The orbital angular momentum (OAM) of photons is a promising degree of freedom for high-dimensional quantum key distribution (QKD). Due to the greater flexibility in applications and the lower loss, QAM QKD over the free-space channel is still significant. However, effectively mitigating the adverse effects of atmospheric turbulence is a persistent challenge. In contrast to previous works focusing on correcting static simulated turbulence, we investigate the performance of OAM QKD in real atmospheric turbulence with real-time adaptive optics (AO) correction. We show that, it is possible to mitigate the errors induced by weak turbulence and establish a secure channel under some conditions. The cross-talk induced by turbulence and the performance of AO systems are investigated in a lab-scale link with controllable turbulence. The relations between the crosstalk and AO specifications is also studied. Our experimental results suggest that an advanced AO system with fine beam tracking, reliable beam stabilization, precise wavefront sensing and accurate wavefront correction is necessary to adequately correct turbulence-induced error.
Computational sampling methods have been implemented to spatially characterize terahertz (THz) fields. Previous methods usually rely on either specialized THz devices such as THz spatial light modulators, or complicated systems requiring assistance from photon-excited free-carriers with high-speed synchronization among multiple optical beams. Here, by spatially encoding an 800 nm near-infrared (NIR) probe beam through the use of an optical SLM, we demonstrate a simple sampling approach that can probe THz fields with a single-pixel camera. This design does not require any dedicated THz devices, semiconductors or nanofilms to modulate THz fields. By using computational algorithms, we successfully measure 128×128 field distributions with a 62 μm transverse spatial resolution, more than 15 times smaller than the central wavelength of the THz signal (940 μm. Benefiting from the non-invasive nature of THz radiation and sub-wavelength resolution of our system, this simple approach can be used in applications such as biomedical sensing, inspection of flaws in industrial products, and so on.
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