![]() This explains why some symmetric holographic gratings can achieve greater than 50% absolute efficiency in a given order, although most do not. Most holographic grating masters are generated initially with a symmetric groove profile. It is important to note that a symmetric profile holographic diffraction grating will only have symmetry in efficiency on either side of zero order when the light is incident at 0 degrees (normal incidence). Blazing is not as easy with holographic gratings however, and with certain notable exceptions, they will not be as efficient as ruled, blazed gratings. Holographic master gratings generally exhibit better stray light properties than ruled master gratings. The addition of a reflective overcoat completes the process. After development, the sinusoidal variation in light intensity during exposure is transformed into a physical structure of the same profile. The resulting interference pattern differentially exposes the photoresist. Holographic master gratings are produced by exposing a thin layer of photoresist to 2 intersecting coherent, monochromatic beams. ![]() The resulting profile will show some peak round-off, and not achieve theoretical depth. Actual groove depth is typically 90% of theoretical. As a result, there is some displacement and deformation of the material on the short facet into the previously ruled groove every time a new groove is formed. Rather, the coating is burnished by the tool. When a master ruled grating is generated, the diamond tool does not actually remove material and cut a theoretically shaped groove. The calculated theoretical groove depth is given as: Theoretical Profile of a Ruled Blazed Grating Because of the mechanical nature of the mastering process however, there can be random and periodic spacing errors that could detract from the purity of the diffracted spectra. Ruled blazed gratings are very efficient, and are generally the best choice for applications requiring high signal strength. The resulting groove profile has a well defined and controllable groove profile that directs energy efficiently into the desired wavelength range. The master gratings are produced by forming the surface of a soft metallic coating with a diamond form tool. Types of Diffraction Gratings Ruled, Blazed Diffraction Gratings Every wavelength undergoes a different phase shift, and as a result, diffracts at a different angle, resulting in a dispersion of broadband light. This redirection (or diffraction) is a result of the phase change of the electromagnetic wave as it encounters the regular, fixed structure of the grating surface. This process is experimental and the keywords may be updated as the learning algorithm improves.A diffraction grating is a passive optical component that redirects light incident upon the surface at an angle that is unique for every wavelength in a given order. These keywords were added by machine and not by the authors. Monochromators are important for color measurement because many color-related optical characteristics are dependent on wavelength. A monochromator combined with optical detectors can be used to obtain the spectral power distribution (SPD) of light sources, reflectance or transmittance of objects, etc. ![]() Monochromators are included in many optical measurement instruments and systems for applications where tunable monochromatic light is required. Although lasers produce light that is much more monochromatic than the optical monochromators discussed here, only some lasers are easily tunable but are not as simple to use. Ideally, a monochromator should produce a single wavelength of optical radiation at its output. ![]() The Greek roots “mono-” and “chroma-” refer to “single” and “color” respectively. A monochromator is an optical dispersing device that is used to select a narrow band of light (i.e., optical radiation) from a wider range of wavelengths available at the input.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |