Biomedical subjects
Publications and source records attributed to David W Ward.
Using femtosecond laser machining, we fabricated a terahertz resonant cavity in LiNbO3. Optical pulse sequences with variable repetition rates, generated through a novel pulse-shaping method, are used for characterization of the cavity resonances and for amplification of terahertz phonon-polaritons in the cavity.
We report the generation of aberration-free cylindrical phonon-polariton wave packets in uniaxial LiTaO3 crystals by nonresonant impulsive stimulated Raman scattering. The unique properties of phonon polaritons with a typical carrier frequency in the THz regime allow direct measurement of the spatiotemporal amplitude and phase distributions. We demonstrate that under these conditions the phase anomaly (Gouy phase) may be visualized directly through spatiotemporal imaging as the cylindrical wave propagates through its focus.
Generation and control of pulsed terahertz-frequency radiation have received extensive attention, with applications in terahertz spectroscopy, imaging and ultrahigh-bandwidth electro-optic signal processing. Terahertz 'polaritonics', in which terahertz lattice waves called phonon-polaritons are generated, manipulated and visualized with femtosecond optical pulses, offers prospects for an integrated solid-state platform for terahertz signal generation and guidance. Here, we extend terahertz polaritonics methods to patterned structures. We demonstrate femtosecond laser fabrication of polaritonic waveguide structures in lithium tantalate and lithium niobate crystals, and illustrate polariton focusing into, and propagation within, the fabricated waveguide structures. We also demonstrate a 90 degrees turn within a structure consisting of two waveguides and a reflecting face, as well as a structure consisting of splitting and recombining elements that can be used as a terahertz Mach-Zehnder interferometer. The structures permit integrated terahertz signal generation, propagation through waveguide-based devices, and readout within a single solid-state platform.