Quantum imaging using photon pairs offers medical science unprecedented, non-invasive molecular ID
Mid-infrared imaging is opening up exciting possibilities in the biomedical sector, allowing scientists to monitor and identify specific biomolecules such as proteins and lipids in a non-invasive way. These biomolecules can be identified by their unique absorption patterns in the mid-infrared range – their molecular ‘fingerprint’. Despite being a powerful tool for understanding complex biological systems, a significant hurdle is holding back progress – the lack of efficient, high-performance mid-infrared cameras.
Efficient, compact and reliable imaging in the mid-infrared
The EU-funded FastGhost project was established to tackle this challenge, utilising an innovative approach called ghost imaging. Unlike conventional imaging, which relies on standard cameras, ghost imaging uses the connection between photon pairs to create an image. When mid-infrared photons strike an object, they interact with it and gather valuable information about its properties. However, instead of using a traditional mid-infrared camera to capture this data, a single-pixel detector is used. Meanwhile, the ‘partner photon’ that exists in the visible light spectrum is detected by a highly sensitive camera. Correlation of the information from the single-pixel detector and the visible-light camera produces a clear image of the object. FastGhost researchers have advanced ghost imaging in the mid-infrared by improving key components – photon pair sources, single-photon detectors and single-photon avalanche diode (SPAD) cameras.
Laying the groundwork for getting technology to the commercial stage
“We leveraged quantum imaging protocols to alleviate technical hurdles in detecting mid-infrared light efficiently. Exploiting quantum frequency correlations opened up new possibilities for mid-infrared detection using readily available silicon technology,” notes Valerio Flavio Gili, project coordinator. “This approach has important implications for a range of fields including biomedical imaging, microscopy, LIDAR, remote sensing and forensic science.” The success of FastGhost was built on collaboration with companies, universities and research institutes. The project team developed advanced quantum microscopy demonstrators that operate in the mid-infrared. Key achievements included optimising new superconducting nanowire single-photon detectors, designing specialised silicon cameras with SPAD pixels and creating widefield and scanning quantum microscopy set-ups.
Delivering impressive results on all fronts
The superconducting film used to fabricate the single-photon detectors was optimised to extend the wavelength range of current superconducting nanowire detectors operating beyond 2 μm. “The detector demonstrated up to around 70 % efficiency and timing precision of less than 15 ps, both of which far surpass existing benchmarks. These results indicate the extreme boost FastGhost can bring to low-energy single-photon detection in the low-photon-flux regime,” highlights Gili. Significant progress was also made in SPAD array development. “The main advantage of our SPAD is the integration of in-pixel electronics with relatively high fill-factor, specifically aimed at correlation measurements. These advancements could help reshape the imaging market, driving innovation in quantum applications and enabling breakthroughs in low-light environments like biophotonics research,” explains Gili. In terms of photon-pair sources, reaching a large spectral split between mid-infrared and visible photons is challenging. While periodically poled potassium titanyl phosphate (ppKTP) crystals are commonly used for this purpose, their transparency drops above 3.5 µm. “To address this, we utilised a poled lithium niobate (ppLN)-based source to leverage its mid-infrared range up to the cut-off and built onto the material’s well-established performance,” notes Gili. “We also tested silver thiogallate crystals, which enable photon pair generation with wavelengths extending up to aproximately 12 µm. This helps unlock a whole new spectral region for quantum imaging and sensing applications,” concludes Gili.
Keywords
FastGhost, mid-infrared, quantum imaging, single-photon detector, ghost imaging, photon pairs
