LASERS! && Freemont Street LED array (was Re: Cray J932SE (was Re: Straight 8 up on Ebay just now))

[ethan at 757.org]

> Yeah, me too, but my impression is that they're only for pre-prepared
> displays, and only some displays (notably those that don't involve the
> beam turning any sharp corners, such as Lissajous figures).
> My impression may, of course, have been - be - incorrect, which is what
> I'm asking for; if you've seen such displays involving sharp-corner
> turns of the beam and run-time chosen displays, then obviously my
> impression is incorrect and the technology exists.

The devices are called Galvometers and they work like audio meters. There 
is in deed a mirror, and they are used in an XY pair. Old gas lasers used 
a RF driven crystal to select a specific wavelength of light (and deflect 
all other wavelengths.) Those crystal setups are known as Poly-chromatic 
acouso-optic modulation or PCAOM for short.

The current fastest scanners that I know of on the market for laser show 
display would be the Pangolin Saturns. Next up would be something in the 
6800 series from Cambridge Technology.

The galvos can do sharp turns, text, and graphics. There is software for 
Linux that can do edge tracing and send it out of a modified sound card 
DAC (has to pass DC voltage?) to the X/Y scanner drivers. Most galvos have 
a feedback loop for inertial correction.

The laser display world uses a test frame known as the ILDA (International 
Laser Display Association) and there is a performance benchmark in points 
per second, so 12,000 points per second is old spec, 30,000 points per 
second is a newer spec. Now people are claiming 60 and 90K on the modern, 
expensive, quality scanners. The Chinese stuff is mostly 30K and 40K. The 
old days 8 degrees was the scan width but now people push it way further.

Old technology stored the laser show information on various formats for 
shows ... like 8 track multitrack reel to reel, and then the Alesis SVHS 
based ADAT machines were popular for a while. Now everything is directly 
driven from computer.

Some of the old systems are being recovered here and there, and similar to 
vintage computers people pet them and clean them and take care of them. 
I'm pretty certain some old school stuff existed in the S100 world, but 
none of that has surfaced. There is also analog consoles and the like.

As far as sending video from a computer frame buffer, I think it might be 
way too fast. Also, the more you scan and the faster you scan the laser 
power has to be higher. And there can also be issues with modulating the 
actual laser diodes. Direct solid state run at one rate and diode pumped 
solid state run at another rate.

This is a random picking of a laser graphics show, projected on a scrim. 
It's from LD-2000 which would of been Windows 2000 to XP era software, but 
the show is pushed into a card that is a Motorola 68040 on a board with 
RAM where the card just runs the show once it's loaded. Pangolin's roots 
are on the Amiga so I've always grinned thinking they just put an Amiga on 
a board:

https://www.youtube.com/watch?v=khVGAOLTaTA

There are a few ports of MAME for running vector arcade games into laser 
projectors, the older hardware had quite a bit of flicker.

There is also someone who has rebuilt, from scratch, several older analog 
consoles that had some fame.

China really opened the floodgates with the availability of parts, and 
lots of projectors and low cost galvos. Before China a set of galvos could 
run a thousand or more dollars with the amps. And the PCAOM hardware would 
costs thousands. When I had the argon system I had picked it up from a 
NASA auction while hunting lasers, SGIs, and Suns.

Everyone will probably cry when I say that one of the first NASA auctions 
I went to there was a Convex system there.