![]() The good news is, once a master grating meets specification, it can be used to make hundreds of thousands of replicated gratings-in reality though, a master grating is typically only replicated a few dozen times. Precision optical and metrological inspection is completed between each run. It is also an iterative process-fabricate, inspect, adjust-repeated until the target specification is met. Slight variations in groove shape, spacing, parallelism or processing can result in an out-of-spec grating. Making a master grating is a precise and laborious process that can take several weeks. ![]() The master grating is completed by grooving the surface with either a ruling engine or holographic system.īefore reliable replication methods were developed, all diffraction gratings were essentially master gratings. Photosensitive (photoresist) coating is used for holographic diffraction gratings. For ruled diffraction gratings, the surface is then coated with aluminum using vacuum deposition. Master gratings are first-run diffraction gratings where a substrate, likely glass or copper, is polished to a finish better than one-tenth of a wavelength (λ/10) with a high degree of flatness. Replication, which can produce identical diffraction gratings from a master grating, has improved repeatability, cost, and manufacturing time, making diffraction gratings more readily available for various applications. Modern ruling engines use interferometry with closed-loop control technology and environmentally controlled chambers, which add a greater level of precision and control to the master grating. Ruling engines are still widely used today alongside systems that use monochromatic and coherent lasers to produce holographic diffraction gratings. Cost, long manufacturing times, and part-to-part variation limited their application. Early diffraction gratings were made using complex, mechanical ruling engines run by expert operators in highly controlled environments. The human eye cannot discern the grooves, so inspection and metrology of diffraction gratings require technology like Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).ĭue to groove spacing and accuracy requirements, fabricating diffraction gratings is an arduous task requiring precision machines. In contrast, the average width of a human hair is 70μm. By comparison, the width of a spider’s silk is less than 4μm which is the size of each groove on a 250 grooves/mm grating. An in-depth discussion of performance characteristics can be found in our diffraction gratings knowledge base.ĭiffraction gratings often have hundreds or thousands of grooves per millimeter. When the incoming light reflects off the grooves, the resulting wavefront division creates a dispersion pattern that is characteristic of the groove spacing and incident radiation. A reflective diffraction grating has a highly reflective surface with a series of equally spaced parallel grooves. While the functional principles are similar, there are two types of diffraction gratings – reflection and transmission. Most notably, diffraction gratings are widely used in monochromators and spectrometers. The ability to precisely disperse light makes them a critical component in a variety of applications. Unlike prisms though, diffraction gratings offer dispersion that follows a sinusoidal relationship according to the grating equation. Similar to prisms, they split polychromatic light into its constituent wavelengths. Diffraction gratings are a dispersive optical component.
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