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

[ludwik kowalski <kowalskil@mail.montclair.edu>]

On May 16, 2009, at 1:52 AM, Bernard Cleyet wrote:

> That's fixed by using very "good" lenses and adding a pinhole
> (spacial filter).
>
> bc
>
> p.s. pinhole mitigates many evils at the expense of intensity loss.
> The better the source, etc. the less loss.
>
> On 2009, May 15, , at 11:18, ludwik kowalski wrote:
>
> > 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.

Thanks for the comment, Bernard.

If I had access to an optical table then I would make an attempt to  
verify my dreamed idea, unless persuaded that it is also silly.  
Placing my laser 15 meters away from the setup would produce a wide- 
enough beam, without a pinhole.

                                                                                                                       I
wide laser beam - -> \ - - - leg 1 - - > / - - - > I
                     I                   ^         I
                     I                   I     screen
                     I                   I
                     I                   I
                     \ - - - leg 2 - - > /


Upper slashed lines (in leg 1) represent semitransparent mirrors,  
lower slashed lines represent ordinary mirrors. Suppose a microscopic  
slide, partially covered with a transparent thin film, is introduced  
into leg 1.  My expectation is that interference of two beams  
(observed on the screen), traversing the slide and not traversing the  
slide, will result in phase contrast. That demonstration (turning an  
invisible  "phase image" into a visible "amplitude image," would be  
easier to understand than what happens in a phase microscope. Is there  
anything thing wrong with this idea?

- - - - - - - - - - - - - -
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