As discussed in the theory, a diffraction pattern of U(y) = Sin[y]/y (the intensity of such a pattern is |U(y)|^2) should appear on the Fraunhofer Plane. Here is a photo of such diffraction:
With no spatial filter used at the Fraunhofer Plane, the following is the image (obviously black and white) recorded by the camera (with a neutral density filter of 1000 in front of the shutter - used in all pictures of the images):
Notice that this
is not a perfect image of a slit. An exact, magnified image of the aperture should
appear in the camera. There is a loss of information due to the finite size of the
converging lens but mostly because of aberrations on the lens itself and the mirror in our
setup. Measuring the image width allowed us to determine the slit-width to be ~ 0.95
mm
The following are pictures of images formed when spatial filters are used. The first of that of when all the light is blocked excluding the central peak. The second shows the resulting image when the central peak is filtered:
Notice the image has even more
'holes' in it. When a spatial filter is used, information from the object is
lost. Therefore, not all of the image can be formed. As more of the
information is blocked, less of the complete image will appear.
The following shows the diffraction pattern with a wire screen used as the aperture:
Without a spatial filter, the image that appears at the camera's shutter looks like:
Notice that you
can see aberrations in the image - it's not a perfect image of a screen. This is for
the same reason as stated for the slit image. We measured the spacing between the
'wires' and the width of the 'wires' on the image and found, for the object, the spacing
between wires to be ~ 0.16 mm and the width of the wires to be ~ 0.036 mm. When a
spatial filter is used to remove the entire, central horizontal diffraction component, the
following image appears:
With this filter,
the image almost lacks observable horizontal 'wires.' When the horizontal pattern
was removed at the Fraunhofer Plane, it almost has the same effect that removing all the
horizontal wires in the screen would have on the image. The diffraction pattern
appears perpendicular to the orientation of the diffraction aperture.
As seen with the vertical oriented slit, the
diffraction pattern is horizontal and the image is again vertical. When the
horizontal component of the screen's diffraction pattern is removed, the pattern appears
similar to that of a slit, oriented horizontally. However, in the above picture, it
can be seen that blocking the central, horizontal component of the diffraction pattern
does not prevent all of the horizontal components from traveling to the image plane.
These components converge to form, with the vertical components, an image that
seems to be largely the result of an aperture of vertical wires.
If one compares the above image with the one formed when no spatial filter is used, it can be observed that there still, though faintly, appear lines in the horizontal direction = remnants of the horizontal wires (as seen below). These are due to the horizontal components passing the filter.
When a pinhole in a piece of aluminum foil was used as the aperture, the following diffraction pattern results:
Obviously, we were not skilled enough to make a perfectly circular aperture, but it's close enough. We measured the diameter of the image and determined the actual hole's diameter to be ~ 0.12 mm. When no spatial filter was used, the following image resulted:
We used a filter that allowed the central peak and the horizontal
information of height = the diameter of the central disk pass, but blocked the rest.
This is the result:
Obviously, there
is not much noticeable difference The right and left hand sides of the image appear
chopped off. As more of the information is removed, i.e., the width between the
filters is decreased, the image begins to appear like a vertical slit.