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Re: [Phys-l] A demo for biologists?



P.P.S.
The process of expanding the beam with two lenses will probably destroy spacial coherence (because different "bundles of rays" travel through different thicknesses of glass in lenses). Placing the laser far away from the slide should produce a large enough (but still specially coherent) beam for the suggested below demonstration.

On May 15, 2009, at 11:19 AM, ludwik kowalski wrote:

P.S.
A single expended beam seems to be a better, and simpler to implement,
approach.

Ludwik

On May 15, 2009, at 11:00 AM, ludwik kowalski wrote:


One thing that biology students would probably appreciate is a good
demo of "phase imaging." Here is an idea that I have never tried.

Suppose a laser beam is expended (with two lenses) to a diameter of
about 1 cm^2. Then it is split into two beams, like in an
interferometer, and recombined into one beam projected into a screen.
Suppose a small piece of glass (a microscopic slide) or plastic is
partially covered with a transparent foil of thin plastic (mylar).
Placing this transparent object into one of the beams would probably
create a contrast (for example, mylar-coated area being darker or
brighter that the other area. Stretching the film (reduction of
thickness) would probably change the contrast.

Have someone tried such demonstration? Biologists often use phase
microscopy without understanding it. Such demo, if it works, would
probably by appreciated by many. This idea, by the way, came to me in
a dream, last night.



- - - - - - - - - - - - - -
Ludwik Kowalski, a retired physics teacher and an amateur journalist. Updated links to publications and reviews are at:

http://csam.montclair.edu/~kowalski/cf/ http://csam.montclair.edu/~kowalski/my_opeds.html http://csam.montclair.edu/~kowalski/revcom.html

Also an ESSAY ON ECONOMICS at: http://csam.montclair.edu/~kowalski/economy/essay9.html