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Young's Slits - Page 8 of 8


A typical double slit result should look something like this:

The above graph, is of a set of results from mask 1, using the red laser. The sensitivity of the PMT is not constant across the window, which leads to some distortion of the diffraction pattern. There is also a lack of contrast due to the width of the acceptance slit. This is worse with the blue laser due to the fringes being closer together. Even so, the side peaks of the single slit envelope are clearly visible. The overall envelope is associated with the width of a single slit. The fine cosine structure is associated with the distance between the two slits.

I set a couple of challenges for you. Here are the answers: The wavelength of the red laser is 650nm according to the label. Actually I suspect it is nearer 620nm. The slit separation on mask 4 is 0.125mm. Well done if you got them about right.

There is a Log File that lists experiment activity since the last server restart. The columns are as follows:
The 'S' column is an internal update indicator.
The 'U' column is an internal usage code.
The 'R' column is the status of the red laser (R=on r=off).
The 'B' column is the blue laser status (B=on b=off).
The 'M' column is the selected mask.
The 'AA' column is the acceptance slit position.
The 'DD' column is the discriminator level.
The 'RRRRRRR' column is the count rate.


References for Further Study

These references are not intended to be conclusive. These are just some of the things I have read / watched'.

'In Search of Schrodingers Cat', John Gribbin.
'Quantum Reality: Beyond the New Physics', Nick Herbert.
'Quantum Physics: Illusion or Reality?', Alistair Rae.
'The Ghost in the Atom', P Davies, Julian Brown.
'The Feynman Lectures on Physics: Definitive and Extended Edition', Richard Feynman.

Online Lectures:
Prof. Walter Lewin - MIT Lecture
Richard Feynman - The Douglas Robb Memorial Lectures
Three Lectures by Hans Bethe

Single Photon Interference Experiments:
TeachSpin's Two Slit Single Photon Interference Instrument
Harvard Double Slit Single Photon Interference Demonstration

Page Title Description
Background Introduction to diffraction and Young's slits.
Information Encoding This page attempts to show the similarities between the frequency content of an electrical waveform and the diffraction pattern of an object.
Project Construction Information about how the experiment was built.
Single Photon Justification Mathematical justification that the experiment can be considered to be diffracting individual photons.
Quiz A multiple choice quiz (requires Java).
Instructions Instructions for operation of the experiment.
Online Experiment The live interactive Young's slits experiment. Please read the instructions first.

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