Time-Resolved Nonlinear Ghost Imaging

Project Information

TIMING

Grant agreement ID: 725046

DOI

10.3030/725046

Project closed

EC signature date 27 March 2017

Start date 1 June 2017

End date 30 September 2023

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 979 270,00

EU contribution

€ 1 979 270,00

Coordinated by

LOUGHBOROUGH UNIVERSITY
United Kingdom

Periodic Reporting for period 5 - TIMING (Time-Resolved Nonlinear Ghost Imaging)

Reporting period: 2022-07-01 to 2023-09-30

Summary of the context and overall objectives of the project

What is the problem being addressed?
The TIMING project addresses critical limitations in current imaging technologies, particularly in the Terahertz (THz) frequency range. Traditional imaging methods struggle in this spectrum due to technological constraints and the complex nature of THz wave interactions with materials. This gap in effective THz imaging limits our ability to explore and understand a range of materials and biological systems. Most importantly, TIMING aim to provide an imaging approach that preserves with fidelity the spectral fingerprint of a target (its physical/chemical composition) while allowing agile access to resolution not constrained by the course by the typical diffraction limit of traditional imaging systems that, at THz cannot resolve anything smaller than a grain of salt. This gap hinders advancements in various fields, from material science to biomedical imaging.

Why is it important for society?
THz imaging is pivotal for society due to its wide range of applications. It can advance medical diagnostics via non-invasive imaging techniques, enhance security screening removing health risks connected to ionizing radiation, and offer new insights in material science, art conservation, and environmental monitoring. Novel THz imaging technology can lead to breakthroughs in these areas.

What are the overall objectives?
The primary objective of TIMING is to develop a novel THz imaging approach based on the principle of Nonlinear Ghost Imaging, conceived for the project and demonstrated through it. This approach shifts the complexity of electromagnetic pattern control from the THz to the optical level, enabling the exposure of a target to dense morphology THz waves. This pushes the resolution beyond the THz diffraction limit, a key constraint for Terahertz imaging applications.

A further objective is to exploit this arbitrary illumination to implement a scattering-aided imaging approach, which is the exploitation of the disorder of the optical systems (normally considered detrimental to the propagation of light) to enhance several imaging properties.

The introduction of Nonlinear Ghost Imaging is a pivotal innovation with implications beyond the THz band. It opens up new possibilities in imaging across various frequency ranges and domains, particularly where array imaging technologies underperform. This methodology not only enhances the resolution and capabilities of THz imaging but also paves the way for new imaging techniques in other frequency bands. TIMING is not just about advancing THz imaging; it's about setting a new standard in imaging technology across the spectrum, with profound implications for scientific research, societal applications, and technological innovation.

The project successfully pursued the desired investigation and delivered the planned objectives.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project comprises three principal work packages (WP1, WP3 and WP3) that represent the steps (i) formalisation and demonstration of the background concepts (ii) demonstration of the imaging approach and its features (iii) application of the imaging approach to challenging terahertz imaging scenarios.

WP1 completed the investigation on the nonlinear transformations relating the optical and THz patterns for sub-wavelength THz Computational Imaging
It is worth noting that parts of this development are now in progress for IP protection and resulted in the spin-out ERC-PoC project "THINK" for the exploitation of this IP.
WP2 completed the formalization and demonstration of the Time-Resolved Nonlinear Ghost Imaging .
WP3 Investigated Complex Media and superfocusing in the context of the Nonlinear Ghost Imaging.
The theoretical study about the deterministic and statistical approaches to boost imaging through a scattering media and gain spatiotemporal control of the scrambled light transmitted is completed. The experimental demonstration of deterministic wave control and imaging through scattering media is also completed.

Overview of the results and their exploitation and dissemination

The team explored the control of THz-patterned illumination using spatial light modulators and extended these findings to illumination patterns with delay distributions. The experimental foundation laid down, particularly the work on sub-wavelength illumination definition, demonstrated the feasibility of super-wavelength (space-time) and sub-wavelength imaging of samples in near-field coupling with a terahertz emitter. In the context of the experimental realisation, it explored suitable technologies for the generation and conditioning of Terahertz waves in the context of Terahertz Imaging, (Optica 4(11), 1358 (2017), IEEE Photon. Technol. Lett. 30(17), 1579–1582 (2018), Physical Review A 99(5), (2019), Sensors 22(23), 9432 (2022)). During the project implementation, the team also explored the physics of systems with reduced dimensionality (surfaces or quasi-2D materials) for their typical low thickness (high efficiency per unit of length), as the project determined the correlation between the thickness of the terahertz generators with the quality of near-field imaging (Nano Energy 46, 128–132 (2018), Micromachines 11(5), 521 (2020), Rev. Research 3(4), L042006 (2021), Phys. Rev. Lett. 125(26), 263901 (2020), Advanced Optical Materials 11(15), 2202578 (2023)).

The project delivered the theoretical and experimental foundation of the Nonlinear Ghost Imaging (ACS Photonics 5(8), 3379–3388 (2018)). The experimental campaigns demonstrated the operation of Nonlinear Ghost Imaging in real media and its performance against classical sources of noise (Optica 7(2), 186 (2020)) and the ability to perform microscopic THz tomographic images (ACS Photonics 10(6), 1726–1734 (2023))

The final stage of the project focused on generalizing Nonlinear Ghost Imaging for propagation in complex media. The theoretical and experimental demonstrations achieved spatiotemporal superfocusing, showing that a scattering medium could reshape the field with sub-wavelength spatial definition (Open Res Europe 2, 32 (2022), ACS Photonics 9(8), 2634–2642 (2022)). The culmination of this work is the ground-breaking demonstration of terahertz spatiotemporal wave synthesis exploiting disordered systems (ACS Photonics acsphotonics.3c01671 (2024)).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We can summarise the progress beyond the state of the art in the following points

(i)The first terahertz image with a nonlinear ghost imaging system. One relevant example has been produced using a biological sample (a leaf).

(ii)The demonstration that the Nonlinear Ghost Imagingcircumvents classical imaging resolution limits and allows high-fidelity hyperspectral imaging.

(iii) The generation of novel IP related to novel thin terahertz emitters.

(iv) Definition and experimental demonstration of the first volumetric microscopic imaging methodology based on the terahertz sparse illumnination.

(v) The first demonstration of field-level arbitrary Terahertz wave synthesis based on propagation through complex media.

Rappresentation of the Nonlinear Ghost Imaging (L. Olivieri, ACS Photonics 5(8), 3379–3388 (2018))