Traditional Coated Bandpass Interference Filters are used to selectively transmit a narrow range of wavelengths while blocking all others, and are ideal for a range of biomedical and quantitative chemical applications.
Bandpass interference filters are widely used in instrumentation for a variety of applications including clinical chemistry, environmental testing, colorimetry, elemental and laser line separation, flame photometry, fluorescence and immunoassays. In addition, bandpass interference filters are used to select discrete spectral lines from arc or gas discharge lamps, and to isolate a particular line from Ar, Kr, Nd:YAG, and other lasers. They are often used in conjunction with laser diode modules and LEDs.
Traditional coated filters are fabricated in three sections, one of which determines the center wavelength (CWL), bandwidth (FWHM), and the shape of the transmittance curve while the other two control the blocking range of the filter. The bandpass section of Traditional Coated Bandpass Interference Filters is made by repetitive vacuum deposition of thin layers of partially reflecting dielectric compounds on a glass substrate. Rejection of wavelengths resulting from destructive interference is limited to within 15% of the central wavelength, therefore, additional glass or metallic blockers must be added to reduce out-of-band transmittance. Metallic blockers, such as layers of silver, reflect and absorb radiation outside of the filter passband and negate higher order passbands from X-ray to the long-wave infrared (LWIR). The blocking capabilities of metallic blockers are augmented by the addition of color transmitting glass and custom dyes that absorb UV or long wavelength radiation. After thin film deposition is complete, the three sections are scribed, laminated, cut, and mounted.