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Plug-and-play lens brings adaptive optics to commercial platforms

30 Jun 2020

Group including Delft University of Technology simplifies adoption of adaptive techniques.

Research at Delft University of Technology alongside Italy's CNR-IFN research institute and the University of Modena and Reggio Emilia has lead to an adaptive optics module suitable for use on commercial scanning fluorescence microscopy platforms.

Reported in Optics Letters, the device is designed to be mounted on a microscope objective, adding adaptive optics correction to any microscopy platform that employs interchangeable objectives.

"Improving the technology available to life scientists can further our understanding of biology, which will in turn lead to better drugs and therapies available to doctors," said Paolo Pozzi from the University of Modena and Reggio Emilia.

Adaptive optics techniques can correct the optical aberrations that occur when imaging through thick tissue, but this often requires a custom microscope accommodating a deformable mirror, along with bespoke computational methods to control the process.

"Including a deformable mirror in an existing microscope is nearly impossible, and no commercial adaptive microscope is available on the market," said Pozzi. "This means that the only option for a life-scientist to use adaptive optics is to build the entire microscope from scratch, an operation which is too difficult and time consuming for most laboratories."

The project tackled the problem by creating a a multiactuator adaptive lens between the microscope body and the objective lens. A disk-shaped container within the adaptive lens is filled with a transparent liquid, and a set of 18 mechanical actuators on the glass edges bend the lens to a desired shape, applying a deliberate corrective distortion to the light traveling through it. As a result the lens functions in an analogous fashion to a deformable mirror, but transmitting light rather than reflecting it.

"Efficient optical correction was made possible by the DONE algorithm, or 'database online nonlinear extremumseeker,' a very elegant solution based on machine learning principles which we previously developed at TU Delft,” said Pozzi.

Image deeper under the surface

Other earlier work by Paolo Pozzi in the field of adaptive optics includes the 2018 development of a universal sensorless adaptive method, reported in PLOS One, that used a sample-independent precalibration to establish the direct relation between the image quality and the aberration. This was designed to be applicable to any form of microscopy employing epifluorescence detection, with minor hardware modifications.

Prior to that Pozzi was one of the Startup Challenge semi-finalists at SPIE Photonics West in 2016, for work on a holographic module allowing conversion of standard microscopes into multiphoton spatial light modulation microscopes.

In trials, the new adaptive objective was tested on both a commercial linear excitation confocal microscope and a custom-made multiphoton excitation microscope. Calcium imaging was carried out on the brains of living mice, and the researchers said that they were able to generate corrected images within a few hours. Future work will now include testing the system on other types of microscopes and samples, and an investigation into whether multiple adaptive lenses can achieve a better correction than more complex techniques using deformable mirrors.

The technology is now set to be exploited commercially by Dynamic Optics, a Padua-based spin-out specializing in light control technology, and which is already a developer of adaptive lenses, deformable mirrors and wavefront sensors.

"This approach will allow advanced optical techniques such as multiphoton microscopy to image deeper under the surface of the brain in live organisms," said team member Stefano Bonora of CNR-IFN. "We look forward to seeing how it might also be implemented in other systems, such as light-sheet microscopes, super-resolution systems, or even simple epifluorescence microscopes."

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