Imagine being able to watch an embryo growing inside an egg, or examine the deep tissues in a sick patient without breaking the skin, or even see through fog and clouds directly into space.
The Ultra Fast Optics Group at the Weizmann Institute of Science in Israel have taken a huge step towards doing just that. Yaron Silberberg, the principal investigator in the team, who have published their research in Nature, says, “The main implications are that imaging through scattering [opaque] layers can be done in real-time with standard light sources and standard cameras.”
Imaging the unknown
When light encounters a surface that appears opaque it is scattered in all directions, and we can see neither what is beyond that surface nor a mirrored reflection.
Until now, if scientists wanted to create an image of what was beyond such a layer they have used either monochromatic or short-pulsed lasers to gather data and then reconstructed the image with computerised raster (line-by-line) scanning afterwards.
The research team have changed that, “Our main novel finding is that standard incoherent light (such as white light lamps and fluorescent probes) can be used for imaging through scattering media.”
Silberberg said, “Our work has shown that it is possible to use the incoherent diffuse back-scattered light, such as regular white light scattered from a wall, for imaging.”
Reconstructing scattered light
Silberberg and his colleagues have found that using a computer controlled pixilated LCD screen they can shape the wavefront of scattered light and re-form it into the original image. This can be done by correcting the scattering effect of the rough surface using a spacial-light modulator, and hence turning the surface from a ‘wall’ into a ‘mirror’.
“In a preliminary demonstration we have been able to image a distant object just by recording the light reflected from a piece of regular white paper,” Silberberg explained. “This is analogous to seeing your own reflection from a piece of white sheet paper.”
He continued, “We have also demonstrated that the same technique can be used to see through thin scattering layers, such as the [frosted glass] found in shower windows.”
Shedding light on new areas
Using a white light source in the system and real-time imaging has simplified the process dramatically and made it far more suited to practical applications.
Silberberg said, “Our technique for imaging through scattering layers may allow that study of previously inaccessible biological samples by optical imaging, e.g. imaging through thin egg shells for studying embryonic development.”
The paper discusses how valuable this technology would be in advancing progress in a broad range of scientific fields. These range from minimizing problems caused by our turbulent atmosphere during astronomical observations to microscopic imaging of tissue samples.
Derryck Reid, Head of the Ultra-Fast Optics Group at Heriot- Watt University, Scotland, who was not involved in the study commented, “Certainly this is an interesting paper, with the main power of the technique being that it can work with incoherent light.”
Like “seeing your own reflection from a piece of white paper”
Reid continued, “To become a general technique the authors will need to find a way of implementing wide field correction, rather than just local correction in the vicinity of the point source as they do at present.”
Silberberg is already hoping to do just that, he said “A major step forward would be a scheme to quickly determine the scattering properties of the medium, for example, from a photo of it.” In their current set up a calibration step is required similar to those used in adaptive optics, which correct for known turbulence or scatter.
He concluded, “The perhaps counter-intuitive result of imaging using scattered light from diffuse surfaces (such as “walls”), surprised us and captured our imagination. For us, it is as surprising as seeing your own reflection from a piece of white paper.”