A terahertz spectrometer for the study of multilayered optics & complex materials
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Date
2021
Authors
Ahmed, Akif
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Abstract
Time domain spectroscopy with terahertz (THz) pulses is a powerful technique in characterizing material properties. THz technology is still developing and many optical components in this electromagnetic spectrum are not yet so economically available. We construct a THz spectrometer utilizing ultrashort laser pulses in nonlinear crystals that allows phase-resolved detection of light in the bandwidth 0.25-2.25 THz. Using our instrument, we examine spectral features of ordinary low loss materials which are later exploited in the study of multilayered dielectric structures designed to serve as low-cost optics for THz light. We develop wideband antireflection (AR) coatings for a variety of substrates with commercially available films and tapes. Utilizing multilayered structures, we propose the design of an economic, yet efficient, THz linear polarizer. In addition, we designed and constructed distributed Bragg reflectors which are incorporated in building a tunable Fabry-Perot cavity. With the aid of an AR coated electro-optic crystal, high resolution time domain spectroscopy performed on room temperature magnetoelectric multiferroic, BiFeO3 (BFO), showed the presence of electromagnon resonances in the sub-THz range. BFO is a potential material for the study of strong light matter coupling, which can have a substantial technological impact. We have tried tuning the resonances of BFO with applied electric field and optical heating in order to observe polariton modes. Due to the challenges in tuning BFO magnons, we investigate the design aspects of a high Q cavity for the discovery of a hybrid quasiparticle at room temperature, cavity magnon polariton (CMP), in the promising multiferroic. We have performed calculations showing both frequency and time domain response of the empty cavity system to highlight experimental implications for our apparatus. The tools developed in this thesis will be used in the study of CMP in BFO in a future project alongside other research.
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Keywords
Terahertz, THz-TDS, Antireflection coating, DBR, Polarizer, Bismuth Orthoferrite, BiFeO3, Cavity Polariton