In optics, a diffraction grating is an optical component with a periodic structure that diffracts light into several beams travelling in different directions (i.e., different diffraction angles). The horizontal axis represents the ratio of the wavelength λ to the grating period d, i.e., λ/ d.įor larger blaze angles (grooves depth for sinusoidal gratings), scalar theory becomes less applicable and the diffraction efficiency varies greatly with the polarization.An incandescent light bulb viewed through a diffractive effects filter. 4 shows the results of calculating the diffraction efficiency in the Littrow configuration for different polarizations. With P-polarization (TE waves), where the direction of the grating grooves and the oscillation direction of electric field vectors is parallel, there is not as much fluctuation as with Spolarization, and the diffraction efficiency describe a smooth curve that peaks at the blaze wavelength.įig. With S-polarization (TM waves), where the direction of the grating grooves and the oscillation direction of electric field vectors is perpendicular, large fluctuations in the diffraction efficiency can be observed.Īlso, a high diffraction efficiency is exhibited for long-wavelength regions. Relationship between Diffraction Efficiency and Polarizationīecause the grooves in a grating are all etched in one direction, the diffraction efficiency can vary significantly with the polarization of incident light. The values given in catalogs correspond to λ B(Litt) for plane gratings and λ B for concave gratings. Shimadzu adopts the relative diffraction efficiency. In general, there are two ways of expressing the diffraction efficiency, "absolute diffraction efficiency" and "relative diffraction efficiency." The absolute diffraction efficiency is the ratio of the diffracted light intensity, of a given order, to the incident light intensity, and the relative diffraction efficiency is obtained by dividing the absolute diffraction efficiency by the reflectance of the coating material. The diffraction efficiency is a value that expresses the extent to which energy can be obtained from diffracted light with respect to the energy of the incident light. It is also possible to deal with overlapping by changing detectors.
For example, when using first-order light with wavelengths in the range 350 to 800 nm, a filter is used to cut the overlapping second-order light with wavelengths in the range 350 nm to 400 nm, in other words, to cut light with wavelengths of 400 nm or less.
#WAVELENGTH FROM GRATING AND DIFFRACTION ANGLE FORMULA FREE#
If the applied wavelength region is wider than the free spectral range, spectra corresponding to the unrequired orders must be removed from the overlapping region. As briefly described in the section on grating equations, however, it is necessary to use an appropriate groove density for light of wavelength λ 2 at long-wavelength side, in this case 700 nm, to be obtained as diffracted one. When using second-order light, the free spectral range is from 350 to 525 nm. The range 350 to 700 nm is the free spectral range.
For example, when using first-order light with wavelengths greater than or equal to 350 nm, wavelengths up to 700 nm can be used without overlapping.
0 kommentar(er)
