Re: [tech-3d] Re: holographic screen?? (was: fresnels & episcopes)

[lunazzi <lunazzi@xxxxxxxxxxxxxx>]

webmaster@xxxxxxxxxxx wrote:
> 
> --- In tech-3d@xxxx, "sergio baldissara" <bobongo@xxxx> wrote:
> > I confess I can hardly understand what you (& other AA) mean by
> > "holographic screen"...
> 
> As i understand the screen is made using holography.
Understanding the term in a usual general sense of reproducing wavefronts,
although is not intended for reproducing wavefronts but for the hologram being a
special screen.

> In this case one
> has to use traditional holographic setups , split a laser beam into an
> object and reference beam.By using appropriate beam shaping lenses and
> mirrors one lets the beams interfere in space and records the
> interference pattern in a high resolution plate or film.This is a
> common technique used for the production of screens for pilot HUDs in
> which case the photosensitive material is dichromated gelatin.

O.K.

> By controling the two beams one can make holographic optical elements
> (HOEs) that behave as traditional lenses or systems but with the added
> advantage of less weight and better optical optimization.The best of
> all is that you can produce easily off axis systems.
> The disadvantage of HOEs is that they are pure diffraction systems so
> they dont work well with white light.

In the traditional way of using white light for imaging with refractive,
achromatic lenses.
Not if you use diffractive elements also for imaging.

. They are best suited for
> manipulation of laser light.In the case of a holographic screen one
> should be very carefull in design as to reduce image color splitting
> due to different diffraction angles at different wavelenghts.The best
> way to avoid such dispersion would be to focus at exactly the screen's
> effective focal plane and use a very well collimated reference beam
> during holography.

O.K.

Now take a look at:

http://www.geocities.com/doctorlunazzi/HORIZONTAL/HORIZONTAL.htm

Explanations, diagrams and pictures are there (in portughese)

You boys are making me work a lot, for free!  Maybe by the time you read this,
you can find the english version at:

http://www.geocities.com/doctorlunazzi/HORIZONTAL/HORIZONTAL_i.htm

Dont expect answers until next week, I must work for my classes now.

Yours,

José


 

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