Luckily it is now possible to buy cheap plastic diffraction gratings these are sometimes sold as sheets of material that can be used for various decorative purposes. These would be very difficult to make at home.
Transmission diffraction gratings involve a large number of very fine vertical lines. If the diffraction pattern remains unchanged when the laser is directed at different parts of the slit, it indicates that the sides of the slit are reasonably parallel. If there were no errors in setting the slit width and in measuring the diffraction pattern the points would be expected to lie exactly on the dashed line. Here's plot of the nominal slit width (it is difficult to set the slit width accurately) and the slit width calculated from the measured diffraction pattern. The slit width a was then estimated by measuring the distance y between n adjacent minima by comparison with the photograph of the ruler. The angle θ is sufficiently small so that the approximation sinθ = tanθ = θ is appropriate. Where λ denotes the wavelength and a denotes the width of the slit. The mth minimum should subtend an angle θ given by Here are some examples of the diffraction patterns I photographed. The camera and slit should then not be moved, and the focal length of the camera lens should not be adjusted. The distance L from the slit to the wall was measured and to simplify measurements an intial photograph was taken with a ruler taped to the wall. The beam from a laser pointer was pointed at the slit so it produced the diffraction pattern on a convenient wall.
For example the thickness of the top E string for an electric guitar can be 8, 9, 10, 11, 12, or 13 thousandths of an inch - approx 0.22 to 0.33 mm - depending upon the manufacturer and how they are classified (from 'extra super light' up to 'extra heavy').įor the photographs below I used a set of Feeler gauges – these are sets of very thin metal used to set mechanical tolerances precisely – a set of 30 with thicknesses ranging from about 0.04 to 0.8 mm typically costs less than $A10 in hardware or automotive shops. fine wire - if you know the relevant gauge.photocopy paper (80g/m 2 has a nominal thickness of 106 μm - the thickness is often displayed on the packet),.brass or plastic shim shim (very thin sheets of brass or plastic used to adjust mechanical clearances),.Possible thin objects to set the spacing include: If the edges are not parallel, the resulting diffraction pattern will be different for different regions of the slit. the slit has a uniform width, and that the spacing is the same as the width of the object used to set the spacing. I deliberately did not use a magnifier or microscope, but they can help in ensuring that the edges of the slit are parallel, i.e. Different spacings can be made by using multiple layers of an object. If sufficiently small, the object can be left in place, or otherwise carefully removed.
The spacing between the blades can be set by placing a suitable very thin object(s) between them and carefully closing them upon the object care must be taken not to cut or indent the thin object and also to keep the edges of the two blades in the same plane so they don't overlap.
The above photo was taken before the shiny surfaces were blackened with a marker pen. The two utility knife blades are clipped together with a small gap between their edges. Also beĬareful about 'specular' reflections i.e. WARNING: Never look directly at a laser pointer, or shine it at someone else. Because you will probably use a laser pointer to illuminate the slit, it is a good idea to minimise any reflection from the slit by using a black marker pen to paint any shiny surfaces so you do not accidently reflect laser light into your eye. I have used two binder or bulldog paper clips to keep the blades in position. Instead here I have used two blades from a utility knife (often called a “Stanley” knive or a boxcutter). Traditionally single razor blades were used as they were very widely available - however this is not the case in these days of multiple blade shavers. One method is to make a very small gap between two thin pieces of metal with very straight and very thin edges. However it is relatively simple to make fixed slits with suitable dimensions. It is also possible to buy adjustable slits. Commercial slides are available with a range of single slit dimensions.
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