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Développement de microlasers polymériques à modes de galerie à base de nanocristaux de semi-conducteurs

Year: 2024
Type: dissertation
Abstract: Interest in whispering gallery mode microcavities has been growing over the past two decades. Circular microcavities exhibit confined optical modes due to total internal reflection associated with their high refractive index, which are resonant at specific wavelengths. These so-called gallery modes exhibit a strong evanescent electromagnetic field at the interface with the external medium, extending up to several tens of nanometers from the surface. The wavelength of these resonances is thus extremely sensitive to experimental conditions (cavity size, temperature, refractive index of the external medium, or even its chemical composition).These optical properties make them excellent tools for various applications. Firstly, for photonic applications, whispering gallery modes microcavities can serve as light sources integrated into photonic circuits as well as frequency optical filters thanks to their extremely fine resonances. Secondly, these microcavities can serve as highly precise detection systems. This can range from detecting the presence of gas in a room, a variation in temperature, to ultra-sensitive detection of molecules of interest in a solution. The detection mode uses either the detection of the spectral shift of the resonances or the interaction of the cavities' evanescent field with molecules of interest. Lastly, whispering gallery modes microcavities can serve as microlasers, extremely useful for both detection applications and photonics applications. Their small dimensions combined with high quality factors make them one of the best alternatives for laser miniaturization. Currently, the fabrication of these whispering gallery modes microlasers relies on expensive materials and manufacturing methods, or does not allow for the production of a large number of robust and stable cavities over time.During my thesis, I developed a fabrication process for polymeric microcavities in the form of microdisks based on laser photolithography. This process allows for the fabrication of a large number of microdisks using a durable and low-cost material, spatially organized in a controlled manner on a substrate. These microdisks have a quality factor of at least 6000, a result similar to the best quality factors found in the literature for polymeric cavities. I synthesized semiconductor nanocrystals to use as an integrated light source in these microdisks. I developed a chemical process to specifically attach these nanocrystals to the surface of the microdisks, then observed the coupling of the nanocrystals' emission to their gallery modes. I then conducted a comparative study on the optical gain properties of different types of semiconductor nanocrystals (core-shell structures, quantum shells, and nanoplatelets) in solution to determine the best candidates to integrate into the microcavities for achieving a laser effect. Finally, I integrated the best emitters into the microdisks and characterized the laser effect in these microcavities. I compared the laser thresholds obtained for different materials under various experimental conditions, eventually observing laser thresholds at pump powers below 100 µJ/cm². I proposed a new spectroscopic model to explain the single-exciton laser effect in these nanocrystal microlasers. These microlasers, obtained through a simple fabrication process, are promising and could serve as a basis for numerous applications, both in detection and in photonic circuits.
Language: English
Open Access status: green
OpenAlex ID: W7065143718
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