![]() ![]() Efficiency is determined with mercury and laser light sources to ensure narrow spectral line widths. Resolution close to the theoretical limit can be verified by interferometric and Foucault wavefront tests, and also by observation of the hyperfine spectra of mercury. ![]() Richardson's echelle gratings are subjected to careful testing. Our echelle gratings have been used in several space spectrographs, including the Hubble Space Telescope. Since they operate in many diffraction orders, echelles are capable of wide wavelength coverage, being used from 100 nm into the infrared. Common applications include atomic absorption spectroscopy, laser tuning, and astronomy. The combination of grating and dispersing element leads to the ability to focus an image on a flat plane compatible with CCD or CID detectors. Some type of order separation is essential, with cross-dispersion provided by another grating or a prism. Overlapping of diffraction orders is an important limitation of echelle gratings. ![]() They are often used in or near Littrow configuration, in which the angle of incidence equals the angle of diffraction. Providing very high dispersion and resolution, echelles enable compact system design. The virtue of an echelle lies in its high efficiency and low polarization effects over large spectral intervals. Unlike conventional ruled gratings, Echelle Gratings are coarse, high-blaze angle gratings used in high diffraction orders. Since the grooves are symmetrical, they do not have a preferred blaze direction and hence, the gratings carry no blaze arrows. We have found that three modulation levels (high, medium, and low) are adequate for nearly all purposes. The lower the modulation, the shorter the wavelength limit to which the grating can be used, but the peak efficiency may be lowered as well. Richardson Gratings offers a wide selection of holographic gratings with varying modulation depths (the ratio of groove depth to groove spacing). Like their ruled counterparts, holographic gratings are most effective when used in the Littrow configuration. Holographic gratings can provide excellent wavefront flatness and high efficiency in a single plane of polarization. They typically have a sinusoidal groove profile and are generated by the recording of an interference pattern onto a photoresist-coated substrate. Generated optically, our Plane Holographic Reflection Gratings generally do not display periodic errors or ghosts often found in ruled gratings. Utilizing a high fidelity cast replication process, developed and enhanced through years of research and manufacturing experience, we have the ability to provide duplicates of master gratings that equal the quality and performance of the master grating. Mechanically ruled, individual grooves are burnished with a diamond tool against a thin coating of evaporated metal. These ruling engines provide gratings with triangular groove profiles, very low Rowland ghosts, and high resolving power. At Richardson Gratings, we have three ruling engines in full-time operation, each producing high-quality master gratings each year. Ruled gratings are especially useful in systems requiring high resolution. Typically used in systems with collimated, incident light, plane ruled gratings require auxiliary optics, such as lenses or mirrors, to collect and focus the energy. Ruled gratings comprise the majority of diffraction gratings used in spectroscopic instrumentation. Gratings used in the Littrow configuration have the advantage of maximum efficiency (or blaze) at specific wavelengths. In Littrow use, light is diffracted from the grating back toward the source. The groove spacing and blaze angle determine the distribution of energy. Designed for first order Littrow use, Our Plane Ruled Diffraction Gratings are blazed for specific wavelengths and generally have high efficiency at those wavelengths. ![]()
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