Holographic Notch and SuperNotch® Filters
In 1990 Kaiser first introduced their Holographic Notch filter. The introduction of the holographic notch filter during the early 1990’s, the charge coupled-device (CCD) array detector, and the availability of compact laser are credited, by many sources, as revolutionizing the field of Raman spectroscopy.
Kaiser's Holographic Notch and SuperNotch® Filters are fabricated by recording interference patterns formed between two mutually coherent laser beams. These interference patterns are exposed and developed in a thick gelatinous film that typically is sandwiched between two glass substrates. Since all layers are recorded simultaneously within a thick stack, the optical density of the notch filter is high and the spectral bandwidth of the notch can be extremely narrow. Also, since the layering profile is sinusoidal instead of squarewave, holographic notch filters are free from extraneous reflection bands and provide significantly higher laser damage thresholds than standard interference filters.
The Holographic Notch filter and the enhanced Holographic Notch filter, the SuperNotch® filter, introduced in 1992 by Kaiser, are the standard filtering technology found in the majority of Raman spectrometers manufactured commercially and built by researchers currently. Our holographic filters can provide up to six order of magnitude of attenuation of the Rayleigh line along with sharp spectral cutoff’s that allow bands as close as 100 cm-1 to be detected.