Continuous wave terahertz detection using 1550 nm pumped nonlinear photoconductive GaAs metasurfaces.

Terahertz (THz) continuous wave (CW) spectroscopy systems can offer extremely high spectral resolution over the THz band by photo-mixing high-performance telecommunications-band (1530-1565 nm) lasers. However, typical THz CW detectors in these systems use narrow band-gap photoconductors, which require elaborate material growth and generate relatively large detector noise. Here we demonstrate that two-step photon absorption in a nano-structured low-temperature grown GaAs (LT-GaAs) metasurface which enables switching of photoconductivity within approximately one picosecond. We show that LT-GaAs can be used as an ultrafast photoconductor in CW THz detectors despite having a bandgap twice as large as the telecommunications laser photon energy. The metasurface design harnesses Mie modes in LT GaAs resonators, whereas metallic electrodes of THz detectors can be designed to support an additional photonic mode, which further increases photoconductivity at a desired wavelength.

太赫兹（THz）连续波（CW）光谱系统通过对高性能电信波段（1530 - 1565 nm）的激光进行光混频，能够在太赫兹频段提供极高的光谱分辨率。然而，这些系统中典型的太赫兹连续波探测器使用窄带隙光电导体，这需要精细的材料生长过程，并且会产生相对较大的探测器噪声。在此，我们证明了在纳米结构的低温生长砷化镓（LT - GaAs）超表面中发生的两步光子吸收，能够在约1皮秒内实现光电导率的切换。我们表明，尽管LT - GaAs的带隙是电信激光光子能量的两倍，但它仍可在连续波太赫兹探测器中用作超快光电导体。该超表面设计利用了LT - GaAs谐振器中的米氏模式，而太赫兹探测器的金属电极可被设计为支持一种额外的光子模式，这进一步提高了在所需波长处的光电导率。