Document Type
Course
Journal/Book Title/Conference
Physics 3710 – Introductory Modern Physics
Publication Date
8-23-2017
First Page
1
Last Page
7
Abstract
The double slit experiment in dim light – photons!
Let’s imagine doing the double slit experiment again, but now in very dim light. To do so requires putting the laser, plate, and collector in a sealed, light-tight box. Inserting neutral density filters in the beam between the laser and the double slit plate decreases the intensity of the beam striking the plate. In fact, the experiment can be done at such a low intensity that a human eye will not see any light on the CCD collector; but the CCD can. Under these conditions, the number of pixels that “light up” during the collection time Δt is small and very rarely do two adjacent pixels light up at the same time no matter how small the pixels are (actually, the smallest pixel size achieved to date for detecting light is about 10 µm by 10 µm, and about 1 µm thick and involve trillions of atoms). In other words, the lighting of a pixel seems to be as if it is hit by a tiny particle. The sequence of hits, in dim light, is irregular. An example is shown to the right at the top. Every time the process is repeated we observe a different sequence of hit pixels. It appears to be impossible to predict what the sequence will be before it is generated. On the other hand, if this process is repeated numerous times and the hit pixels are superimposed, a regular accumulated image begins to emerge like that in the middle to the right. When such a time-lapse image is compared with the expected intensity distribution for bright light (bottom right), it is clear that the pixel hits are gradually filling in the classical interference pattern. Thus, though the hits appear to occur at random, not any thing can happen: there are constraints to the randomness. In particular, there are pixels that are more likely to be hit than others and some pixels (almost) never get hit.
Recommended Citation
Peak, David, "Foundations, 2" (2017). Foundations. Paper 2.
https://digitalcommons.usu.edu/intro_modernphysics_foundations/2