Miniaturized All Solid-state Terahertz HEterodyne Receiver for security applications – MASTHER

In the context of applicability of very compact coherent detection systems in the potentially rich THz market, MASTHER aims at implementing a heterodyne receiver built from a hot electron bolometer (HEB) sensitive mixing chip in a light cooler (80 K) combined with a THz quantum cascade laser (QCL) solid-state source operating at 60 K as a local oscillator; the HEB mixer and the QCL source will be each installed in their own miniaturized cryo-cooler. MASTHER will be a mobile THz detection system with good sensitivity at low cost.
The consortium partners are: LGEP (SUPELEC-CNRS-Univ. UPMC Paris 6 and Paris 11), Coordinator, with CEA-INAC (subcontractor); UMPhy (Thales-CNRS); MPQ (Univ. Paris-Diderot CNRS) and Thales Research & Technology.
The MASTHER project involves five tasks: 1) coordination (LGEP); 2) growth of high temperature superconductor material (YBaCuO) and HEB physics (LGEP / UMPhy CEA); 3) design, realization and laboratory tests of YBaCuO HEB mixers (LGEP); 4) design, realization and tests of THz QCL sources (MPQ), 5) integration and demonstration of a prototype (TRT). In practice, MASTHER combines the expertise of four partners, who have started working closely with each other and are to maintain this close collaboration during the whole duration of this industrial project.

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Task 1: project coordination by LGEP.
Task 2: optimization of YBaCuO thin film growth and understanding of physical mechanisms of HEB devices (coordination: LGEP). This task aims at producing ultrathin films (10-40 nm) to achieve high quality HEB devices. Two strategies will be considered: i) sputtering deposition performed at CEA-INAC in Grenoble (subcontractor of LGEP), ii) laser ablation deposition at UMPhy. Physics of HEB will also be considered to optimize the device geometry.
Task 3: realization of THz HEB frequency mixers and functional tests (coordination: LGEP). This task aims at providing a HEB chip for the final miniaturized THz receiver MASTHER demonstrator. All designs related to the mixer (THz optical front end, HEB structure of the chip, back end for microwave signal at the intermediate frequency) will be performed at LGEP in relation with the other partners. Preliminary HEB testing and THz mixing tests in an ad hoc cryostat will be conducted at LGEP.
Task 4: design, realization and test of QCL THz sources (coordination: MPQ). This task aims at providing two types of sources: a conventional multimode source for THz mixing tests at LGEP (Task 3) and a single mode source specifically dedicated to the MASTHER demonstrator in a miniaturized micro-cooler at TRT (Task 5).
Task 5: integration of the prototype and demonstration of the MASTHER THz detection system (coordination: TRT). This work aims at integrating the HEB mixer in its own miniature cryostat (80 K) and also the THz QCL source in another similar cryostat (60 K). It includes designing the whole system, designing the mixer block and the associated microwave cryo-electronics, developing two miniaturized cooling modules, integrating the MASTHER system and testing it for demonstrating thermal detection of an object located at a few meters.

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Since the first demonstration in 2002-2003, of the solid-state quantum cascade laser (QCL) operating at terahertz frequencies (THz, typically spanning from 500 GHz to 5000 GHz), there has been a great renewal of interest for this part of the spectrum, especially for security, non-destructive testing, environmental, pharmaceutical and medical applications. For security indeed, ambitious projects have been supported to date which, from a scientific and technical point of view, provided excellent results. Unfortunately the demonstrations were obtained with a too moderate applicability: although overall systems have proven unique potential in this field, they remained complex, bulky and mostly unable to demonstrate real time operation, especially for remote detection. Furthermore, one can believe that the lack of really operational systems mainly results from too limited efforts towards the realisation of compact and high performance THz sensing module chains.
At the same time, heterodyne THz detectors/mixers based on superconducting hot electron bolometers (HEB) have been optimized for radio-astronomy, to reach ultimate sensitivity close to a few THz photons per second, but with the drawback of cryogenic cooling down to 4 K.
The alternative solution for high sensitivity heterodyne detection at 300 K is to use Schottky diodes. In this case limitations come from the power level required of the local oscillator (LO), increasing with frequency up to some mW at 2 THz (compared to a few tens of nW with a HEB). So it becomes difficult to address all the frequency range of interest for security applications.
In between 4 K and 300 K, high critical temperature superconducting (HTS) materials, operating around 77 K, have reached a high level of maturity that permits implementation of high performance microwave devices. Moreover, these devices can be implemented in very compact closed circuit cryogenic coolers (about 400 cm3).
According to these considerations we believe that: (i) a highly sensitive, compact and easy-to-use THz detector is the missing building block which could warrant, beyond the implementation of THz remote sensing systems, the advent of really applicable THz systems; (ii) such a compact and high performance THz (coherent) detector could result from the combination of the existing knowledge on HEB mixer design with the high quality of nowadays HTS materials; (iii) compactness and usability of the final THz coherent detector will benefit from the compactness of closed circuit cryocoolers around 70 K in which it will be possible to implement a HTS HEB mixer, and a THz QCL LO source, as well.
In this applicability context of very compact coherent detection systems to the potentially wealthy market of THz detection, MASTHER aims at implementing a heterodyne receiver made from a sensitive lightweight cooled (80 K) HEB mixer chip with its solid state THz QCL source (at 60 K) as local oscillator in miniaturized cryocoolers. MASTHER will be therefore a portable THz detection system with good sensitivity and reduced cost.
The partners of the proposed consortium are: LGEP (SUPELEC-CNRS-Univ. UPMC Paris 6 and Paris Sud 11), coordinator, with CEA-INAC (sub-contractor); UMPhy (Thales-CNRS); MPQ (Univ. Paris Diderot-CNRS) and Thales Research & Technology. The MASTHER project comprises 5 tasks: 1) Coordination (LGEP), 2) HTS (YBaCuO material) growth and HEB physics (LGEP/CEA & UMPhy), 3) Realization of YBaCuO HEB mixers and laboratory tests (LGEP), 4) Realization of QCL THz sources and tests (MPQ), 5) Integration and MASTHER prototype demonstration (TRT). In practice, it will combine expertise of the 4 partners, which will closely interact with each other during the whole duration of this industrial project.
At the end, a miniaturized all solid state 2.5 THz receiver should be integrated and available for test to exhibit the capability of detecting an object of 10 to 20 degrees differential temperature range at a few metres distance.