The intensity of these spots decreases as the diffraction order increases, and the number of higher order diffracted waves that can enter the lens is restricted by the size of the lens aperture. If the diffracted light waves produced by the periodic grating are then passed through a convergent lens, they appear as a series of bright spots on the focal plane of the lens. The combination of diffraction and interference effects on the light wave passing through the periodic grating produces a diffraction spectrum, which occurs in a symmetrical pattern on both sides of the zero order direct light wave. Where λ is the wavelength of the wavefront, P is the grating slit spacing and M is an integer termed the diffraction order (e.g., M = 0 for direct light, ☑ for first order diffracted light, etc.) of light waves deviated by the grating. Diffracted higher-order wavefronts are inclined at an angle ( θ) according to the equation : Wavefronts passing through the grating slits that are parallel to the incident light wave are referred to as zero order (undiffracted) or direct light. Individual light waves diffracted from successive grating slits are emitted as concentric spherical wavelets that interfere both constructively and destructively because they are all derived from the same wavefront and are therefore in phase. The Spatial Frequency slider is utilized to change the grating periodicity and the Wavelength slider alters the wavelength of the incident light wave. Each slit in the grating diffracts light over the entire range of angles covering 180 degrees on the opposite side of the grating. The tutorial initializes with a grating periodicity of 1000 nanometers (producing a spatial frequency equal to 1000 lines/millimeter) and an incident light beam of 700 nanometer wavelength impacting the grating at a 90-degree angle. The spacing between the centers of two adjacent slits ( P) is called the grating period, and the reciprocal of P is termed the spatial frequency, which is measured in the number of slits or periods per unit length. The most convenient and accurate method of forming gratings of this type is through the use of metallic vacuum deposition techniques. In its simplest form, a line or amplitude grating is composed of a linear array of thin opaque strips (or slits) having a periodic spacing and suspended on a solid matrix, usually an optical glass plate. This interactive tutorial explores the mechanics of periodic diffraction gratings when used to interpret the Abbe theory of image formation in the optical microscope. Light passing through the grating is diffracted according to the wavelength of the incident light beam and the periodicity of the line grating. Light Diffraction Through a Periodic Grating - Java TutorialĪ model for the diffraction of visible light through a periodic grating is an excellent tool with which to address both the theoretical and practical aspects of image formation in optical microscopy.
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