Fluorescence sizes up coatings

15 Oct 2003

A fluorescence detection technique promises precise in-line measurement of coatings.

New fluorescence-based metrology equipment looks set to simplify the challenge of measuring optical coatings that are just a few nanometers thick.

The ScalarGauge F system from the Scottish start-up Scalar Technologies uses laser technology to determine the thickness of a thin coating that has been applied to a plastic film. Potential applications include analysis of anti-reflection or anti-glare coatings, adhesives or ink-primers.

Scalar says that system, which will be unveiled at next month’s International Converting Exhibition in Munich, can measure coatings between 1 nm and several micrometers thick that are moving at high speeds in a manufacturing facility.

“The system has been used with web speeds measured at 300 meters per minute and there’s no reason why we can’t go faster,” commented Steve Tomlinson, Scalar’s sales and marketing director. “To the best of our knowledge there are no other means for in-line measurement of sub-micron coatings.”

The system works by adding trace quantities of a fluorophore called ScalarAdd into the coating mixture before it is applied to the film. After deposition, a green diode-pumped Nd:YAG laser illuminates the film, exciting the fluorophores in the coating and generating red fluorescence which is captured by a detector. The strength of this light emission directly relates to the coating’s thickness, the brighter the fluorescence the thicker the film.

According to Tomlinson, the use of such tiny quantities (a few parts per million) of the fluorophore means that its addition has no effect on the appearance of the coating. He also says that the approach is designed for solvent-based coating processes as they allow the fluorophore to dissolve.

Scalar, which was founded in 1999 and is based in Livingston near Edinburgh, initially developed the technology for analyze coatings required for hot stamping foils but has since adopted it to suit other applications including optical coatings.

Author
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.