optical flat

Hi, Optical flats are viewed through a polarized lens. The closer the lines in a given area, the less flat you are. What you are viewing is the nodes and anti-nodes of the wave of the light. In other words, the dark areas, are the anti nodes. The light has destroyed it self. Simple wave theory. The further your bands are apart the more flat you are. The interference (dark lines), I think you are calling fringes, are part of it. They are the half wave lengths of the light. Count two dark, or two lighter areas and that gives you the a single wave length. The normal optical flat should be restricted to 3 wave lengths, a cross the total surface. So six lines, light, dark, gives the proper flatness. The less lines the better. Physics 101 books have simple wave theory look towards the back. Short chapter.

Hope this helps

Shape of pattern as well as number of lines indicates surface condition.

If you could send me your email I could send you a .pdf that will explain. I have been unable to attache .pdf's to my correspondence on CR4.

milo

Ya sure its rwplews@yahoo.com. I don't know if I'll be able to help,but I know lots of folks that can.

Hi,

any these fringes can be thought as height differences between the two plates.

(This is equivalent to height lines on maps.)

Vertical distance between any two dark lines is near 0.3µm if red Laser is used as a light source.

If you draw a straight line tangentially to one of your dark lines and then count how many other dark lines are crossed by this straight line this multiplied by 0.3µm you will get the height difference along this straight line.

There exist automatic computerised frame grabber and calculating programs that calculate fringe to color coded height maps.

Have a look into the books on interferometry from SPIE.org or from Malacara.

RHABE

This description will give you the basics, the subject was also covered fairly comprehensively in a previous CR4 thread here.