Reflection and Refraction Ranking by Phase Shifts

[bokonon]

1. A ray of light is incident onto the interface between material 1 and material 2. There is a figure, which is a standard figure of a ray in medium of n1 striking an interface where medium2 (with n2) meets medium1. As is typical, some of the light is reflected and some is refracted.

The question asks: Given the indices of refraction n1 and n2 of material 1 and material 2, respectively, rank these scenarios on the basis of the phase shift in the refracted ray. And then goes on to list different scenarios (e.g n1=1.33, n2=1.46 vs n1=1.33 n2=1.0).

The second part is the same, but asks to rank based on the phase shift in the REFLECTED ray.

2. This question is a lot different from standard ray optics questions, and I wonder why there is any phase shift at all, unless the refracted ray meets another interface where it can reflect/refract and thenTHAT reflected ray would have a phase shift from the first refracted ray, because it has traveled a different distance through medium 2. But how can you compare the phase shifts of two different refracted rays? I feel like I am missing something. Any suggestions? Thanks.

 

[Chi Meson]

There is no phase shift as a ray is transmitted into a new medium. There is a phase shift when the ray is reflected in certain conditions. Do you know what those conditions are?

 

[bokonon]

So you're saying that the answer to the first part of the question is that all of the different conditions for the indices of refraction make no difference, as no refracted rays experience a phase shift?

I'm thinking for the reflected rays there is a phase shift when n2>n1, intuitively I'd guess that the bigger the difference the greater the phase shift, but I can't picture how this works at all. If the rays are all just bouncing off the interface, then why would there phases change?

 

[Chi Meson]

The phase shift is either 180˚ (1/2 wavelength) or none at all. It is determined by the interface being fast to slow, or slow to fast mediums.

 

[bokonon]

"The phase shift is either 180˚ (1/2 wavelength) or none at all. It is determined by the interface being fast to slow, or slow to fast mediums."

You're speaking strictly about reflected rays, right? I'm still confused about why there are any phase shifts at all.

Thanks

 

[Chi Meson]

You're speaking strictly about reflected rays, right? I'm still confused about why there are any phase shifts at all.

Thanks

So are we all. The mechanical wave (wave on a string) has a simple explanation
http://www.kettering.edu/~drussell/Demos/reflect/reflect.html

the reason why light also does the same, even one photon at a time, requires knowledge of quantum electrodynamics (QED). Just let it go for now ;-)

 

[Physics Mom]

A good investigation into phase shift, will show that for the REFRACTION (that is, the transmitted ray), the phase shift should depend on (n2-n1), so any variety of interfaces can easily be ranked. Of course, the distance/time in the medium and the wavelength of the light.

Here is one set of lecture notes which goes further into this topic http://www.physics.pdx.edu/~larosaa/Ph-223/larosa_lecture10_ph_223.pdf