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Re: Projection displays

> From: Mark Spitzer <MSPITZER/>

>
> Presumably the 15 degrees is set by the angle subtended by a single pixeI,
> time the number of pixels.  I think that the telescope doesn't work
because
> it also increases the pixel (spot) size by 10x, so you end up with needing
> a yet higher FOV.

Output angle is determined by the phase delay imparted by the Bragg cell to
light crossing the acoustic axis.  The phase delay is related to product of
the optical transit time in the Bragg cell and the variation of the index of
refraction.  While you're correct in recognizing that the telescope will
increase the pixel size, you can't reasonably conclude that you need "a yet
higher FOV".  What you need is a narrower beam profile, which you can obtain
by performing spatial filtering on the input beam.

Something I forgot to mention before is that if you're using a Bragg cell,
your temporal resolution is limited by the fringe transit time across the
cell (at 617 m/s in TeO2 or 1720 m/s in water).  If you launch a chirp down
the cell, you can have a continously varying deflection angle at the cost of
increased beam width.

If instead you launch successive groups of monochromatic fringes down the
cell  the output beam will on average be narrower, but there will be periods
during which the beam is widened (i.e. mixing output angles).  You could
shut off the laser during these transitions to obtain better pixel
separation.

Finally, some groups have had success using LCDs (without polarizers) as low
efficiency phase delay elements to display CGHs.  It would be neat to see
how well you could do using one of these for beam steering.  Better yet, use
a micromirror array as a binary interferogram.

    -Rehmi

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