Northumbria Optical Coatings Ltd

About Our Products

We supply a wide range of optical filters for the infrared region of the spectrum. These filters are normally combinations of thin film interference filters which can be tailor made to any wavelength, and absorption filters, which depend on the fundamental optical properties of materials.

The thin film filters comprise of stacks of thin layers (of different optical materials) in controlled thicknesses. Light is reflected at each film interface and by correct choice of parameters can be made to interfere with that from other interfaces, constructively, for certain wavelengths giving high reflectance and destructively for others, giving high transmittance. Longwave pass, shortwave pass and bandpass filters can be designed and manufactured in this way. Normally, because of the finer number of layers involved, ideal performance is obtained only over a limited range of wavelengths.

Outside this range, spurious transmission occurs and usually auxiliary filters are used to suppress the unwanted sidebands. The auxiliary filters are in most cases absorption filters, which have extensive rejection bands but which lack the flexibility of thin film filters, although sometimes additional inference filters may be used, particularly when no suitable absorption filters exist.

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