# 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

### Greg Bernhardt

Great first Insight Charles!

4. Jan 3, 2017

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

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

7. Jan 3, 2017

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

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

Thank you @vanhees71

12. Jan 16, 2017