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Quantum Spectroscopy

Quantum technology could also revolutionise spectroscopy.  Light can provide information about medically relevant quantities not readily detectable by nuclear magnetic resonance (NMR), ultrasound or X-rays, such as tissue oxygenation linked to stroke or heart attacks.

This project is looking at optical imaging at tissue depths unreachable by other optical methods. This is achieved by ultrasound and light interacting in the measurement region of interest. The increased measurement depth is enabled by quantum-designed structures which only transmit light that has interacted with the ultrasound. The quantum structures have a large area (cm2), accept light for all input angles and slow down the signal ~100,000 times. This means that stray light can be eliminated, giving a stronger signal.

Contact – Researchers

Stefan Kröll, photo by Kennet Ruona.

Stefan Kröll was born in Lysekil, a small town on the Swedish west coast. He graduated with an exam in Engineering Physics from Lund University and then decided to pursue a PhD in the field of laser spectroscopy under the supervision of Sune Svanberg, who had pioneered the field in Sweden.

With the exception of two year-long visits at the University of Colorado in Boulder, CO, and SRI International (former Stanford Research Institute) in Menlo Park, CA, and some shorter guest professor visits in Paris, Kröll has been employed at Lund University since his graduation. After the PhD in experimental laser spectroscopy, he engaged in theoretical work on combustion diagnostics and in particular acquired experience in the non-linear optics area.

During a year at SRI, returning to experimental work, he found an interest in rare earth ion-doped crystals. In particular, their ability to remain in quantum mechanical superposition states over exceptionally long times appeared very intriguing. Back in Lund, he started a research group on non-linear coherent optical interactions in rare earth ion-doped crystals. 1999 he was promoted to professor in Atomic Physics at Lund University.

The research group had already earlier turned their interest to quantum information in rare earth-doped crystals and were pioneers and one of the leading in the field during the first decade of the 20th century. In particular, they introduced methods for quantum state storage and quantum state processing in rare earth ion-doped crystals. During the second decade, the group acquired an interest in slow light techniques enabled by the optical pumping techniques in the rare earth crystals that the group had developed.

Kröll at this time also engaged in management at the departmental and faculty level. Spending three years as Head of the physics department and 6 years on the faculty board. Out of the projects emerging from the slow light activities, one is concerned with developing a technique for optical imaging deep into tissue by combing light and ultrasound (Ultrasound Optical tomography, UOT).

The Atomic physics division already had a long experience of cooperation with groups at the medical faculty and the university hospital. In 1991 the Lund University Medical Laser Centre had been formed and over the years the cross-disciplinary work on medical diagnostics has generated several spin-off companies. The UOT project has initially partly been pursued together with an earlier spin-off company SpectraCure AB, but recently a new spin-off company Deep Light Vision has been formed for developing the UOT technique. UOT has the potential to provide optical images down to several centimetres of depth in tissue. It is in particular focused on developing the ability to measure tissue oxygenation at large depths, but might also be used for e.g. breast cancer screening.