# Insights Fabry-Perot and Michelson Interferometry: A Fundamental Approach - Comments

Tags:
1. Jan 2, 2017

2. Jan 2, 2017

### houlahound

Only skimmed ATM, looks like another great insight.

Thanks.

3. Jan 3, 2017

### Staff: Admin

Great first Insight Charles!

4. Jan 3, 2017

### Charles Link

Perhaps one thing worth mentioning in more detail that I only included in one sentence in the article is that it can also be applied to sinusoidal r-f voltage signals traveling on a transmission line and incident on an interface where the characteristic impedance changes. The same reflection and transmission coefficients apply with $n_1$ replaced by $\frac{1}{Z_1}$, and $n_2$ replaced by $\frac{1}{Z_2}$, and the electric field $E$ replaced by voltages. (In the r-f case I don't think they call them "Fresnel" coefficients, but the equations are the same with the replacement just mentioned. And of course the energy/power goes as $V^2/Z$ ) .It will even work for two voltage pulses traveling on a transmission line. Instead of having the signals $\pi$ out of phase, one of them can be a pulse with a negative voltage. @Dale I think you are an electrical engineer=perhaps you would find the r-f case of interest.

5. Jan 3, 2017

### houlahound

That would be good to edit into the original article, not everyone will see your last post.

6. Jan 3, 2017

### Charles Link

Thank you @houlahound I took your suggestion and added a paragraph at the bottom. :)

7. Jan 3, 2017

### Charles Link

Just one additional comment that doesn't need to be part of the article: I believe the radar that the police use is essentially a Michelson type configuration, possibly with microwaves, where the vehicle being measured for its speed is basically one of the Michelson mirrors. The returning Doppler shifted sinusoidal signal is heterodyned with the internal reference signal (the two signals are combined and the beat frequency observed). For microwaves, an optical type beamsplitter would not be necessary, but otherwise, the principles are similar.

Last edited: Jan 3, 2017
8. Jan 3, 2017

### houlahound

I think microwave speed detectors for police use are obsolete. They have laser systems now. From what I can tell.

What you said prolly still holds tho.

9. Jan 3, 2017

### Charles Link

I should point out that for the case of the moving Michelson mirror, there are two ways of analyzing the system that yield identical results: 1) As the interference of the two signals that causes constructive or destructive interference with the result changing with time because of the changing relative phase of the two signals due to the changing path distance as a function of time 2) As a frequency shift (Doppler shift) of the returning signal from one of the mirrors.

10. Jan 12, 2017

### vanhees71

That's a very nice Insights article!

11. Jan 12, 2017

### Charles Link

Thank you @vanhees71

12. Jan 16, 2017

### Staff: Admin

Last edited: Jan 16, 2017
13. Jan 2, 2018

### Charles Link

A student just posted a homework question involving the Michelson interferometer in the form where the source is a diffuse source rather than a plane wave. The concepts presented in this Insight article are still relevant, and anyone with an interest in interferometry may find this homework question of interest: https://www.physicsforums.com/threa...michelson-interferometer.933638/#post-5902650 $\\$ This experiment of the interference fringes of the sodium doublet using a Michelson interferometer is performed on occasion in an Optics class that includes laboratory experiments. My classmates and I performed such an experiment in the upper level undergraduate Optics course at the University of Illinois at Urbana in 1976. We did successfully show that the lines of the doublet are separated by $\Delta \lambda \approx 6.0$ Angstroms.

Last edited: Jan 3, 2018
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted