Diffraction gratings for spectral devices [Review]

Subject of study. This review is intended to acquaint the reader with various types of diffraction gratings and technologies for fabricating them. Method. An information search on the topic, systematization, and analysis are performed. Main results. This paper briefly discusses the areas of application and classification of spectral devices and shows the variety of problems that can be solved by means of spectral devices and that impose various requirements on diffraction gratings. It lists the main characteristics of diffraction gratings used in spectral devices and specifies the stages of their improvement. It discusses classical reflective diffraction gratings—plane (profiled and laminar) and concave. It describes the principles involved in obtaining holographic diffraction gratings and their advantages over ruled ones. It devotes special attention to concave holographic gratings with aberration correction, shows how they are classified, and briefly describes methods of optimizing the parameters of gratings that operate in monochromator systems with simple rotation and flat-field spectrographs with correction of defocusing, astigmatism, and meridional coma, as well as various methods of recording gratings in nonhomocentric beams to expand their correction possibilities. Ruled analogs of holographic gratings are used in a number of cases. It is pointed out that foreign and Russian firms that batch-produce diffraction gratings of the types described here completely satisfy the requirements of the batch-producers of spectral devices. The features of using volume phase gratings in spectral devices are considered, and it is pointed out that, even though these gratings are distinguished by high efficiency, their angular and spectral selectivity have inhibited these gratings from being widely applied in spectral devices. However, there have been active studies in recent years on expanding the regions in which volume phase gratings are used: new system solutions, recording materials, and recording methods have been proposed. Trends to create diffraction elements that combine various functions (cross gratings and grisms) are pointed out. New technologies are proposed for fabricating diffraction gratings: ruled gratings—pendulum-type ruling engines, gratings that reflect with high diffraction efficiency in an expanded wavelength range—“efficiency-achromatization” or double-blaze technologies and volume phase gratings—ultrafast laser inscription and profiled diffraction gratings that operate in the x-ray region—electron-beam lithography, to miniature spectral devices—microelectronic mechanical systems technology used in electronics, composites—concepts of a composite volume phase diffraction grating recorded by integrating several elementary fields. The Conclusion evaluates the modern level and points out development trends. Practical significance. The material presented here can be useful in the development of spectral apparatus.