Visualization of the spatial–temporal evolution of continuous electromagnetic waves in the terahertz range based on photonics technology

Abstract

Visualization of the field evolution of the continuous waves in the terahertz (THz) range with high phase and spatial resolution is a new approach to the study of the physical dynamics of unique beams, such as nondiffractive, self-reconstructing, and vortex beams. As near-field visualization can reveal device dynamics, it is also useful for diagnosing the THz devices. Here, we demonstrate the visualization of the spatial–temporal evolution of freely propagating continuous THz waves by adapting the nonpolarimetric electro-optic (EO) detection technique to the self-heterodyne system. The amplitude and phase of a THz wave (125 GHz, λ=2.4 mm, 650 μW) radiated from a horn antenna were simultaneously and precisely measured in the self-heterodyne system, in which two frequency-detuned free-running lasers were used both for the generation (photomixing) and EO detection of THz waves. The nonpolarimetric EO detection technique has solved an intrinsic problem of the conventional polarimetric EO detection technique, in which the sensitivity of the measurements can be changed drastically by the fluctuation of the polarization state of the optical local oscillator signal for the EO detection. As a result, field evolution could be visualized with a maximum signal-to-noise ratio of 27 dB and a phase resolution of 2π/78 rad (80 mrad), by scanning an optical fiber-mounted EO crystal (ZnTe) in a free space repeatedly.