Broadband THz to NIR up-converter for photon-type THz imaging

Abstract

High performance terahertz imaging devices have drawn wide attention due to their significant application in healthcare, security of food and medicine, and nondestructive inspection, as well as national security applications. Here we demonstrate a broadband terahertz photon-type up-conversion imaging device, operating around the liquid helium temperature, based on the gallium arsenide homojunction interfacial workfunction internal photoemission (HIWIP)-detector-LED up-converter and silicon CCD. Such an imaging device achieves broadband response in 4.2–20 THz and can absorb the normal incident light. The peak responsivity is 0.5 AW −1 . The light emitting diode leads to a 72.5% external quantum efficiency improvement compared with the one widely used in conventional up-conversion devices. A peak up-conversion efficiency of 1.14 × 10 −2 is realized and the optimal noise equivalent power is 29.1 pWHz −1/2 . The up-conversion imaging for a 1000 K blackbody pin-hole is demonstrated. This work provides a different imaging scheme in the terahertz band.

Optimization of the Cryogenic Light-Emitting Diodes for High-Performance Broadband Terahertz Upconversion Imaging

“…We find that the applied bias voltage drops mainly across the LED part, and then the additional bias voltage goes to the HIWIP part. This feature gives rise to a turn-on behavior of the HIWIP-LED device, which is in good agreement with the observed results in the previous experimental measurement [15]. The calculation results of the valence band diagram under different bias voltage are displayed in Figure 4B.…”

“…The difference between the experiment and the calculation is mainly caused by the internal photon recycling. A dramatic increase of the LEE could be realized by optimizing the photon recycling process [27,28], but at the same time the quality of the images will be significantly reduced [15]. In contrast, the most direct and effective method to improve the LEE is to change the shape of the semiconductor/air interface and include the use of roughened or textured semiconductor surfaces.…”

“…The detailed calculation of the NEP could be found in the Supplementary Materials and Refs. [15,32]. The bias voltage range start from the value of 1.4 V corresponds to the turn-on voltage of HIWIP-LED.…”

“…Therefore, this THz QWP-LED pixelless imaging device is far from an optimization for the thermal imaging. The upconversion device based on the homojunction interfacial workfunction internal photoemission (HIWIP) detector and LED allows normal incidence excitation and realizes a broadband (4-20 THz) THz to NIR upconversion [15]. However, the current limiting factor for this imaging scheme is the low upconversion efficiency.…”

“…In fact, the problem of low upconversion efficiency also plagues almost all III-V compound semiconductor based upconversion devices. The upconversion efficiency of the MIR or THz upconverter are all below the level of 0.01 W/W [15][16][17], which greatly restrains the efficiency and quality of the pixelless imaging. How to improve the upconversion efficiency is an urgent problem for HIWIP-LED pixelless imaging devices.…”