When considering a grating monochromator, think of the entrance slit as a polychromatic radiation source. There are five components found in most grating monochromators: an entrance slit, a collimating lens or mirror, a reflection grating, a focusing element, and an exit slit. Grating monochromators are located within compartments of some AAS instruments and are responsible for producing narrow bands of radiation. Interference Wedge Grating Monochromators By choosing the correct position on the wedge, variable bandwidths of ~20 nm can be isolated. Interference filters only transmit certain wavelengths Ī wedge dielectric of different thicknesses can transmit a wide range of wavelengths without having to change the interference filters in an instrument. The transmitted radiation will have a very narrow bandwidth. The thickness of the dielectric and the reflectivity of the metallic films are carefully selected because these factors control the transmitted wavelengths. These filters will reflect some wavelengths of radiation while transmitting others.Īn interference filter is composed of a transparent dielectric sandwiched between two semitransparent metallic films and then two glass plates to protect the filter. Interference filters are sometimes called Fabry-Perot filters and are dependent upon the concept of wave interference. An absorption filter and a cut-off filter used in combination will only transmit their common wavelengths. Only the common wavelengths of the two filters will be transmitted which will achieve a much narrower bandwidth than absorption filters alone. Usually, cut-off filters are not used as wavelength selectors but are used in combination with absorption filters to decrease the bandwidth of the absorption filter. However, this is only achieved for a specific band of wavelengths and transmission rapidly decreases to zero over the remainder of the spectrum. With cut-off filters, the transmission of radiation is nearly 100%. Absorption filters only allow specific wavelengths to pass through Only about 10-20% of the incident radiation is transmitted through an absorption filter. They are inexpensive and can be as simple as colored glasses or plastics. They can be divided into four main categories: absorption filters, cut-off filters, interference filters, and interference wedges.Ībsorption filters absorb most polychromatic radiation and transmit only a specific band of wavelengths. Filtersįilters are wavelength selectors that allow narrow bandwidths of radiation to pass through. Here we will consider filters, grating monochromators, and prism monochromators. There are several types of wavelength selectors.

Sensitivity of an AAS is improved when the bandwidths are narrow and detectability is improved when transmission is high. Wavelength selectors limit the radiation absorbed by a sample to a certain wavelength or a narrow band of wavelengths.

Uv vis cut off wavelength