Michelson Interferometry: Fringe Counting and Gas Refractive Index

All flashcards

Michelson interferometer

An instrument that splits light into two paths and recombines the beams to produce interference.

Compensator plate

A plate that equalizes the glass thickness traversed by the two beams.

Michelson path difference

For mirror distances $d_1$ and $d_2$, the round-trip difference is $\Delta l=2d_1-2d_2$.

Mirror displacement from fringe count

If $m$ fringes pass, the mirror moves by $\Delta d=m\lambda_0/2$.

Gas-cell refractive index

For cell length $t$ and fringe count $m$, $n=1+m\lambda_0/(2t)$.

Quiz questions

1. What does the half-silvered mirror do when incident light reaches it in a Michelson interferometer?Answer: It reflects part of the light and transmits the rest.
2. What is the purpose of the compensator plate in a Michelson interferometer?Answer: It equalizes the glass thickness traversed by the two beams.
3. With no additional phase shift, what path difference produces a bright fringe in a Michelson interferometer?Answer: An integer multiple of the wavelength.
4. A mirror moves $210\,\text{nm}$ in an interferometer illuminated by $420\,\text{nm}$ light. How many fringes pass a fixed reference point?Answer: One fringe passes the reference point.
5. When light reflects from a medium with a greater refractive index, what phase change may occur?Answer: A phase change equivalent to half a wavelength.