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Narrow bandpass filters are designed to isolate a narrow region of the infra-red spectrum. This is accomplished using a complex process of constructive and destructive interference. Narrow band pass filters have bandwidths (measured at half-peak transmittance levels) less than 6% of the centre of wavelength value. When ordering, the bandwidth can be expressed as a percentage of the centre wavelength, or can be given in microns. The filters exhibit high peak transmission (typically greater than 60%) combined with high attenuation levels outside the passband (typically less than 0.1%).
Typical Performance

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Typical Characteristics
| Available wavelength range |
~2 to 20um |
| Tolerance on CWL |
To customers requirements, but standard tolerances are typically +/-0.3% for a 1% bandwidth filter to +/-1% for a 6% bandwidth filter |
| Peak transmittance |
Typically >60% (depending on wavelength and bandwidth) |
| Available bandwidths |
Typically 0.9% to 6% |
| Blocking (attenuation) |
Typically <0.1 % from 0.3 micron to far infrared |
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