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. Typically, the cost of producing a master diffraction grating is expensive and by supplying replica gratings (which offer almost indistinguishable performance), one master may produce thousands of replicas, lowering the unit cost of the diffraction grating.Exploits differences in the material refractive index according to the wavelength.Įxploits diffraction from a reflective surface with a regular grating structure. A blazed grating has a ‘saw tooth’ profile and normally offers higher efficiency.Ī commercial diffraction grating is generally a replica grating produced from a sub-master, which may be a number of generations down from the master diffraction grating. A sinusoidal grating generally offers lower efficiency than a blazed grating, but often gives a broader spectral coverage. Transmission gratings are usually supplied with an antireflection coating.Ī diffraction grating can have a sinusoidal or blazed profile. Reflection gratings are normally coated with a reflective coating, usually aluminum with a protective overcoat for UV-VIS-NIR use or gold for IR use. The most common type of diffraction grating are plane gratings and concave gratings although they can also be other profiles such as convex or toroidal depending on the application. There are typically two different types of diffraction grating – the ruled grating and the holographic grating.Ī ruled diffraction grating is produced by a ruling engine that cuts grooves into the coating on the grating substrate (typically glass coated with a thin reflective layer) using a diamond tipped tool.Ī holographic diffraction grating is produced using interference lithography which results in a smooth groove surface and eliminates the periodic errors found in ruled gratings.Ī diffraction grating can be a reflection grating or a transmission grating. The groove density, depth and profile of a diffraction grating dictate the spectral range, efficiency, resolution and performance of the diffraction grating. A diffraction grating is an optical element that diffracts energy into its constituent wavelengths.
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