8 Mar
2007
8 Mar
'07
6:23 p.m.
Hi,
High BW laser deflection is often done with "Bragg cells". They are
acousto-optic.
You input signals at NN Mc. and the cell essentially changes its
refractive index. As beam shines through, it is deflected.
Not inexpensive. When you design a display for human use, psychopyhsics
very important.
You need to think about energy/unit time, deflection, persistence,
retinal sensitivity, etc.
Many clever people spent their lives working on phosphors.
Sooner or later you get back to Farnsworth and Logie-Baird equivalents.
Back when much of the stuff on this list was new, there was a project
involving 30 Mc. BW laser deflection for writing directly on wafer.
Not sure of current speeds, BW, but bound to be faster.
BR,
Steve
ionder Mouse wrote:
Somehow I got
subscribed to an optics catalog. This got me to
thinking. How hard would it be to cause a laser beam to sweep with
the speed and accuracy to be a substitute for a CRT?
Quite easy. Barcode scanners do it regularly in one dimension; you
just need to add another, much slower, scan in the other dimension....
How hard would it be to do it affordably, safely, etc? That's another
question. Note that horizontal scan frequences in the high tens of KHz
are common; you'll have to be scanning something like that fast on the
"fast" axis. Given (say) a 20-faced mirror spinner (which might be
good enough, though it might prove not linear enough), a scan rate of
80KHz (what the display I'm using right now is doing) means this
thing's RPM would be 80,000 (scans/sec) * 60 (sec/min) / 20 (scans/rev)
= 240,000. 240K RPM is pretty bleedin' fast! Perhaps you can find a
video card that can do something like 1024x768 at 20? Most video cards
are concerned with achieving high, not low, refresh rates....
Does anyone know of any electrically controlled optical deflection
technology that has sub-microsecond reaction times? I seem to recall
seeing that some crystals change their refractive index with applied
voltage; if I'm not misremembering, and if they change fast enough,
that might do.
I'd actually prefer to use such a thing not as a raster display, but as
a vector display - hence the interest in electrically deflecting the
beam. I'd like to play vector videogames on a big white wall - either
classic games under something like MAME, or my own....
The upshot? Take an old terminal with nasty
screen burn. Cut off
the gun end of the bottle, clean off the old phosphor. Apply new
phosphor of some kind, then mount the laser rasteriser where the old
gun was.
Neat idea.
Projecting raster images on the side of a building
would be fun too.
But you'd need to crank the laser intensity way up. Even then it might
not be usable except at night. :)
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