Hochschulschrift:
Dissertation, Universität Freiburg, 2021
Anmerkungen:
Research in micro-optics. - [Freiburg]
Beschreibung:
Abstract: Mid-infrared (MIR) spectroscopy is a powerful technique to detect different chemical species. With the rapid development of the microreactors, online spectral monitoring systems are required for real-time chemical analysis. Approaches based on Fourier-transform infrared (FTIR) spectroscopy has been developed recently. However, these systems are bulky and expensive. Therefore, novel approaches for miniaturized and cost-effective online monitoring systems are investigated in this work, focusing on the development of Fabry-Perot (FP) filters, which are the essential wavelength-selective components. <br><br>In this thesis, three types of FP filters based on Bragg mirrors are demonstrated: two static FP filters, emphasizing stable and fast detecting systems; and a tunable FP filter, addressing a novel actuation mechanism.<br>The four-step filter with four different transmission peaks in the MIR range was designed and fabricated with Micro-Electro-Mechanical-Systems (MEMS) technology. The thin-membrane filter shows high spectral resolution with the best full-width at half-maximum (FWHM) of 19 nm.<br><br>The two-step static filters were implemented as an array to realize the spatial resolution with a pixel size of 2×2 mm2. A well-controlled MEMS fabrication process was developed, allowing the precise definition of transmission wavelengths of the filters in order to match the absorption peaks of the chemicals. Experimental results proved that the designed system was able to monitor the photochemical reaction and to identify different solution concentrations.<br><br>The tunable FP filter was actuated by novel actuators made of liquid crystal elastomers (LCEs). The LCE layers worked as spacers between the Bragg mirrors to change the filter cavity thickness. The MEMS-fabricated filter has a FWHM of 143 nm at 4.58 μm. A tuning range of the filter of 260 nm was realized with the maximum applied voltage of 7.3 V (0.5 W) for each actuator