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17 Jun 2002
Laser spectroscopy that analyzes murky liquids is set to make life easier for paint manufacturers.
A crucial part of paint production is to get the right particle size and distribution. However, current optical techniques such as photon correlation spectroscopy or dynamic light scattering sometimes incorrectly analyze opaque substances. This leaves manufacturers with a paint that is too viscous or won't stick to walls. But Lisa Aberle and Malte Kleemeier from Germany's Fraunhofer Institute for Materials Research are exploiting a technique called 3D cross-correlation spectroscopy, which they think will solve these problems.
The cross-correlation technique is based on angling two coherent lasers at a substance so that they cross when passed through it. The scattered light from each beam is captured by detectors that cross-correlate any spatial and temporal differences between the scattered light patterns. By repeating these measurements the researchers can track particle changes during production behavior such as aggregate growth and sedimentation.
According to Aberle the key to the technique is the position of the laser beams and detectors. "Conventional correlation spectroscopy only works reliably when the laser beam is scattered at one particle in the sample," she said. "Of course this [scenario] is only guaranteed in near-transparent systems."
But Aberle claims that by aligning the lasers and detectors to optimize cross-correlation calculations, the technique can filter scattered light that stems from just one particle, even in the murkiest of substances.
"This means mistakes [during particle analysis] are not possible," adds Aberle. "As long as you can measure the cross-correlation function, you are sure to get reliable results."
The researchers are now preparing to patent a "table-top" version of this technique for industrial applications. "We are already in contact with manufacturers," said Aberle. "I think producing this instrument commercially will be really great."
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