ABSTRACT
An optical filter is required for defining the wavelength range of the light incident upon an object, which includes the entrance slit of an optical system. There are several types of optical filters: colored glass filters, dielectric filters, neutral density filters, and Raman filters. Colored glass filters are manufactured using different types of Schott color glass. Bandpass and longpass colored glass filters for Ultraviolet, Visible, and Infrared wavelengths are commercially available from several vendors including Edmund Optics, Newport, Schott, and Thorlabs. The cut-on wavelength of a longpass filter denotes the wavelength at which the transmittance increases to 50%. Dielectric filters are fabricated by the deposition of dielectric films on substrates, which are transparent to the wavelength region of interest. Raman filters are used to suppress the pump laser line in Raman spectroscopy. Raman filters are either longpass or shortpass filters with sharp turn-on or turn-off.
