Terahertz electrometry via infrared spectroscopy of atomic vapor

Here a system of electrometry in which a THz signal can be characterized is demonstrated using laser spectroscopy of highly excited (Rydberg) atomic states. The proof-of-principle measurements here reveal a minimum detectable THz electric field amplitude of $1.07 \pm 0.06 \mathrm{~V} / \mathrm{m}$ at 1.06THz with $3 \mathrm{~ms}$ detection time, corresponding to a THz power at the atomic cell of approximately 3.4nW. This method is applicable across the THz and millimeter-wave range. The relative simplicity and cryogen-free nature of this system makes it potential to provide a route to a SI traceable THz calibration technique and provide an alternative to calorimetric methods.