Context:

High-resolution spectroscopic imaging in the THz domain represents a critical frontier for future space-based astronomical observations. The development of multi-pixel heterodyne receiver technology is essential to unlock the full scientific potential of next-generation far-infrared telescopes.

Observatoire de Paris, through LIRA laboratory, is actively involved in the preparation of LETO (Line Emission Terahertz Observatory), a promising far-infrared space mission concept. LETO aims to perform velocity-resolved spectroscopic observations of key lines in the THz range, particularly the [CI] line at 1.9 THz, crucial for understanding the interstellar medium and star formation processes. Future missions like LETO will require multi-pixel heterodyne arrays to achieve sufficient mapping speed and observing efficiency, representing a major technological leap from the single-pixel receivers flown on Herschel/HIFI.

Among all mixer technologies, Superconducting Hot Electron Bolometer (HEB) mixers demonstrate the best performance beyond 1 THz, with noise temperatures approaching the quantum limit. HEB mixers have proven reliable in space (Herschel) and airborne missions (SOFIA). LIRA has extensive experience with HEB mixers, achieving state-of-the-art sensitivities at 1.3 and 2.5 THz on single-pixel receivers. Building on this heritage, as well as on ground-based arrays, we now aim to develop the first multi-pixel architectures suitable for future space missions.

Work description:

Heterodyne camera realization is significantly more complex than direct detection systems, requiring efficient coupling of RF signal and local oscillator (LO), plus optimal intermediate frequency (IF) extraction. HEB mixers operating at cryogenic temperatures (around 4 K) are sensitive to bias fluctuations and LO instability, requiring careful system design for space applications.

This thesis will investigate innovative solutions for integrating HEB mixers into a compact multi-pixel receiver architecture. The work will focus on multi-pixel integration challenges, exploring several technological approaches depending on scientific priorities and mission constraints.

A key challenge is the LO distribution architecture for delivering stable, uniform power to multiple mixer elements. Different solutions will be studied: quasi-optical beam-divider systems allowing flexible pixel arrangements, or waveguide-based distribution networks enabling compact integration. Each approach presents specific advantages regarding efficiency, uniformity, complexity, and space qualification. Trade-off studies combining electromagnetic simulations and experimental validations will guide the technology selection.

The IF signal transmission from multiple pixels to cryogenic low-noise amplifiers (LNAs) constitutes another critical aspect. For an array, efficient signal routing, impedance matching, and compact integration must be carefully optimized to preserve high sensitivity while minimizing mass and volume. Integration strategies for IF amplification and multiplexing will be investigated to meet the specific requirements of multi-pixel operation.

The work will include design and simulation. A prototype will be manufactured with the means of a clean room and a mechanical workshop by technically competent staff with whom the work of the thesis should be in close collaboration. Cryogenic testing of the prototype will be carried out at 4 K, including the characterization of key performance parameters: noise temperature, RF bandwidth, IF bandwidth, LO power requirements, and system stability.

Expected results:

This thesis will deliver a comprehensive study of multi-pixel HEB receiver architectures optimized for 1.9 THz, technological solutions for LO distribution and IF signal management, and a prototype demonstrating performance suitable for future THz space missions. The outcomes will contribute to advancing the instrumentation for missions like LETO and establish foundations for future multi-pixel THz receivers for space applications.

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For more Information about the topics and the co-financial partner (found by the lab!); contact Directeur de thèse - martina.wiedner@obspm.fr

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online before March 13th, 2026 Midnight Paris time!