$diffraction film$

$diffraction film$

In fact, each ray from the slit interferes destructively with another ray. A ray from slightly above the center and one from slightly above the bottom also cancel one another. Thus, a ray from the center travels a distance less than the one at the bottom edge of the slit, arrives out of phase, and interferes destructively. In part (b), the ray from the bottom travels a distance of one wavelength farther than the ray from the top. However, when rays travel at an angle relative to the original direction of the beam, each ray travels a different distance to a common location, and they can arrive in or out of phase. When they travel straight ahead, as in part (a) of the figure, they remain in phase, and we observe a central maximum. (Each ray is perpendicular to the wave front of a wavelet.) Assuming the screen is very far away compared with the size of the slit, rays heading toward a common destination are nearly parallel. These are like rays that start out in phase and head in all directions. According to Huygens’s principle, every part of the wave front in the slit emits wavelets, as we discussed in The Nature of Light. We then consider light propagating onwards from different parts of the same slit. Here, the light arrives at the slit, illuminating it uniformly and is in phase across its width. The analysis of single-slit diffraction is illustrated in (Figure). (b) The diagram shows the bright central maximum, and the dimmer and thinner maxima on either side. The central maximum is six times higher than shown. (a) Monochromatic light passing through a single slit has a central maximum and many smaller and dimmer maxima on either side. For red light of wavelength 600 nm, this would give a first order diffraction maximum at about 22°. This is in the range of ordinary laboratory diffraction gratings. The nominal track separation on a CD is 1.6 micrometers, corresponding to about 625 tracks per millimeter. The tracks of a compact disc act as a diffraction grating, producing a separation of the colors of white light. The hydrogen gas in a thin glass tube is excited by an electrical discharge and the spectrum can be viewed through the grating. The illustration shows the hydrogen spectrum. It acts as a 'super prism', separating the different colors of light much more than the dispersion effect in a prism. The diffraction grating is an immensely useful tool for the separation of the spectral lines associated with atomic transitions. However, angular separation of the maxima is generally much greater because the slit spacing is so small for a diffraction grating. The condition for maximum intensity is the same as that for a double slit. The relative widths of the interference and diffraction patterns depends upon the slit separation and the width of the individual slits, so the pattern will vary based upon those values.

$diffraction film$

The overall grating intensity is given by the product of the intensity expressions for interference and diffraction. The intensities of these peaks are affected by the diffraction envelope which is determined by the width of the single slits making up the grating. There are multiple orders of the peaks associated with the interference of light through the multiple slits. This illustration is qualitative and intended mainly to show the clear separation of the wavelengths of light.

$diffraction film$

Different wavelengths are diffracted at different angles, according to the grating relationship.Ī diffraction grating is the tool of choice for separating the colors in incident light. Orders 1 and 2 are shown to each side of the direct beam. When light of a single wavelength, like the 632.8nm red light from a helium-neon laser at left, strikes a diffraction grating it is diffracted to each side in multiple orders. The peak intensities are also much higher for the grating than for the double slit. The condition for maximum intensity is the same as that for the double slit or multiple slits, but with a large number of slits the intensity maximum is very sharp and narrow, providing the high resolution for spectroscopic applications. A large number of parallel, closely spaced slits constitutes a diffraction grating. This 'super prism' aspect of the diffraction grating leads to application for measuring atomic spectra in both laboratory instruments and telescopes. When there is a need to separate light of different wavelengths with high resolution, then a diffraction grating is most often the tool of choice.

$diffraction film$

Diffraction film