How to use interferometer for surface roughness calculations?

In summary, an interferometer can help measure surface roughness but it is difficult to convert fringe distances to meaningful data.
  • #1
supernova1387
31
0
Dear all

I am working on a project and I need to measure the surface roughness of a specific type of wood. I don't want to make things complicated because I have to make the instrument myself. I think an interferometer can help me to measure surface roughness but I really don't know how to convert the fringe distances etc to any meaningful data for surface roughness. If anyone has done any similar thing or has any knowledge on measuring surface roughness please let me know

Regards
 
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  • #2
Shearing interferometry is a standard method for surface profilometry:

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-8-11-2173
http://www.aspe.net/publications/Annual_2001/pdf/posters/metro/surf/1128.pdf
http://www.scientific.net/KEM.321-323.99

But I don't know if you can apply the technique to wood- wood is not reflective, but scatters diffusely; also, the surface features of machined wood are quite different from machined metal.

I did find this, tho:

http://www.jpier.org/PIER/pier80/15.07112706.pdf
 
  • #3
Thank you for your reply but don't have access to the first and 3rd papers.

You are right, but what if we use a reflective surface? I found these papers too but I don't know how to put them into practice. If you or anyone else wants to share knowledge you are most welcome. Unfortunately, many papers omit the construction details and just focus on the equations and theory which makes it difficult for an amateur like me. I had come across surface roughness problems in the past, so I really want to be able to measure surface roughness by making an instrument myself :). The surface itself is not an issue yet as long as I can make an instrument myself. I mean I can use steel instead of wood or another reflective material.

http://www.eng.auburn.edu/users/htippur/papers/sinha-tippur-oe.pdf

http://fp.optics.arizona.edu/jcwyan...ptical_Testing/10.6 Micron Interferometry.pdf
 
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  • #4
Having been Product Manager for the company that invented the Profilometer in 1938, I feel qualified to discuss this. The ANSI B46 standard on Surface Texture details the parameters for Surface Roughness assessment. In the practical world I have sold industrial lasers over the years for various measurement of machine geometry or dimensional measurement. Lasers have problems with highly reflective surfaces. Addionally the peak to valley excursions that must be measured by the instrument must be within the instruments range and laser system detectors do not readily lend them selves to this micro measurement. Over the years there was a trend to use capacitance measurement to qualify a steel surfaces properties and this too had a limited range. Dr. Ken Ludema did some work on Laser elisometry trying to qualify surface parameter though I think a product was never marketed. It seems that the skid mount refrenced tactile method of a diamond stylus and motorized pilotor is still cheapest and best.
 
  • #5
,

I can provide some guidance on how to use an interferometer for surface roughness calculations. An interferometer is an optical instrument that measures the variation in the shape of a surface by analyzing the interference pattern of reflected light. In order to use an interferometer for surface roughness measurements, you will need to follow these steps:

1. Set up the interferometer: The first step is to set up the interferometer properly. This involves aligning the light source, the mirrors, and the detector to ensure that the reflected light creates an interference pattern.

2. Prepare the sample: The sample surface needs to be clean and free of any dust or debris. The surface should also be flat and parallel to the interferometer's reference surface.

3. Take measurements: Once the interferometer is set up and the sample is prepared, you can start taking measurements. The interferometer will produce an interference pattern that consists of bright and dark fringes. The spacing between these fringes is directly related to the surface roughness of the sample.

4. Convert fringe distances to surface roughness: To convert the fringe distances to surface roughness values, you will need to use a mathematical formula. This formula takes into account the wavelength of the light used, the angle of incidence, and the spacing between the fringes. You can find this formula in most interferometer manuals or online resources.

5. Repeat measurements: It is important to take multiple measurements at different locations on the sample surface to ensure accuracy. You can then calculate the average surface roughness value for your sample.

In conclusion, an interferometer can be a useful tool for measuring surface roughness. However, it is important to set it up correctly, take multiple measurements, and use the appropriate formula to convert fringe distances to surface roughness values. I hope this helps and best of luck with your project.
 

1. What is an interferometer?

An interferometer is a scientific instrument used to measure the interference patterns of light waves, allowing for precise measurements of small changes in distance or surface roughness.

2. How does an interferometer work?

An interferometer uses a beam splitter to split a single light beam into two beams, which are then recombined at a detector. The resulting interference pattern is measured and analyzed to determine changes in the distance or surface roughness of the object being measured.

3. What are the advantages of using an interferometer for surface roughness calculations?

Interferometers offer high precision and accuracy in surface roughness measurements, as they can detect changes on a nanometer scale. They are also non-contact, making them ideal for delicate or sensitive surfaces.

4. What factors can affect the accuracy of interferometer measurements?

The accuracy of interferometer measurements can be affected by environmental factors such as vibrations, temperature changes, and air currents. The quality and alignment of the optical components can also impact the accuracy of the measurements.

5. Are there different types of interferometers for surface roughness calculations?

Yes, there are several types of interferometers used for surface roughness calculations, including white light interferometers, laser interferometers, and scanning probe microscopes. Each type has its own advantages and limitations, and the choice of which to use may depend on the specific application and surface being measured.

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