You should see a kaleidoscope of changing colors. A fun experiment is to cover a piece of glass with many layers of overlapping clear tape going in all directions and look at the glass with polarized glasses against the light of a computer screen. ![]() Placing the tape over an empty gap in some kind of a frame also works. Then cut to remove the triangle in the middle and then place another piece of tape perpendicular to the slide so the two edges of tape meet in the middle. First, I cover more than half of the slide with tape at a 45-degree angle. I like to use a microscope slide as a support for the tape. They are orthogonal at 90 degrees but 45 degrees appears to work best. ![]() Circular polarizers are quarter-wave so they first become orthogonal at 45 degrees rather than 90 degrees as with linear polarizers. They simply give the light a “twist” as it passes through. Circular polarizers should be perfectly clear since they don’t block light the way linear polarizers do. A polarizer labeled “circular” may not be circular only so that is another thing to watch for. I have a “circular” polarizer for photographic work but it is also a linear polarizer. By rotating the glass you should see the tape go from clear to dark blue and almost black. The tape can also be applied directly to a computer screen but this could damage the screen. The easiest way to test for polarization is to apply the tape to a convenient size piece of window glass (glass from picture frames works nicely) and then observe the tape through a polarizing filter or polarized glasses against the lighted background of a flat-screen LCD monitor. Some are better than others and some hardly work at all so it helps to test them first. I find that most sources of clear tape work as polarizers. The wide packing tape works best because of its width. For my experiments, I use ordinary clear cellophane tape “Scotch tape” as a circular polarizing filter. My results so far suggest that the interference remains which favors the old Fresnel-Arago explanation over that of Skully-Druhl which has become the preferred explanation in quantum physics. My modification of the usual double-slit quantum eraser experiment is to replace the linear polarizers with circular polarizers to see if the interference pattern remains or not. I was wondering if anyone was interested in repeating the experiment to see if it confirms my results or if anyone can explain what I am doing wrong? All I could find is two anecdotal reports that circular polarizers destroy interference the same as linear polarizers. I searched the literature to see if anyone has tried the double slit experiment with circular polarizers and found nothing. I found that the two beams of light when marked with circularly polarized light provide which-path information without destroying interference contrary to the results predicted by Skully and Druhl. Circularly polarized light does not interfere destructively the way linearly polarized light does. I decided to test the Skully and Druhl hypothesis by substituting circular polarizing films for the linear polarizers in the double slit experiment. But their explanation seems dubious to me since it involves the availability of information to the observer rather than any physical interaction. The Skully and Druhl hypothesis has since become the choice of explanations for how the double slit experiment works. By marking the two beams of light with polarizing filters, which-path information is available to observers therefore the interference pattern is lost. If it is possible to determine which path the light took when going through the double slits, the interference is lost, but if the which-path information is unavailable or destroyed, the interference returns. The loss of interference was later explained by Skully and Druhl in 1982 as a matter of which-path information. Their explanation was that the two orthogonal beams of polarized light interfered so rapidly and randomly that the light became incoherent and interference became impossible to detect. The loss of interference was explained two centuries ago by Fresnel and Arago. ![]() Demonstrations of the DIY double-slit quantum-eraser can be found on YouTube for those not familiar with the experiment.The experiment demonstrates that two beams of orthogonally polarized light do not produce an interference pattern although they do produce a diffraction pattern with the double slit experiment.
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