Periodic Reporting for period 2 - FastGhost (Fast quantum ghost microscopy in the mid-infrared)
Período documentado: 2021-10-01 hasta 2024-06-30
Imaging in the mid-IR range enables the chemically selective monitoring of biomolecules such as proteins and lipids. They can be identified by their characteristic absorption spectra in this specific spectral range. Therefore, biomedical imaging can greatly benefit from development in this area. However, there is a significant lack of efficient high-performance cameras in the mid-IR range, which hinders such utilization.
This is exactly where FastGhost offers new perspectives. Based on the quantum ghost imaging scheme, a new quantum imaging approach for the mid-IR is developed, in particular the essential components for implementation. Quantum ghost imaging is based on photon pair sources that provide correlated photon pairs. These can have different spectral properties. In FastGhost, an object is illuminated by mid-IR photons, which are afterwards detected not by a camera but by a single-pixel detector. In parallel, the visible partner photon (from the mid-IR-visible photon pair) is detected by a highly sensitive spatially resolving camera. The camera is correlated with the single pixel detector and thus, an image of the object is obtained. This is sketched in an attached figure. In order to allow efficient, compact, and reliable quantum ghost imaging in the mid-IR, further development on the essential components such as the photon pair source, the camera, and the single pixel detector are indispensable. Hence, FastGhost tackles these developments and verifies their impact by demonstrating fast quantum ghost imaging in the mid-IR.
So far, such quantum ghost imaging schemes suffered from the fact that both photons needed to be detected in a synchronous way, meaning to deliver a coincidence event in a fixed (and small) time slot. This necessitated the use of intricate image preserving optical delay lines for the visible photons. Therefore, compact and practicable setups had not been possible. The development of a SPAD-camera allowing for asynchronous detection (they can occur at any time, and the sensor must be always ready to detect them) with a high precision (down to fractions of a billionth of a second) is one part of FastGhost.
Summarize, the objectives of FastGhost are:
1. Demonstrating quantum ghost imaging in the mid-IR.
2. Development of photon pair sources with one photon in the visible and its partner in the mid-IR.
3. Development of single-photon detector in the mid-IR
4. Development of SPAD-camera for asynchronous detection.
This is exactly where FastGhost offers new perspectives. Based on the quantum ghost imaging scheme, a new quantum imaging approach for the mid-IR is developed, in particular the essential components for implementation. Quantum ghost imaging is based on photon pair sources that provide correlated photon pairs. These can have different spectral properties. In FastGhost, an object is illuminated by mid-IR photons, which are afterwards detected not by a camera but by a single-pixel detector. In parallel, the visible partner photon (from the mid-IR-visible photon pair) is detected by a highly sensitive spatially resolving camera. The camera is correlated with the single pixel detector and thus, an image of the object is obtained. This is sketched in an attached figure. In order to allow efficient, compact, and reliable quantum ghost imaging in the mid-IR, further development on the essential components such as the photon pair source, the camera, and the single pixel detector are indispensable. Hence, FastGhost tackles these developments and verifies their impact by demonstrating fast quantum ghost imaging in the mid-IR.
So far, such quantum ghost imaging schemes suffered from the fact that both photons needed to be detected in a synchronous way, meaning to deliver a coincidence event in a fixed (and small) time slot. This necessitated the use of intricate image preserving optical delay lines for the visible photons. Therefore, compact and practicable setups had not been possible. The development of a SPAD-camera allowing for asynchronous detection (they can occur at any time, and the sensor must be always ready to detect them) with a high precision (down to fractions of a billionth of a second) is one part of FastGhost.
Summarize, the objectives of FastGhost are:
1. Demonstrating quantum ghost imaging in the mid-IR.
2. Development of photon pair sources with one photon in the visible and its partner in the mid-IR.
3. Development of single-photon detector in the mid-IR
4. Development of SPAD-camera for asynchronous detection.
FastGhost tackles the challenges for implementing fast quantum ghost imaging in the mid-IR. In the first 12 months of the project, great progress was achieved for all components as well as for the complete imaging scheme.
In detail, for realizing a single-photon single-pixel detector in the mid-IR, essential first steps have been implemented. The detection system is based on superconducting nanowires. There, a superconducting thin film is the linchpin of the system and is normally not sensitive for the targeted spectral range. In FastGhost, such superconducting films could be developed exhibiting a high performance in the mid-IR range for the first time. Based on these films, a first detection system could be implemented. It demonstrated mid-IR detection with 70% system detection efficiency and < 15 ps timing. Both are superior values and are signs of the extreme boost FastGhost brings into the field of single-photon detection in the low-energy regime.
The same steep progress holds for the SPAD-array development. Starting with the implementation of a theoretical model to validate the “look back” correlation method, schematized in Figure 1. The SPAD trigger is delayed by almost the same propagation delay of the trigger bucket detector. The correlation network generates a correlation window starting from the SPAD trigger with a duration of few ns and the correlation is detected if the correlation window and the bucket detector are overlapped. Figure 2 shows the results of the theoretical model with 100k acquisitions including also the SPAD dark count noise. For experimental realization two approaches have been considered: First, in-pixel correlation architecture having the correlation logic at each pixel. And second, event-driven architecture, where the correlation happens in the periphery. Three different pixel architectures (the two described above and a mix of both) are shown in Figure 3.
The development of dedicated SPAD arrays, combined with the “look-back principle” allowed to perform fast widefield quantum ghost imaging at 1.4 µm, see Figure 4. A larger SPAD imager with 472x456 was developed, and quantum correlations were observed on it. In parallel, a scanning approach was also pursued, to make use of readily usable SNSPDs working up to 2 µm. This led to the successful implementation of quantum ghost imaging of relevant bio-medically relevant samples such as neck tissue and HEK 293T cell samples (Figure 5), and thanks to the wavelength tunability of the employed photon-pair source, a lithium niobate waveguide, we could demonstrate hyperspectral scanning ghost imaging (Figure 6).
For ghost imaging implementations deeper in the MIR, a SNSPD at 4 µm with an efficiency between 5% and 15%, corresponding to dark count rates (DCR) of respectively 2.33 MHz and 5.20 MHz. This detector was integrated in a ghost imaging setup at IOF, however doe to technical issues in terms of:
• Single-mode fiber-coupling of a highly diverging Mid-IR beam.
• Noise contribution from thermal radiation.
• Losses through the Mid-IR optical path.
• The obtainable signal is lower than the fluctuations in the detector.
For the same reasons, a SNSPD detector up to 7 µm was not developed.
In detail, for realizing a single-photon single-pixel detector in the mid-IR, essential first steps have been implemented. The detection system is based on superconducting nanowires. There, a superconducting thin film is the linchpin of the system and is normally not sensitive for the targeted spectral range. In FastGhost, such superconducting films could be developed exhibiting a high performance in the mid-IR range for the first time. Based on these films, a first detection system could be implemented. It demonstrated mid-IR detection with 70% system detection efficiency and < 15 ps timing. Both are superior values and are signs of the extreme boost FastGhost brings into the field of single-photon detection in the low-energy regime.
The same steep progress holds for the SPAD-array development. Starting with the implementation of a theoretical model to validate the “look back” correlation method, schematized in Figure 1. The SPAD trigger is delayed by almost the same propagation delay of the trigger bucket detector. The correlation network generates a correlation window starting from the SPAD trigger with a duration of few ns and the correlation is detected if the correlation window and the bucket detector are overlapped. Figure 2 shows the results of the theoretical model with 100k acquisitions including also the SPAD dark count noise. For experimental realization two approaches have been considered: First, in-pixel correlation architecture having the correlation logic at each pixel. And second, event-driven architecture, where the correlation happens in the periphery. Three different pixel architectures (the two described above and a mix of both) are shown in Figure 3.
The development of dedicated SPAD arrays, combined with the “look-back principle” allowed to perform fast widefield quantum ghost imaging at 1.4 µm, see Figure 4. A larger SPAD imager with 472x456 was developed, and quantum correlations were observed on it. In parallel, a scanning approach was also pursued, to make use of readily usable SNSPDs working up to 2 µm. This led to the successful implementation of quantum ghost imaging of relevant bio-medically relevant samples such as neck tissue and HEK 293T cell samples (Figure 5), and thanks to the wavelength tunability of the employed photon-pair source, a lithium niobate waveguide, we could demonstrate hyperspectral scanning ghost imaging (Figure 6).
For ghost imaging implementations deeper in the MIR, a SNSPD at 4 µm with an efficiency between 5% and 15%, corresponding to dark count rates (DCR) of respectively 2.33 MHz and 5.20 MHz. This detector was integrated in a ghost imaging setup at IOF, however doe to technical issues in terms of:
• Single-mode fiber-coupling of a highly diverging Mid-IR beam.
• Noise contribution from thermal radiation.
• Losses through the Mid-IR optical path.
• The obtainable signal is lower than the fluctuations in the detector.
For the same reasons, a SNSPD detector up to 7 µm was not developed.
FastGhost has realized quantum ghost imaging in the mid-IR, which enables a variety of applications, especially in the biomedical imaging sector. Along these lines, the development of the essential components themselves will foster a broader application of photonic quantum technology far beyond quantum ghost imaging.
In detail, the realization of high-performance mid-infrared single-photon detectors in terms of efficiency and timing resolution will enable applications such as environmental sensing or long wavelength (quantum) communication. So far, such systems have been limited to efficiently work below 1700 nm. In FastGhost, the superconducting film used to fabricate the single-photon detectors was optimized to extend the wavelength range of the superconducting nanowire detectors. Furthermore, the newly developed mid-IR detectors efficiently working beyond 2 µm.
Photon pair sources covering the mid-IR can be harnessed for various quantum sensing applications such as quantum imaging with undetected light or hyperspectral correlation-based imaging. FastGhost partners have successfully realized photon-pair sources able to operate up to 14 µm.
SPAD-arrays are used as highly sensitive camera in both domains, for classical imaging and sensing as well as for quantum imaging. With their timing and thus correlation capability, they are a crucial tool for all correlation-based imaging approaches. Hence, their advancement will beneficially impact the imaging market, especially in the quantum regime and in the low-light biophotonics regime. Within FastGhost, SPAD arrays with up to 472x456 pixels, fill factor up to 31%, 17 µm pitch embedding correlation electronics, Short and precise correlation window from 1 ns to 15 ns, maximum correlation rate of 30 MHz.
In detail, the realization of high-performance mid-infrared single-photon detectors in terms of efficiency and timing resolution will enable applications such as environmental sensing or long wavelength (quantum) communication. So far, such systems have been limited to efficiently work below 1700 nm. In FastGhost, the superconducting film used to fabricate the single-photon detectors was optimized to extend the wavelength range of the superconducting nanowire detectors. Furthermore, the newly developed mid-IR detectors efficiently working beyond 2 µm.
Photon pair sources covering the mid-IR can be harnessed for various quantum sensing applications such as quantum imaging with undetected light or hyperspectral correlation-based imaging. FastGhost partners have successfully realized photon-pair sources able to operate up to 14 µm.
SPAD-arrays are used as highly sensitive camera in both domains, for classical imaging and sensing as well as for quantum imaging. With their timing and thus correlation capability, they are a crucial tool for all correlation-based imaging approaches. Hence, their advancement will beneficially impact the imaging market, especially in the quantum regime and in the low-light biophotonics regime. Within FastGhost, SPAD arrays with up to 472x456 pixels, fill factor up to 31%, 17 µm pitch embedding correlation electronics, Short and precise correlation window from 1 ns to 15 ns, maximum correlation rate of 30 MHz.