Full-Field, Room-Temperature Terahertz Imaging at Kilohertz Frame Rates using Atomic Vapour

THz imaging systems are in demand across a range of diverse applications such as biomedical imaging, security scanning, and non-destructive testing [1]. This is due to the non-ionising and penetrating nature of THz radiation. However, a system capable of fast and sensitive full-field imaging remains an unfulfilled goal [2]. Here we report on the demonstration of a 2D THz imaging system capable of fast and low noise full-field imaging. At the heart of the technique is efficient THz-to-optical conversion within an atomic vapour close to room temperature. Infra-red pump lasers excite Cs atoms within a 50 μm × 1 cm × 1 cm region of a vapour cell to an excited Rydberg state. An incident THz field transfers these Rydberg atoms to a nearby electronic state that decays rapidly via an optical fluorescence channel. The atoms thereby act as an atomic THz sensor that fluoresces optically in response to THz radiation [3]. This optical response to THz radiation enables us to capture THz images using standard CCD detector technology thus avoiding the need for cryogenic cooling required by other sensitive techniques. Using illumination from a low-power (<; 10 μW) THz source, we detect full-field images of 250 × 250 pixels, with capture rates of >3 kHz, and measure a mimimum detectable power of 8 fW/px/s
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. Figure 1 shows frames from high speed video images of (a) a chopper wheel taken at 3 kHz and (b) a falling water droplet taken at 500 Hz. This novel method for THz imaging is orders of magnitude faster and more sensitive than other room-temperature techniques and allows imaging of dynamic processes not possible by any other method.