# 180 degree phase shift of reflected light

• ramsd
In summary, when light reflects off a surface of higher refractive index from a medium of lower refractive index, the phase shift is 180 degrees due to Stokes relations showing equal but opposite reflection coefficients. The magnetic component of the incident ray induces a perpendicular current in the mirror, generating a perpendicular magnetic field that cancels the incident ray. This energy is then reflected due to the current flowing on the mirror surface. The explanation for the 180 degree phase shift is due to the reflection of the incident ray and the cancellation of the perpendicular magnetic field. Thanks to Baluncore for providing this clarification.
ramsd
When light originating from a medium of lower refractive index reflects off a surface of higher refractive index, why does the phase shift by 180 degrees? Stokes relations show that reflection coefficients at the surface are equal but of opposite signs depending on direction of light (i.e. from lower to higher refractive index versus higher to lower); but Stokes relation does not tell me explicitly which one is shifted by 180 degrees. Can someone please provide an explanation for this. I have researched the internet with no success. Thank you in advance.

The magnetic component of the incident ray induces a perpendicular current in the mirror. That current generates a perpendicular magnetic field, that cancels the incident ray into the mirror.
The energy that is reflected is due to the current flowing on the mirror surface.

i·i = i² = -1.
Rotating 90° twice makes 180°.

Baluncore said:
The magnetic component of the incident ray induces a perpendicular current in the mirror. That current generates a perpendicular magnetic field, that cancels the incident ray into the mirror.
The energy that is reflected is due to the current flowing on the mirror surface.

i·i = i² = -1.
Rotating 90° twice makes 180°.
Thanks Baluncore, that clears it up.

## 1. What is a 180 degree phase shift of reflected light?

A 180 degree phase shift of reflected light refers to the phenomenon where light waves are reflected off a surface and the phase of the reflected wave is inverted by 180 degrees compared to the incident wave. This means that the peaks of the incident wave become the troughs of the reflected wave, and vice versa.

## 2. What causes a 180 degree phase shift of reflected light?

A 180 degree phase shift of reflected light is caused by the interaction between the incident light wave and the surface it is reflected off of. The surface may have different properties, such as a different refractive index, which can cause the phase shift to occur.

## 3. How is a 180 degree phase shift of reflected light measured?

A 180 degree phase shift of reflected light can be measured using various techniques, such as interferometry or polarimetry. These methods involve analyzing the interference patterns or polarization changes of the reflected light to determine the phase shift.

## 4. What are the applications of a 180 degree phase shift of reflected light?

A 180 degree phase shift of reflected light has various applications in optics and photonics. It is used in devices such as interferometers, polarizers, and optical switches. It is also important in optical communication systems and in measuring the thickness of thin films.

## 5. Can a 180 degree phase shift of reflected light be controlled?

Yes, a 180 degree phase shift of reflected light can be controlled by adjusting the properties of the surface it is reflected off of. For example, changing the refractive index or the angle of incidence can alter the amount of phase shift that occurs. This control is essential in many optical devices and systems.

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