Fizeau Interferometry

[pluto]

Hello,

I'm trying to get an idea of how big of an issue vibration will be. I often hear about people using Michelson interferometers for this.

I don't have a beam splitter cube or a half silvered mirror yet, so I was wondering if anybody has used Fizeau interferometry to gauge the amount of vibration.

I set up a Fizeau interferometer and did observe fringes with high contrast, but I became suspicious when walking around the setup did not affect the fringes. I have to tap very near to the setup to get fringe movement.

I set up my interferometer by shining the laser beam through a beam expander and reflecting it off a tilted piece of glass almost directly behind the laser head.

I'm not completely sure how it should be setup. Would the distance between laser head, beam expander and projection surface affect the sensitivity or "resolution" of the fringes?

Thanks!

[Ed Wesly]

A picture of your set up would be helpful!

[holomaker]

A Fizeau interferometer is for watching for stability of the laser only, you can make a Michelson interferometer , just use a piece of plate glass as you're beam splitter you may only get 10% and 90% but it's better than not having anything

[pluto]

So could this type of interferometer be used to detect mode hopping?

I think I'll give the Michelson a go, but I need to think of a better way to mount and position mirrors, it can be quite a pain...

[holomaker]

Below is a picture of what you should see as u are bouncing the expanded beam off the glass slide and directed
back towards the laser's origin

image.jpeg (726.67 KiB) Viewed 3340 times

I think I'll give the Michelson a go, but I need to think of a better way to mount and position mirrors, it can be quite a pain...

I suggest you referred to the holo wiki section on homemade components ,we've all been there and done that it will be something that you necessarily need in the future as much of a pain in the ass that it is .....

Yes in the Fizeau interferometer will show you if there is any mode hopping aka(stability) of the laser. Also when tuning your lasers out put this will insure you are tuned to a "sweet spot"....

[holomaker]

Simple components can be made by a block of metal with plasticine stuck to it , and that's not difficult at all

[lobaz]

If you can, use a really thick piece of glass as a beamsplitter. It helps to block unwanted ray reflections from the back surface to the glass plate. Thicker = better, see the picture.

Alignment procedure:

1. Switch on the laser. Set up mirror 1. Do not align it precisely - it is not wise to bounce the ray back to the laser cavity.
2. Insert the glass plate, try to achieve 45 degrees. Put a sheet of paper somewhere where the mirror 2 is supposed to be, and cover the beamsplitter so that the backreflected (magenta) ray is blocked.
3. Insert the mirror 2. Adjust it so that the beams overlap on the screen. Be careful - you don't want to reflect the the beam back to the laser.
4. Insert the lens. You should see many fringes now.
5. Slightly tap the setup. Some of the fringes should disappear. Those are the fringes you should watch.
6. Enjoy vibrations.

michelson.png (16.84 KiB) Viewed 3326 times