Processing of transparent oxide ceramic materials for infrared sensor applications

Transparent ceramic materials offer superior mechanical, optical and chemical properties compared to common transparent materials such as glasses and polymers. Their extended transmission window up to the near infrared wavelength range makes the ceramics suitable for application in optical devices such as laser components, optical lenses and sensor systems. However, the fabrication of transparent ceramics is challenging. To provide optical transparency, pores and impurity phases must be avoided, i.e., very pure raw materials must be used and the ceramic processing chain including shaping, thermal processes and hard machining must be conducted very thoroughly. Finally, residual porosity must be avoided. In this work, the impact of the processing on microstructural and therefore optical properties of the ceramic materials MgAl2O4, Y2O3 and MgO are investigated. The wide transmission window of these ceramics, in combination with their mechanical stability, makes them suitable for the usage in sensors of infrared radiation, i.e., for the detection of IR-active gaseous or organic molecules. For this application, a very high spectral infrared transmission must be achieved, which is only possible by establishing a reliable processing for all materials. The main goal of this work is the production of monolithic ceramic windows with high relative density and therefore suitable transmission for optical sensor applications. Challenges and modifications along the processing chain are investigated with respect to their impact on the functional properties of the transparent ceramic windows. Furthermore, the relationship between processing, microstructure and optical properties will be emphasized.