# How to use interferometer for surface roughness calculations?

1. Nov 18, 2012

### supernova1387

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

Last edited: Nov 18, 2012
2. Nov 19, 2012

### Andy Resnick

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. Nov 20, 2012

### supernova1387

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

Last edited: Nov 20, 2012
4. Nov 20, 2012

### Ranger Mike

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.