High-Resolution, Low-Noise Imaging in THz Polaritonics

Time-resolved imaging of propagating electromagnetic waves at terahertz (THz) frequencies provides deep insights into waves and their interaction with a variety of photonic elements. As new components for THz control are developed, such as metamaterial microstructures that display deep sub-wavelength E-field localization, finer spatial resolution and more sensitive imaging techniques are required to study them. Here we introduce key advances in the optical design and lock-in image acquisition at 500 Hz for the complementary imaging techniques of phase contrast and polarization gating. Compared to other methods, this leads to a 4-fold improvement in resolution and up to 5-fold reduction in noise through suppression of low frequency laser fluctuations. With a resolution better than 1.5 μm (λ/100 at 0.5 THz) and a noise floor of 0.2%, phase contrast imaging presents new opportunities for studying very fine structures and near-fields in the THz regime. For most other experiments, polarization gating imaging is preferred because its noise floor is lower at 0.12% and its <; 5 μm resolution is typically more than sufficient.