The infrared spectrum is much broader than that of the visible spectrum. The graphic in figure 1 illustrates that the spectral range of the MWIR is 6.5 times as broad as the visible, and the LWIR is 20 times as broad. Color correction is thus needed over a much larger range of wavelengths, and materials are required that cover a broader spectral band than normal glasses.
By taking into account the erratic optical dispersion, optical materials can be combined to create a single refractive lens system for imaging across the visible to long wave IR , or disparate subsections within this range.
Long Wave Pass Filters comprise single and boxed set. These filters are made using IR substrates such as silicon, sapphire, germanium, IR quartz etc. with thin films of material that have differing refractive indices and thickness to achieve very shape cut-on at required wavelength in the Infrared region. The filters are used to block the short waveband and transmit the long wavelength and therefore serve to remove any non-required wavelengths and transmit the required ones. These filters can help with reducing the noise and thus improve the signal to noise ratio. They can be used in combination with the short wave pass filters to form a band pass filter. This combination can have variable bandwidths that are tuned by the use of different long and short pass filters.
Call PFG technical sales team and discover how PFG Optics IR Long Wave Pass Optical Filters and service can improve your instrumentation.