Understanding of terahertz spectroscopic properties of materials is crucially important for applications of terahertz waves in sensing. Spectroscopic properties of water-rich media, such as biological tissues, gels, and aqueous solutions, are strongly affected by the amount and the dynamics of water in them. Terahertz spectroscopical measurements can clarify the dynamical and/or structural characteristics of water molecules in the hydrogen-bond network in these media. We studied the dynamical properties of water around protein molecules and polymers in aqueous solutions using terahertz spectroscopic measurements. Sensing of liquid using a terahertz waveguide composed of a metal rod array will also be described.
We have observed coherent synthesis of spatial profiles of THz radiation emitted from a photoconductive antenna array.
The antenna array is composed of seven independently addressable photoconductive antenna units having interdigitated
electrodes. The antennas were pumped by amplified 800 nm femtosecond optical pulses. Emitted THz radiation was
focused, and the time-resolved spatial profile of the THz radiation on the focal plane was observed using a newly developed
real-time imaging apparatus, which can correct the terahertz field images for nonuniformity in birefringence of the EO
crystal. By scanning the delay time, frequency-resolved images were also obtained, which exhibit frequency-dependent
field profiles. Field profiles observed were coherent superpositions of terahertz waves emitted from the antenna units
constituting the array. By inverting the bias voltage to the central unit of the emitter array, we observed super-resolution
beam size of terahertz waves, which are smaller than the diffraction limit.
Terahertz electromagnetic pulse generation using photoconductive emitters, their characterization, real-time imaging, and spectroscopies using them are described. Intense THz pulses were generated using a large-aperture photoconductive antenna. Real-time imaging were performed for the pulse characterization and acquisition of 1-kHz high-speed movies of moving objects. Tunable THz pulse generation and ultrafast semiconductor spectroscopy using photoconductive antennas will also be described.
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