Exploiting second-order nonlinear phenomena for the generation and detection of coherent terahertz electric fields

• Author / Creator

  Carnio, Brett N

• This thesis explores terahertz radiation sources and detectors, where the driving physical mechanism for generation and detection is second-order nonlinear phenomena. The heart of this work considers novel crystals and waveguiding arrangements for terahertz radiation generation and/or detection to advance the field of nonlinear optics.

  Experimental investigations are conducted using emerging pnictide and chalcogenide ternary crystals for both the generation and detection of terahertz radiation. While a CdSiP2 crystal is shown to provide appreciable optical rectification phase-matching (surpassing that of a ZnGeP2 crystal), an AgGaSe2 crystal exhibits unprecedented optical rectification phase-matching (coherence length of ~800 µm for frequencies between 0.5-2.9 THz). A BaGa4Se7 crystal is revealed as a highly-efficient terahertz radiation emitter (i.e. the terahertz radiation power produced by BaGa4Se7 is better than ZnTe in select terahertz spectral bands). Subsequently, a ZnGeP2 crystal is shown to exhibit exceptional electro-optic phase-matching, allowing it to surpass the bandwidth of ZnTe for terahertz radiation detection.

  Numerical and experimental techniques are utilized to investigate waveguiding arrangements for terahertz radiation generation. However, due to the lack of numerical methods capable of incorporating all 18 dispersive second-order nonlinear tensor elements, two separate formalisms are developed to integrate second-order nonlinear effects into finite-difference time-domain simulations. Using the developed methods and experimental terahertz time-domains spectroscopy techniques, LiNbO3 planar waveguides are investigated for producing terahertz radiation. Key observations include ultra-broadband terahertz radiation generation spanning 0.18-106 THz, terahertz radiation generation enhancement near the phonon resonances of LiNbO3, phase-matched terahertz radiation produced in the backward direction (i.e. the direction opposite to the propagation direction of the excitation electric field), and high experimentally-realized optical-to-terahertz conversion efficiencies (i.e. >10-5).

  Interestingly, the aforementioned nonlinear finite-difference time-domain formalisms are not restricted to the terahertz frequency regime, but can accurately model second-order nonlinear processes within various other spectral regions. To make use of such an exciting outcome, this thesis briefly extends beyond the terahertz spectral regime to examine second-order nonlinear effects for the generation of radiation in the infrared and visible spectral regimes. Accordingly, an entirely new class of multi-band photonic sources is proposed, in which a single waveguiding structure concurrently satisfies phase-matching for several second-order nonlinear processes. A multi-band waveguide is experimentally-realized, which simultaneously produces phase-matched THz radiation and phase-matched radiation in the visible spectral regime.

  The findings in this thesis are invaluable to the continuing development of terahertz radiation sources and detectors being driven by the physical mechanism of second-order nonlinear phenomena.

• Subjects / Keywords

  • Terahertz
  • Nonlinear optics

• Graduation date

  Spring 2022

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-yzx4-5g13

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.