Periodic Reporting for period 4 - TIMING (Time-Resolved Nonlinear Ghost Imaging)
Okres sprawozdawczy: 2021-12-01 do 2022-06-30
This proposal addresses major challenges in Terahertz (THz) sensing at the forefront of the experimental and theoretical investigation. The results will have far-reaching implications in complex science while targeting the next generation of THz imagers, acknowledged as unique diagnostic tools in cross-disciplinary fields in light of the THz’s distinctive ability to unambiguously discriminate molecular compounds.
What is the problem being addressed?
The access to the THz electromagnetic band (lying between optical and microwaves in the electromagnetic spectrum) has been limited for a long time by the lack of cost-effective and practical intense sources. However, THz imaging has demonstrated the striking capability of directly resolving the composition of a target with a very high biological compatibility, thanks to the non-ionizing nature of THz waves.
Many important achievements in the THz domain, have been unlocked by a methodology named Time-Domain Spectroscopy (TDS) which became widely available thanks to the recent affordability of lasers emitting very short pulses. The methodology requires the generation of a THz pulse which is then focused on an object. The pulse transmitted through the object, or reflected by it, is collected and its modification reveals a fingerprint of the point of the object illuminated. In principle, by moving the object we can create an image, which reveals the composition of the object at any point. It easy to see how this process can be very slow as it requires a mechanical interaction with the object. In addition, when the object cannot be moved, the solution is to move the THz apparatus (a quite bulky device) in front of it.
Although technology in optical imaging evolved in the form of very-well-integrated arrays of sensors (as available in all modern mobile phones), THz cameras are quite primitive in the general design, and they cannot be adapted to perform spectroscopy.
TIMING is a project and a methodology (namely Time-Resolved Nonlinear Ghost Imaging), that address this scenario, and has an impact on all wave-domains difficult to access.
Why is it important for society?
The emergence of THz as an independent science can be directly related to the increased need in biology, security, environmental monitoring and industry in general for low-cost technologies that allow fast, standoff and in situ chemical analysis. Bio-matter, like proteins, aminoacids and DNA, possesses specific resonances in the THz band. Moreover, many materials are quite transparent to terahertz waves (clothes, many types of fabric, plastics). Hence, the deployment of terahertz technologies has obvious critical implications in security, assessment of chemical hazards, life-science.
What are the overall objectives?
TIMING develops a consistent programme for statistical imaging via nonlinear optical conversion. In essence, it develops around two basic ideas: (i) it is possible to perform an image of object illuminating the object with many different radiation patterns and then collecting radiation from it using a single point detector (i.e. no need of cameras at any stage). This general approach is widely addressed in literature as Ghost Imaging. (ii) To circumvent the difficulties in accessing a specific frequency domain (in our case, terahertz), the patterns are created at an optical frequency and then converted into THz using a so-called 'Nonlinear Optical Conversion'. This second aspect is key and sharply discriminates this approach from the state of the art. TIMING provides the fundamental proof of concept of this idea.
What is the problem being addressed?
The access to the THz electromagnetic band (lying between optical and microwaves in the electromagnetic spectrum) has been limited for a long time by the lack of cost-effective and practical intense sources. However, THz imaging has demonstrated the striking capability of directly resolving the composition of a target with a very high biological compatibility, thanks to the non-ionizing nature of THz waves.
Many important achievements in the THz domain, have been unlocked by a methodology named Time-Domain Spectroscopy (TDS) which became widely available thanks to the recent affordability of lasers emitting very short pulses. The methodology requires the generation of a THz pulse which is then focused on an object. The pulse transmitted through the object, or reflected by it, is collected and its modification reveals a fingerprint of the point of the object illuminated. In principle, by moving the object we can create an image, which reveals the composition of the object at any point. It easy to see how this process can be very slow as it requires a mechanical interaction with the object. In addition, when the object cannot be moved, the solution is to move the THz apparatus (a quite bulky device) in front of it.
Although technology in optical imaging evolved in the form of very-well-integrated arrays of sensors (as available in all modern mobile phones), THz cameras are quite primitive in the general design, and they cannot be adapted to perform spectroscopy.
TIMING is a project and a methodology (namely Time-Resolved Nonlinear Ghost Imaging), that address this scenario, and has an impact on all wave-domains difficult to access.
Why is it important for society?
The emergence of THz as an independent science can be directly related to the increased need in biology, security, environmental monitoring and industry in general for low-cost technologies that allow fast, standoff and in situ chemical analysis. Bio-matter, like proteins, aminoacids and DNA, possesses specific resonances in the THz band. Moreover, many materials are quite transparent to terahertz waves (clothes, many types of fabric, plastics). Hence, the deployment of terahertz technologies has obvious critical implications in security, assessment of chemical hazards, life-science.
What are the overall objectives?
TIMING develops a consistent programme for statistical imaging via nonlinear optical conversion. In essence, it develops around two basic ideas: (i) it is possible to perform an image of object illuminating the object with many different radiation patterns and then collecting radiation from it using a single point detector (i.e. no need of cameras at any stage). This general approach is widely addressed in literature as Ghost Imaging. (ii) To circumvent the difficulties in accessing a specific frequency domain (in our case, terahertz), the patterns are created at an optical frequency and then converted into THz using a so-called 'Nonlinear Optical Conversion'. This second aspect is key and sharply discriminates this approach from the state of the art. TIMING provides the fundamental proof of concept of this idea.
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.
The status of the project can be summarised as follows (some details and data are still at the confidential level and will be disclosed in due time).
WP1 The investigation on the nonlinear transformations relating the optical and THz patterns for sub-wavelength THz Computational Imaging
-Theoretical foundation (WP1.1): we completed the theoretical foundation of the Nonlinear Ghost Imaging developing the necessary background for the methodology.
This includes a major publication (published in ACS Photonics 5(8), 3379–3388 (2018)) using typical terahertz waveforms emitted by experimental sources. The core element of this achievement is the prediction of how a statistic pattern of light is converted into THz and then propagates reaching the target.
Most notably, we determined that TIMING is immune from an uncorrectable aberration usually occurring in high-resolution THz-imaging approaches based on time-domain-spectroscopy.
-The experimental foundation (WP1.2-WP1.3) is completed. We built an experimental test-bench for the project. In particular, the specific technical requirements of the methodology brought to the development of novel thin optical-to-THz converters (the precursory work is published in Nano Energy 46, 128–132 (2018)). It is worth noting that parts of this development are considered for IP protection and resulted in the spin-out ERC-PoC project "THINK".
-WP2 Formalization and demonstration of the Time-Resolved Nonlinear Ghost Imaging (TIMING)
WP2.1 The theoretical foundation of TIMING is approaching completion.
WP2.2 The full imaging experimental demonstration of the imaging system with a demonstrator is approaching completion. We delivered the first terahertz image ever produced via a nonlinear ghost imaging system [arXiv:1910.11259 [physics] (2019). – in publications on OPTICA].
The long terahertz wavelength (about 0.3mm) makes the requirement of subwavelength resolution (i.e. obtaining information on details smaller than the terahertz wavelength) in imaging quite general in applications. In our theoretical investigation (WP1.1 and WP2.1 currently ongoing) we discovered that all the previous computational imaging approaches proposed for the reconstruction of time-domain terahertz images are prone to an important deterministic error at high (subwavelength) resolution. Conversely, we demonstrated the TIMING allows the imaging with high resolution and fidelity using a novel methodology we refer as "spatio-temporal refocusing" [arXiv:1910.11259 [physics] (2019). – in publications on OPTICA].
-The activity of WP3 is expected to start in June 2020
The status of the project can be summarised as follows (some details and data are still at the confidential level and will be disclosed in due time).
WP1 The investigation on the nonlinear transformations relating the optical and THz patterns for sub-wavelength THz Computational Imaging
-Theoretical foundation (WP1.1): we completed the theoretical foundation of the Nonlinear Ghost Imaging developing the necessary background for the methodology.
This includes a major publication (published in ACS Photonics 5(8), 3379–3388 (2018)) using typical terahertz waveforms emitted by experimental sources. The core element of this achievement is the prediction of how a statistic pattern of light is converted into THz and then propagates reaching the target.
Most notably, we determined that TIMING is immune from an uncorrectable aberration usually occurring in high-resolution THz-imaging approaches based on time-domain-spectroscopy.
-The experimental foundation (WP1.2-WP1.3) is completed. We built an experimental test-bench for the project. In particular, the specific technical requirements of the methodology brought to the development of novel thin optical-to-THz converters (the precursory work is published in Nano Energy 46, 128–132 (2018)). It is worth noting that parts of this development are considered for IP protection and resulted in the spin-out ERC-PoC project "THINK".
-WP2 Formalization and demonstration of the Time-Resolved Nonlinear Ghost Imaging (TIMING)
WP2.1 The theoretical foundation of TIMING is approaching completion.
WP2.2 The full imaging experimental demonstration of the imaging system with a demonstrator is approaching completion. We delivered the first terahertz image ever produced via a nonlinear ghost imaging system [arXiv:1910.11259 [physics] (2019). – in publications on OPTICA].
The long terahertz wavelength (about 0.3mm) makes the requirement of subwavelength resolution (i.e. obtaining information on details smaller than the terahertz wavelength) in imaging quite general in applications. In our theoretical investigation (WP1.1 and WP2.1 currently ongoing) we discovered that all the previous computational imaging approaches proposed for the reconstruction of time-domain terahertz images are prone to an important deterministic error at high (subwavelength) resolution. Conversely, we demonstrated the TIMING allows the imaging with high resolution and fidelity using a novel methodology we refer as "spatio-temporal refocusing" [arXiv:1910.11259 [physics] (2019). – in publications on OPTICA].
-The activity of WP3 is expected to start in June 2020
We can summarise the progress beyond the state of the art in the following points
(i)The first terahertz images ever produced with a nonlinear ghost imaging system. One relevant example has been produced using a biological sample (a leaf).
(ii)The demonstration that a nonlinear single-pixel imaging approach circumvents classical imaging resolution limits and allows high fidelity hyperspectral imaging.
(iii) The generation of novel IP related to novel thin terahertz emitters.
Before the end of the project, we expect to produce a versatile terahertz imager demonstrator deployable in many challenging scenarios.
(i)The first terahertz images ever produced with a nonlinear ghost imaging system. One relevant example has been produced using a biological sample (a leaf).
(ii)The demonstration that a nonlinear single-pixel imaging approach circumvents classical imaging resolution limits and allows high fidelity hyperspectral imaging.
(iii) The generation of novel IP related to novel thin terahertz emitters.
Before the end of the project, we expect to produce a versatile terahertz imager demonstrator deployable in many challenging scenarios.