How do i demonstrate thin film interference with microscope slides?

[handsomecat]

How do i demonstrate thin film interference with microscope slides?

Textbook questions all mention that you will get parallel fringes when you put a hair between two microscope slides.

However, i have tried doing so, but don't get the parallel fringes. I used a red laser pointer, and a incandescent light bulb.

Is there something that I have missed? Do i need to use polarized light?

 

[Andy Resnick]

I almost always see fringes when two slides or coverslips stick together, no special lighting needed. Try it without the hair?

 

[sophiecentaur]

You get the best results from optically flat and clean slides (dry, too). You also get them, to everyone's annoyance, when you use plane glass holders for 35mm colour slides in an old fashioned slide projector. The colour fringes are often referred to as Newton's rings but they are all sorts of shapes. The smaller the angle, the wider the fringes, of course because they recur each time the spacing increases by a half wavelength. Is your hair 'wispy' or 'coarse'?
You have to get your head in the right place to view the fringes or the direct specular reflection can mask them.

 

[handsomecat]

thanks so much. You are right that the orientation is importont. I saw the fringes!