Abstract
We demonstrate for the first time the ability to perform time resolved imaging of terahertz (THz) waves propagating within a photonic crystal (PhC) slab. For photonic lattices with different orientations and symmetries, we used the electro-optic effect to record the full spatiotemporal evolution of THz fields across a broad spectral range spanning the photonic band gap. In addition to revealing real-space behavior, the data let us directly map the band diagrams of the PhCs. The data, which are in good agreement with theoretical calculations, display a rich set of effects including photonic band gaps, eigenmodes and leaky modes.
Highlights
IntroductionIt is possible to characterize the interactions of the THz fields with these elements via time-resolved, phase-sensitive imaging [8] and to display the images from separate measurements in ‘movie’ form that shows wave propagation at lightlike speeds through the material
We studied THz-frequency photonic crystal (PhC) slab structures in classic geometries that have been embedded in a LiTaO3 host, which is relatively isotropic compared to LiNbO3 (|εeo − εo| ≈ 4 for LiTaO3 compared to 15 for LiNbO3 [1])
The THz waves were generated in a non-machined portion of the slab and propagated toward a square array of air holes machined into the LiTaO3 host with a lattice constant of 100 μm (see figure 1(b))
Summary
It is possible to characterize the interactions of the THz fields with these elements via time-resolved, phase-sensitive imaging [8] and to display the images from separate measurements in ‘movie’ form that shows wave propagation at lightlike speeds through the material During this same time period, photonic crystals (PhCs) have emerged as versatile tools for controlling radiation across the electromagnetic spectrum [9]. While our present work focuses on well-known PhC geometries and behaviors, our ability to image and characterize the near-fields within PhCs is only possible because of recently developed imaging and machining capabilities These can be used in the future to observe more interesting wave phenomena (e.g. negative refraction). As new theoretical ideas for PhC devices are developed, direct visualization of the E-fields will be a valuable tool for testing and verification
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