Designing a Spectrograph for Observation of Microparticles in the Ionosphere

Abstract: In this report the development of a spectrograph for confirming the size of the particles in a particle cloud is described. With the wavelength dependency of Mie-scattering, it can be determined if the particles are of the desired size. There is a significant trade-off effect between size and resolution of an optical system. The spherical aberrations that arise due to the focal length being short compared to the lens diameter are reduced by using lens combinations called achromatic doublets, both as collimating and focusing lenses. The manufactured spectrograph has a resolution of about 10 nm that is approximately as expected from the optical design. But the spectrograph suffers from stray light. This remains to be reduced with aperture stops, non-reflective interior and fore-optics.