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

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

On May 16, 2009, at 12:39 PM, Brian Whatcott wrote:

> ludwik kowalski wrote:
> > 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?

> >
> Your layout uses two half mirror traversals for leg 1 and none for  
> leg 2.
>
> It would be simpler, cheaper (and more balanced) to arrange it like  
> this
> Michelson-Morley arrangement with one half mirror and
> two front surface mirrors:
>
>
>                    screen
>                      I
>                      I
>                      I
>                      I
>      laser beam - -> \ - - - leg 1 - - |
>                      I
>                      I
>                      I
>                      I
>                      -  leg 2
>
> Seeing interference fringes requires no great effort.

Thanks Brian,

1) Michelson-Morly interferomentrs are standard equipment in many  
schools. No optical table is needed. It is simply matter of removing  
the sodium lamp and sending a sufficiently wide laser beam into the  
beam splitter.

2) Perhaps someone will be able to do this, and share the results with  
us. I was not thinking about "interference fringes;" I expect the  
glass area covered by a thin foil to be either much darker or much  
brighter that the area that is not covered. The contrast will depend  
on the film thickness. That would be an excellent demo for students.

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