On 23/12/2013 02:37 PM, scott wrote:
>> I also found a website with software for computing interference
>> patterns. They claim that if you take something like a 600 DPI laser
>> printer and print the pattern onto a transparency, you can shine a laser
>> pointer through it and get a very fuzzy, very grainy hologram.
>
> Oooh that sounds interesting, might have to give that a go. I got one of
> those cheap $20 green laser pointers, if you focus it it's enough to
> light a match or melt your name into anything plastic :-)

Knock yourself out:

http://corticalcafe.com/software_onlineCGHinstructions.htm

They demo it with a red laser; I don't know if that's crucial. (The 
laser wavelength is probably adjustable in the program...)

>> CD? Perhaps not; CDs don't use visible light, they use infra-red, so the
>> dot pitch might not be small enough.
>
> Well if a 600dpi print just about works, then by my rough estimations a
> CD should be about 20000 dpi. Maybe not perfect, but it works.

Yeah, I've been sat here trying to figure out what the actual DPI of one 
of these disks is. I guess it requires knowing how many inches per meter 
there are. :-P

>> A DVD, on the other hand, uses a
>> red laser, so it certainly ought to be able to do a red-light hologram
>> without difficulty. (Provided you can convince the drive to put the dots
>> where you want them!)
>
> You can't without modifying the drive. IIRC they had to bypass pretty
> much the whole signal path and just drive the laser directly (well not
> quite, but you get the idea).

Doesn't LightScribe help here? Or does that only allow you to specify a 
grey level, which the device itself then dithers?

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