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Filters feature variable bandpass

14 Sep 2007

Users of Schott’s latest all-purpose interference filters can choose and vary the transmission characteristics.

Applications such as analytical and environmental science, medical and biotechnology, and genetics and fluorescence measurement could all benefit from Schott’s latest interference filters. Called “Veril” filters, the product uses thin layers to either transmit or reflect various colors of the spectrum.

“Our Veril filters are “all-purpose” interference bandpass filters with a central wavelength that varies linearly over the length of the glass substrate,” Ulf Brauneck, head of coating filters at Schott told optics.org. “Depending on the position of a 1 mm slit along the filter’s base length, the characteristics will differ.”

Whereas standard interference filters only transmit and block one particular waveband, Brauneck explains that a Veril filter follows a pre-defined progression throughout its entire surface.

“The Veril filter’s central wavelength varies remarkably linearly over the length of the filter, whereas the maximum transmission and half width vary only slightly over the spectral range,” said Brauneck. “The typical long wave blocking range is twice the value of the center wavelength with an average transmittance of <=10-4 within the blocking range.”

Although Veril filters were first developed in the 1980s, Schott says that it has made significant progress in refining the wavelengths, improving processes and developing customer-specific dimensions, spectral requirements and different linear dispersions.

“Thin interference layers are applied to the substrate using the electron-beam evaporation process,” explained Brauneck. “Schott’s continual development of materials means that these layers are capable of resisting harsh environmental influences and major shifts in temperature.”

Schott manufactures both standard and customized interference filters within the spectral region of 200 to 2000 nm. However, Veril filters are standardized for the wavelength ranges 400 to 700 nm and 400 to 1000 nm. Brauneck adds that other ranges are available on request and that the vast majority of all products shipped are developed and manufactured to meet specific customer specifications.

For example, Sunrise, a microplate absorbance reader being developed by Austrian company Tecan, is just one product that uses a Veril filter. The reader is used in analytic laboratories to test blood, urine and genetic samples that have been tagged with a dye that emits at a specific visible wavelength. The bandpass characteristic of a Veril filer allows a narrow wavelength (relating to the dye) to be transmitted while the rest of the visible spectrum is blocked.

Author
Jacqueline Hewett is editor of Optics & Laser Europe magazine.

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