukturer – som for eksempel kan findes i ”Laboratorie-på-en-chip” kredsløb. Lasernes funktion skal være at levere lys til meget følsomme sensorformål, og at undgå at skulle opliniere eksterne lyskilder til sensorer på polymerchips. En enkelt type gennemsigtig ”resist” (SU-8) er blevet brugt til at udvikle en række laserresonatorer i polymer. ”Resisten” er blevet formgivet via en række lithografiske teknikker: UV lithografi, elektronstrålelithografi og Röntgenstrålelithografi. Andre polymerer er også blevet formgivet via ”nanoimprint” lithografi for at skabe laserresonatorer. En række lasere, både baseret på et flydende forstærkningsmedium og et faststof forstærkningsrmedium er blevet udviklet. Laserne giver både lys i flere ”modes” og i een enkelt optisk ”mode”. Laserne er baseret på en mængde forskellige optiske egenskaber af polymer tyndfilm og vædsker. De praktiske muligheder for at integrere polymer farvestoflaserne demonstreres ved at integrere en mængde optiske og væske- komponenter på en enkelt chip sammen med en miniaturiseret farvestoflaser. The purpose of this project has been to develop miniaturized polymer dye lasers that can be integrated on microchips containing other polymer ”laboratory on a chip” circuitry. The envisioned function of the polymer dye lasers has been to deliver light for sensing purposes, either for wavelength dependent absorption or for interference based sensing, for example with integrated Mach-Zehnder interferometers.In order to develop this kind of lasers, the project has focused on using a single transparent type of resist (SU-8) that can be patterned via several methods. The methods that have been tried on this resist are UV lithography, electron beam lithography and X-ray lithography. Apart from SU-8, a few alternative polymer types have also been used for forming laser structures via nanoimprint lithography.Throughout the work, several laser resonator types have been fabricated in polymer materials. The resonators range from simple parallel mirror types to first order Bragg grating distributed feedback resonators. Through the optical characterization of the laser type range, the possibilities for forming such miniaturized polymer dye lasers are revealed.Some techniques for modelling micro-optical structures are presented as a suggestion of how to predict the behavior of miniaturized polymer dye lasers and micro-optical structures in general.Both lasers operating in multi-mode and single polarization lasers operating on pre-determined single mode wavelengths are demonstrated. The mode structure of the lasers are controlled by the design of the laser resonators. Integration of a miniaturized polymer dye laser is demonstrated in two examples where the laser delivers light to an absorption cell, which makes it possible to measure the wavelength selective absorption of the fluid in the cell.The findings presented in the thesis forms a basis for selection of laser design for new applications both with respect to integration and to further development of polymer dye laser light sources.