Linear variable filters
Edmund Optics has introduced new linear variable filters, ideal for fluorescence applications. These filters are designed for both individual and combined use for maximum versatility and are available in both long-pass and short-pass options.
Linear variable filters are manufactured with an interference coating that is intentionally wedged in one direction, creating a linear shift of the centre wavelength across the length of the entire substrate. This linear shift allows the broad filtering capabilities that are demonstrated by the shortwave and longwave variable filters.
The two types of filters – short- and longwave – work inversely to one another. The shortwave filter passes light throughout the filter's length until a blocking band is reached, while the longwave filter blocks light until a transmission band is reached. These blocking and transmission bands may be adjusted by reorienting the filter to the light source. Using its broad blocking and transmission range, a single linear variable filter can replace an entire filter set, making them extremely economical and saving valuable space.
The filters allow for blocking and passing of targeted wavelengths. When used independently, the shortwave pass filter has a wavelength range of 330-750nm with an excellent average transmission of 97 per cent from 400-750nm. The longwave pass filter has a wavelength range of 300-845nm and an average transmission of 97 per cent across its entire wavelength range for maximum efficiency. The filters provide blocking of OD>4. When the both filters are combined, they can operate as a laser-line filter or as a variable bandpass filter with a tuneable centre wavelength and bandwidth for a vast array of applications.
In order to reduce scattered light and harmonics, combined long- and shortwave filters may be synchronised with a single moving grade spectrometer. Combined linear variable filters can also be used as a single variable excitation filter for a wide variety of fluorescence applications using white light sources.