Study of spectral sensing using electro-optic films

Kashma K. Rai

doi:10.17918/etd-3274

Fundamental studies on light interacting with liquid crystals (LCs) and polymers have led to innovative application like the omnipresent LCDs, revolutionizing the display industry. This thesis focuses on manipulation of optical propagation through LC/polymer two phase composite material set and in-depth understanding of these systems by studying their morphology and microscopic interactions for multiwavelength sensing applications. Holographically formed Polymer Dispersed Liquid Crystals (HPDLCs) are the composite photorefractive material used in this work. They consist of LC nanodroplets confined in a polymer matrix, arranged in periodic planes. Applying an electric field across them modifies their periodic refractive index to a uniform refractive index state, due to LC realignment. This transforms the reflective HPDLCs into an optically transparent state. Fabricating and assembling HPDLCs in different configurations enables wavelength filtering by controlling their optical lineshape output, for wavelength sensing applications. To increase the range of wavelengths spanned, these electro-optic thin films are arranged in serial and parallel design. A novel dynamic time multiplexing technique is used to improve the spectral range of individual HPDLC unit. These types of field controllable HPDLC wavelength filtering devices have remote sensing, imaging spectrometry applications like hyperspectral and multispectral imaging to detect specific spectral signature of an unknown remote object source. Comparing the detected spectra to a database of known spectral fingerprints enables identification of the unknown entity. To further fundamentally comprehend the LC polymer interaction in HPDLC systems structural analysis data using microscopy and spectroscopy techniques is presented. To interpret the nano-scale structure accurately and better understand the confined LC behavior, variable pressure scanning electron microscopy and electron spin resonance spectroscopy is used here for the first time. Berreman 4 4 matrix technique and a phenomenological diffusion model are presented to model and predict their optical output behavior and their multipart wavelength lineshapes. In summary this dissertation focuses on study of multi spectral sensing using HPDLCs, their fundamental studies along with modeling their behavior.

Study of spectral sensing using electro-optic films

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Study of spectral sensing using electro-optic films

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