Long Wave Pass filters (also referred to as edge filters) are constructed from stacks of thin layers. They are distinguished by a sharp transition from a zone of rejection to a zone of transmission. The rejection region extends to below 0.3um and the transmission region typically extends to greater than twice the wavelength of the edge position.
When ordering it is necessary to specify the required 5% or 50% cut on edge position (the 5% point is measured as an absolute value but the 50% point is measured as 50% of peak transmittance).
Typical Characteristics of Long Wave Pass Filters
|Available wavelength range (edge position)||~1 to 20um|
To customers requirements, from +/-1% but standard tolerance +/-4%
|Average transmittance||Typically >75% (depending on wavelength)|
|Cut on slope||Typically < 5%|
|Blocking (attenuation)||Typically <0.1% to 0.3 micron|
Northumbria Optical Coatings Ltd (NOC) was established in 1995, specializing in the design and manufacture of Infrared Optical Filters and Coatings, covering the spectral range 1.5μm – 20.0μm. Before 1995 NOC operated as a business unit for Rolls Royce International Research & Development based in Newcastle upon Tyne. NOC offers competitively priced standard and non-standard filters which are used in many applications including environmental monitoring, analysis and control of gaseous effluent, analysis of vehicle exhaust gases, ozone layer monitoring, night vision systems and space applications. Contact EOC for more information.