Physics Help Forum Layer thickness reflection

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 Feb 1st 2017, 05:25 AM #1 Junior Member   Join Date: Feb 2017 Posts: 2 Layer thickness reflection Hi, For my exam-preparation I want to solve this question: Three layers of material, with n1
Feb 1st 2017, 10:47 AM   #2

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 Originally Posted by BasWage Hi, For my exam-preparation I want to solve this question: Three layers of material, with n1
The main idea behind the cancellation we need for the wave at the interface to be at a half wavelength, so the reflected wave completely cancels...ie. the incoming wave has a node at the interface and the reflected wave is pi out of phase from the incident wave.

-Dan
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 Feb 2nd 2017, 05:13 AM #3 Junior Member   Join Date: Feb 2017 Posts: 2 Hi Dan, Thank you for your response! Yeah, I totally agree with you, I know that that is the intention of this exercise. However, as I worked it out in a drawing, it seemed that this phase shift of pi is not going to happen. But, I think I found my fault. Assuming that at the interface a phase shift of pi happens. Apparently, if a wave strikes this interface at its node (coming from a top), the reflected wave travels back in the exact same way as it came in (so going back from the node to a top). This is very counter intuitive (for me), because I thought a phase shift of pi implies that the wave gets mirrored about its neutral axis. Anyhow, I think I understand it now! Thanks again!
 Feb 6th 2017, 01:44 AM #4 Physics Team   Join Date: Feb 2009 Posts: 1,425 Since there is a phase change of pi / 2 at both surfaces, we can neglect the effect of this phase change. It is as though it didn't happen at all. For minimum intensity, the path difference has to be lambda / 2, of which lambda / 4 is covered on the first leg and lambda / 4 on the return trip. Hence the thickness should be lambda / 4. topsquark likes this.

 Tags layer, reflection, thickness

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