Physicists at the University of Twente (Enschede, Netherlands) have successfully focused a beam of light through an opaque medium. Normally, opaque substances such as milk or paint will only scatter light waves. But through careful sculpting of the incoming beam, processing tiny portions of the wavefront, the Dutch researchers were able to focus the beam to achieve 1000 times more intensity than normal.
The scientists sent 632.8 nm helium-neon laser light through a 10.1-µm-thick layer of rutile (titanium dioxide) pigment and recorded the attenuation of the beam at various points behind the sample using a CCD camera. From this, they calculated scattering coefficients corresponding to the degree of statistical scattering across the face of the sample. Then they used a liquid-crystal spatial phase modulator to shape the incident wavefront to match the scattering sample and correct for it. The titanium dioxide normally transmits 10% of the total light, but with the modulator in place, the transmission at the central spot was enhanced by a factor of approximately 1080, significantly improving the ability to study dispersive mediums such as single cells embedded in tissue. Contact Ivo Vellekoop at [email protected].