Ultra-compact holographic spectrometers for diffuse source spectroscopy
MetadataShow full item record
Compact and sensitive spectrometers are of high utility in biological and environmental sensing applications. Over the past half century, enormous research resources are dedicated in making the spectrometers more compact and sensitive. However, since all works are based on the same structure of the conventional spectrometers, the improvement on the performance is limited. Therefore, this ancient research filed still deserves further investigation, and a revolutionary idea is required to take the spectrometers to a whole new level. The research work presented in this thesis focuses on developing a new class of spectrometers that work based on diffractive properties of volume holograms. The hologram in these spectrometers acts as a spectral diversity filter, which maps different input wavelengths into different locations in the output plane. The experimental results show that properly designed volume holograms have excellent capability for separating different wavelength channels of a collimated incident beam. By adding a Fourier transforming lens behind the hologram, a slitless Fourier-transform volume holographic spectrometer is demonstrated, and it works well under diffuse light without using any spatial filter (i.e., slit) in the input. By further design of the hologram, a very compact slitless and lensless spectrometer is implemented for diffuse source spectroscopy by using only a volume hologram and a CCD camera. More sophisticated output patterns are also demonstrated using specially designed holograms to improve the performance of the holographic spectrometers. Finally, the performance of the holographic spectrometers is evaluated and the building of the holographic spectrometer prototype is also discussed.