Terahertz Imaging with a Quantum Cascade Laser and a Pixelless Imaging Chip

Abstract

Terahertz imaging has drawn a widely attention for the potential applications in deep space exploration, material analysis, medical imaging, security screening, and situation awareness in fire disasters nowadays <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1–5</sup> . However, lack of large-format (many-pixels) sensor arrays, especially the fast imaging arrays, is one of the major hurdles for the proliferation of THz sensing methodologies and related applications <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> . Therefore, we fabricated a pixel-less photo-type terahertz imager based on the frequency up-conversion technique to realize the real-time and fast THz imaging. The device is composed of a terahertz quantum well photodetector (THz QWP) and a near-infrared light emitting diode (LED) that grown in sequence on the same substrate with molecular beam epitaxy. In such an integrated device (THz QWP-LED), electronics of the THz QWP in the bound state were excited to the continuous state to form photocurrent by absorbing of THz photonics, and it drives the LED to emit near-infrared light. The chip has a peak response of ∼0.5 A/W at 4.8 THz and a noise equivalent power (NEP) of ∼ pW/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sup> . We setup terahertz imaging systems to base on a quantum cascade laser (QCL) and a THz QWP-LED. The systems has an imaging resolution of ∼ <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$100\ \mu\ \mathrm{m}$</tex> and a capacity of fast imaging within 10 µs. This device opens a new way to realize high performance real-time and fast terahertz imaging.