This mounting is practical and necessary for laser tuning applications, but most applications will require some deviation between the incident and diffracted beams. The blaze angle of a ruled grating is calculated based on this mounting. In this mounting configuration, the diffracted order and wavelength of interest is directed back along the path of the incident light (i=i’).
This is the Littrow (or autocollimation) mounting. Because of the infinite number of configurations that a grating can be used in, a standard geometry is used in the measurement of the gratings. The efficiency curves in this brochure present absolute efficiency data.Īngle of incidence plays a role in grating performance. A relative efficiency curve will always show higher values than an absolute efficiency curve for the same grating. When comparing grating performance curves, it is important to keep this in mind. In contrast, relative efficiency compares the energy diffracted into the desired order with that of a plane mirror coated with the same material as the grating. The absolute efficiency of a grating is the percentage of incident monochromatic radiation that is diffracted into the desired order. Grating efficiency is a function of groove shape, angle of incidence and the reflectance of the coating. The general grating equation is usually written as: nλ = d(sin i + sin i’) where n is the order of diffraction, is the diffracted wavelength, d is the grating constant (the distance between successive grooves), i is the angle of incidence measured from the normal and i’ is the angle of diffraction measured from the normal.įor a specific diffracted order (n) and angle of incidence (i), different wavelengths (λ) will have different diffraction angles (i’), separating polychromatic radiation incident on the grating into its constituent wavelengths. To learn more about our ruling and holographic mastering processes, click here.
Ruled and holographic gratings differ in their optical characteristics and each type has advantages for specific applications.
CALCULATE WAVELENGTH FROM DIFFRACTION ANGLE FULL
We are one of the few companies that produce both types of gratings in-house and has full replication facilities and expertise. Gratings produced from laser constructed interference patterns and a photolithographic process are known as interference or holographic gratings. Physically forming grooves into a reflective surface with a diamond mounted on a “ruling engine” produces ruled gratings. The way in which the grooves are formed separates gratings into two basic types, holographic and ruled. If the wavelength is much smaller than the groove spacing, the facets of the groove will act as mirrors and, again, no diffraction will take place. If the wavelength of the incident radiation is much larger than the groove spacing, diffraction will not occur. The distance between adjacent grooves and the angle the grooves form with respect to the substrate influence both the dispersion and efficiency of a grating.
CALCULATE WAVELENGTH FROM DIFFRACTION ANGLE SERIES
A grating consists of a series of equally spaced parallel grooves formed in a reflective coating deposited on a suitable substrate.
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