ATM Fringes again: another light source

[Scott Rychnovsky <srychnov@chem.ps.uci.edu>]

I was trying to see fringes to inspect a convex secondary.  I used 
one of the low-wattage "energy conservation" fluorescent lights made 
to screw into a standard light bulb socket.  It worked OK, but it 
gave a rainbow of fringes which is distracting when you only have a 
few fringes showing.

I found a much better light source yesterday. I took my cheap, hand 
held laser pointer and used some putty to stick a 1 cm lens on the 
front.  This spread out the beam, but didn't give clear fringes. 
Over this lens I attached some tissue paper (lens paper?  very thin) 
with a bit more putty.  Now the laser beam is dispersed and perhaps 
scattered a bit.  This light source worked and gave very nice, clean 
fringes!  The fringes are much cleaner than with the fluorescent 
bulb.  The red lasers are all reasonably monochromatic with a 650 nm 
beam.

Most of us have a laser pointer around.  I would recommend this light 
source as a quick solution to seeing fringes.  You need a dispersing 
lens, but I don't think the type of lens is really important--just 
something to spread out the beam.  The tissue paper could be replaced 
by frosted glass or something else to scatter the beam.  There may be 
better light sources for observing fringes, such as filtered Mercury 
lights, but this one is cheap and easy.

Scott
--
Scott Rychnovsky
srychnov@chem.ps.uci.edu