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Frequency Up-Conversion Photon-Type Terahertz Imager.

ABSTRACT: Terahertz imaging has many important potential applications. Due to the failure of Si readout integrated circuits (ROICs) and the thermal mismatch between the photo-detector arrays and the ROICs at temperatures below 40 K, there are big technical challenges to construct terahertz photo-type focal plane arrays. In this work, we report pixel-less photo-type terahertz imagers based on the frequency up-conversion technique. The devices are composed of terahertz quantum-well photo-detectors (QWPs) and near-infrared (NIR) light emitting diodes (LEDs) which are grown in sequence on the same substrates using molecular beam epitaxy. In such an integrated QWP-LED device, photocurrent in the QWP drives the LED to emit NIR light. By optimizing the structural parameters of the QWP-LED, the QWP part and the LED part both work well. The maximum values of the internal and external energy up-conversion efficiencies are around 20% and 0.5%. A laser spot of a homemade terahertz quantum cascade laser is imaged by the QWP-LED together with a commercial Si camera. The pixel-less imaging results show that the image blurring induced by the transverse spreading of photocurrent is negligible. The demonstrated pixel-less imaging opens a new way to realize high performance terahertz imaging devices.

SUBMITTER: Fu ZL

PROVIDER: S-EPMC4857121 | biostudies-other | 2016

REPOSITORIES: biostudies-other

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Project description:We report that terahertz (THz) irradiation of mouse mesenchymal stem cells with a pulsed broadband (centered at 10 THz) source, or a single-frequency, 2.52 THz, (SF) laser source, both with weak average power (<1mW/cm2), results in specific heterogenic changes in gene expression. The insignificant differential expression of heat shock and stress related genes as well as our temperature measurements imply a non-thermal response. The microarray survey and RT-PCR experiments demonstrate that at different irradiation conditions distinct groups of genes are activated. Stem cells irradiated for 12 hours with the broadband THz source exhibit an accelerated differentiation toward adipose phenotype, while the 2-hour (broadband or SF) irradiation affects genes transcriptionally active in pluripotent stem cells. Phenotypic and gene expression differences suggest that the THz effect depends on irradiation parameters such as duration and type of THz source, and on the level of stem cell differentiation. Computer simulations of the core promoters of two pluripotency markers reveal association between gene upregulation and propensity for DNA breathing. We propose that THz radiation has potential for non-contact control of cellular gene expression. Growing in petri dish mouse mesenchymal stem cell cultures are irradiated for 2 hours with a single-frequency (2.52 THz) CW laser source. Three independent biological experiments were conducted. In each experiment, a control mMSC culture was placed adjacent to the irradiated sample, and the temperature was kept at 26-27M-BM-:C for both the control and the irradiated sample. Immediately after completing the irradiation, total RNA was extracted from the irradiated sample and the control, and microarrays were used to identify differential changes in gene expression between the irradiated sample and its respective control. In each experiment, the mMSC cultures were synchronized to be at the same differentiation time point immediately before the irradiation.

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Frequency Up-Conversion Photon-Type Terahertz Imager.

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