![]() ![]() A camera mirror is required in an actual monochromator, however, as light is incident over the entire surface of the dispersive element. 3 a simple exit slit can extract the required wavelength, as the light beam incident on the dispersive element is narrow. The basic elements of a monochromator are (1) entrance slit, (2) collimating mirror (to form a parallel beam after the slit), (3) diffraction grating (dispersive element), (4) camera mirror (focuses light from the dispersive element onto the exit slit), and (5) exit slit (see Fig. This wavelength is known as the "blaze wavelength." The diffraction grating in a spectrophotometer is normally used near the blaze wavelength.įig.10 Basic Elements of a Monochromator (Czerny-Turner Grating Monochromator) However, the diffracted light energy from a diffraction grating with a fine sawtooth profile is concentrated in the direction of the specular reflection, as shown in Fig. ![]() The various light orders of a diffraction grating result in dispersion of the energy and a reduction in light utilization efficiency. This is reflected as white light, equivalent to normal specular reflection. Incidentally, the light when m=0 is known as zero-order light, for which the diffraction angle θ is equal to the angle of incidence i. These light directions are named using a combination of the m value and the + or - sign, such as +1st-order light or -1st-order light. This indicates that light of wavelength λ diffracts in multiple angles θ, as shown in Fig. If d, i, and λ are fixed in expression (1), a different value of m results in a different value of θ. Modern diffraction gratings achieve comparatively low stray light.)Įxpression (1) indicates the presence of higher-order light. High (Dispersion due to higher-order light and surface roughness. Yes (Requires higher-order light cutout filter.) ![]() High (Effects of temperature on refractive index.) High for UV low for visible to NIR light. High efficiency near the blaze wavelength.) Low (Light with the same wavelength is dispersed in several directions as higher-order light. A single prism covers the range from 185 to 2500 nm.) High (Generally has high efficiency despite light losses from boundary reflection and absorption during transmission through the material. Exploits differences in the material refractive index according to the wavelength.Įxploits diffraction from a reflective surface with a regular grating structure. ![]()
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