Do I understand the Fizeau interferometer? How to read interferogram?

In summary, the Fizeau interferometer works by shining light through a collimating lens and then through a partially-reflective reference flat. The light that goes through the reference continues on and then bounces off of the test surface. As this light passes upward through the reference flat, it interferes with the light that is initially reflected off of the reference flat. This creates the interference waves. This is then reflected off of the beamsplitter and then passes through another lens. Finally you can analyze the interferogram.
  • #1
adamjts
24
0
Hi,

I'm just wondering if someone could help me better understand how the Fizeau interferometer works...http://upload.wikimedia.org/wikipedia/commons/2/2f/Fizeau_interferometer_testing_optical_flat.svg

From my understanding, the source shines light through a collimating lens and the light goes through the beam splitter. After the light goes through the beam splitter, in goes through a partially-reflective reference flat. The light that goes through the reference continues on and then bounces off of the test surface. As this light passes upward through the reference flat, it interferes with the light that is initially reflected off of the reference flat. This creates the interference waves. This is then reflected off of the beamsplitter and then passes through another lens. Finally you can analyze the interferogram. Is this understanding correct? I'm mainly confused about where the light waves really interfere. Does it interfere as the light passes through the reference or does it interfere where the two lines in the above diagram are merged? Or both?

Also, What would the interferogram look like if I had a perfectly horizontal reference, and a slightly incline test flat? Could you tell what the angle of the test flat is based on this interferogram?
 
Engineering news on Phys.org
  • #2
I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?
 
  • #3
I am far from an expert on interferometry and I wasn't going to post on this question for that reason. But you haven't had much response so I can reply from a user's point of view.

I don't know if your interferometer will work, but it looks feasible enough that I would probably build it and see.

The light source should produce coherent light and it is typically a helium/neon (he/ne) or diode laser with a wavelength around 650 nm.

I expect you already know that it will work by producing images of interference of light waves. This interference is (in turn) additive and destructive at the wavelength of the light coming from the source.

So if your optical system is perfect and your plate perfectly flat and perpendicular to the beam you wouldn't see any interference and your image would have even illumination.

If your plate was tilted you would see interference relative to the amount of tilt. The interference pattern produces "fringes". You can count these and multiply by the wavelength to get a measurement of the tilt.

If you know the beam diameter you could convert the measurement to an angle.

Have a look at the tutorials on the following site for more information.
http://www.grahamoptical.com/phase.html
Figure 2 on this page shows tilt being removed. Notice how the amount of fringes decreases towards zero.

As above, if it was me and I had the resources I would learn by building it.
 
Last edited:
  • Like
Likes 1 person
  • #4
This is perfect! Thanks so much. very helpful
 
  • #5


Hi there,

Your understanding of the Fizeau interferometer is mostly correct. The key principle behind the Fizeau interferometer is the interference of light waves. In this setup, the light waves from the source are divided into two beams by the beam splitter - one that travels towards the reference flat and one that travels towards the test surface. The light waves that are reflected back from both surfaces then interfere with each other, resulting in the interference pattern that can be seen in the interferogram.

The interference occurs at both the reference flat and the test surface. The light waves that pass through the reference flat interfere with the light waves that are initially reflected off of it. Similarly, the light waves that pass through the test surface interfere with the light waves that are initially reflected off of it. This creates the interference pattern that is observed in the interferogram.

To answer your second question, the interferogram would show a series of concentric rings, with the center representing the point where the two surfaces are in contact. The angle of the test flat can be determined by analyzing the shape and spacing of these rings. A perfectly horizontal reference and a slightly inclined test flat would result in a distorted pattern with the rings appearing elliptical instead of circular. The angle of the test flat can be calculated by measuring the ellipticity of the rings.

I hope this helps clarify your understanding of the Fizeau interferometer. Let me know if you have any further questions.
 

1. What is a Fizeau interferometer?

A Fizeau interferometer is an instrument used to measure the flatness and parallelism of surfaces. It works by splitting a beam of light into two paths, reflecting one off a reference surface and the other off the surface being tested, and then recombining them to create an interference pattern. This pattern can be analyzed to determine the flatness and parallelism of the surface being tested.

2. How does a Fizeau interferometer work?

A Fizeau interferometer works by using a beam splitter to divide a beam of light into two paths. One path reflects off a reference surface and the other reflects off the surface being tested. The two paths are then recombined and the resulting interference pattern is analyzed to determine the flatness and parallelism of the surface being tested.

3. What is an interferogram and how is it read?

An interferogram is the interference pattern created by a Fizeau interferometer. It consists of bright and dark fringes that correspond to variations in the surface being tested. To read an interferogram, the fringes are counted and their spacing is measured. This information is then used to calculate the flatness and parallelism of the surface being tested.

4. What factors can affect the accuracy of a Fizeau interferometer?

The accuracy of a Fizeau interferometer can be affected by various factors, such as the quality of the optics, the stability of the light source, and the alignment of the instrument. Environmental conditions, such as temperature and vibration, can also impact the accuracy of the measurements.

5. How can I improve my understanding of the Fizeau interferometer and reading interferograms?

To improve your understanding of the Fizeau interferometer and reading interferograms, you can refer to technical manuals and textbooks, attend training courses or workshops, and practice with different samples. It can also be helpful to consult with experienced colleagues or seek guidance from experts in the field.

Similar threads

Replies
7
Views
2K
  • Quantum Physics
Replies
13
Views
468
Replies
14
Views
1K
  • Advanced Physics Homework Help
Replies
1
Views
2K
  • Special and General Relativity
Replies
16
Views
2K
  • Introductory Physics Homework Help
Replies
1
Views
1K
Replies
3
Views
649
Replies
1
Views
1K
  • Quantum Physics
Replies
15
Views
3K
  • Special and General Relativity
Replies
6
Views
1K
Back
Top