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What Is a Blazed Grating?

Andrew Kirmayer
Andrew Kirmayer

A blazed grating is a type of diffraction grating, used in spectroscopy, with grooves shaped into right triangles to concentrate light at a specific wavelength. Light can be transmitted or reflected at a high efficiency, at the exact wavelength needed for an application. The blaze angle controls which wavelength is diffracted from the overall beam of light. When a blazed grating is integrated into optical devices, applications in chemistry, biology, telecommunications, and astronomy are benefited by the analysis of specific light wavelengths.

The wavelength the blazed grating produces depends on the blaze angle. For that specified wavelength the absolute efficiency of the separated light beam is very high, but much lower for other light wavelengths in the spectrum. Another characteristic of the grating is how it handles stray light, which is strongly influenced by how the grating is manufactured. Low stray light levels result in more efficient optical instruments and accurate scientific measurements.

Woman holding a disc
Woman holding a disc

Engineers use a blazed grating for accurate measurements of many things. Such experiments are conducted to analyze the interactions of atoms and study the characteristics of molecules in physics laboratories. The analysis of light also helps to learn about different stars located millions of light years away, or determine what substances are in the atmospheres of far away planets. Similar gratings are used in fiber optic networks to allow for more devices and people to communicate over single systems.

Astronomy is one area that the blazed grating is commonly used in. The accuracy is taken advantage of by systems such as the High Accuracy Radial velocity Planet Searcher (HARPS) echelle spectrograph in Chile, South America. It has analyzed thousands of stars and has used subtle measurements to discover planets in distant parts of the universe. As with other aspects of the blazed grating, resolution is determined mathematically. The number of grooves on the grating and their diffraction order are used in an equation to calculate resolution.

The first diffraction grating was made in the 1780s and the concept was refined in the 1800s. Blazed grating production has advanced in the 21st century to meet the demands of automated manufacturing, semiconductor processing, laser systems, and medical instruments. Automated systems are even used to control the blaze angle of the grooves. Thousands of grooves can be fit into 0.04 inches (one millimeter) of space, all with precise angles and shapes.

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