Modulating a Laser Beam

Why not an LCD screen you can blink it on and off.

Hmm- I think I might have seen something like that- a clock or something

Thanks! I'll try googling "LCD screen" The only problem might be heat dissipation in the screen. Interesting though. I'll see what I can find. Do you have a link?

How about the micro-mirror chips they use for digital projection TV? You could attenuate the average power by pulse width modulating the beam.

Cool! Thanks! I'll try try to find some info---

I think TI makes them.

TI DMD 1100 chipset for projection TV: $6000 usd

<sigh> oh well..

http://www.tyrexsales.com/integrated-services/dmd-discovery/1100-controller-board/

try www.dlp.com. $6K is more than these TVs cost.

Well that's what I thought!

I searched, but I don't think that the .98 DLP chip is available to the public yet.

You cannot use AOM, can you use EOM?

You say other than mechanical, is it because of speed?

If you go piezo, you could either make a shutter or beam steering mechanism/trap that can go that fast. This could be not too costly or complicated.

For a more esoteric solution, there are electro-absorption modulators, but not much info on products is available but I believe your laser would need to be in a waveguide/fiber.

Quote>"You cannot use AOM, can you use EOM?"

Expense is mainly the reason. This is a personal project; non-funded.

Yes indeed there are several methods.

The simplest and least expensive is to start with a Laser Diode. A Laser Diode is a low voltage device and its light output can be varied from on to off and any thing in between. Do NOT drive it with a voltage source. A variable current source is the proper method. Laser diodes come in a wide range of wave lenghts (colors) and output powers. CAUTION You can damage you eyes. Please be careful. If you want a visable light choose a wave length 635 - 650 nanometers. These are available in a wide variety of wave length and power and are not very expensive. Laser diodes are very sensitive to static electricity, so use care when handling. Green are also available but more expensive. Jameco is one of many sources. Google will also help you find lots of info on both Lasers and the drivers. Many of the IC manufacturers make the drivers. There are also simple circuits that you can build using basic electronic components.

LCDs and Pockel cells used in conjunction with polarizers is an other way to modulate light but this is much more expensive.

Look around a bit and / or post quiry if you need more info.

This is typically done with a polarized beam and a kerr or pockels cell.

http://en.wikipedia.org/wiki/Pockels_effect

http://en.wikipedia.org/wiki/Kerr_effect

A revolving faceted mirror may be the answer for you as a quick and simple method. Only allowing the laser light thru a single small hole after reflecting off each facet.

Early laser printers "scanned" the semiconductor drum with such a device years ago (20?) to form the characters to be printed. So you may get the mirror and the motor from an old type Laser printer that is being junked. Checkout laser printers from StorageTek (Siemens Built), Siemens and IBM - to name but a few....

Even building one yourself should not be too difficult......

Two similar technologies exist which allow for externally modulating a CW laser beam into the high MHz region: Pockels and Kerr cells. Pockels cells typically use a solid potassium-deuterium-phosphate (KD*P) crystal to modulate the beam's polarization angle, after which the beam is then passed through a stationary polarizer, amplitude- modulating the light. Kerr cells use a liquid dielectric (often nitrobenzene) to perform a similar action, but require higher voltages.

The polarization angle of some lasers rotates over time. If you are using a gas laser, you can fix the polarization to a constant angle by immersing the laser in a fairly stiff, constant magnetic field.

I used a similar setup in high school to transmit a high-fidelity television signal over a HeNe beam for a distance of two kilometers.

Apart from externally modulating the laser light, as above, semiconductor lasers can be modulated directly.

Thanks You-all, I guess the most practical thing to do is break down and buy a module with analog modulation. I think I can get a Lasever 532nM 100mW for <400usd.

That'd cost less than a AOM

Thanks Again!

Steve

I think I have an old laser modulation until on my shelf from a project that I can donate to you. You will have to search for the specs. From a French company.

I will PM you

Thanks!!!