how do I build a monochrome laser projector

First, you modulate the light intensity of the laser beam.

Second, you need a deflection system of the laser beam. That is necessary because you want to scan a screen with this beam. The screen has to have some remanence (not too much so you don't overlap frames). The principle would be exactly like in a CRT for a TV set. About the deflection system, what I can see is an oscillating mirror. There is another possibility, but I think that it needs a bit of more research, namely, the curbing of the light due to large masses (like a planet).

Guest, just a thought but if you want 256 shades of 'grey' you will need a full spectrum of coloured lasers - at least red, green and blue.

If you are just going to use a single colour laser 532 nm, I think you said, then the monochrome variations will not be grey but different intensities of yellow/ green?

I'm prety sure that when he was talking "gray scale" he meant 256 levels of whatever color he is working with.

Ok jack,

A little more info please... Do you want to send a signal to another device using the laser beam to carry the info OR do you want to project an image (on a wall, for instance) using the laser light?

Let me know.

I would like to take and project a standard vga signal or at least one of the channels on to a wall, I have a 532nm laser; I was thinking of trying to duplicate what an electron beam does in a CRT with mirrors. Scan Horz and Vert lines at 60hz to produce the frame and then maybe use an acoustic modulator to change the size of the dots or adjust the power ouput of the beam to give the illusion of greyscale. Much like a printer halftone dot. I am not clear how convert the video signal to something that is usable.

Most laser light show systems use vector graphics what I am trying to create is a raster system

To answer one of the other comments,why not just buy a projector; becasue it will be an exercise to challange the brain and learn something new.

Thank you for your responses,the links are very helpful. Best Regards Jack

Building your own mechanical scanner. The optics for a 2D scan can get quite interesting, mainly because 60Hz frame, 425 lines, (25500 lines/second) means that you will need to keep the moving parts of the line scanner close to the (small) size that theoretical optical limits allow if it is to stay in mechanically safe regions.

Regarding what you do with the input signal, this depends on the line scanner. If you can find a galvanometer scanner that gives a scan that is uniform enough for your requirements, you can probably use the video systems that were used for the old CRT televisions without significant modification - your only electrical problems will be to convert the level of the luminance signal so it matches the input requirement of your modulator driver, and similarly the scan signal level so that it matches the drive requirements of the galvo driver (be careful if the driver is not integrated with the galvo - overheating can also be a problem).

If you use a prism scanner, in the best case you will also need to generate a method to synchronise the rotation with the scan signal; worst case (if the facets are not parallel) you may need to provide variable delay for the modulator

OK. You can encode the VGA signal for brightness - a circuit that either controls the power on the laser diode or modulate the beam using the VGA signal to trigger an AOM (Acoustic Optical Modulator).

On/Off can be controlled by a TTL signal - many of these small "laser in a box" units have a TTL-IN that can turn the laser on and off.

For the sweep of the beam, I think galvos are going to be your best bet - Check out eBay for all sorts of galvos and dichroic mirrors.

Any help???

I'm probably being dense - but could you explain why you suggest dichroic mirrors?

(N.B. being ancient, I had assumed that 532-nm meant frequency-doubled Nd-YAG - but on reflection (!) you are probably correct that it's a diode laser designed to be used with the same optics)

Jack - can you clarify - is it a diode laser or something much bigger?

Hi, Physicist,

what mean is probably being dense? is it equal to Im interested in it ? or Im vague?

is is an america slang? as well as n.b. being acient?

However, bichronic glass is not same feature as frequcency double crystal has.

one is getting through two color lights butanone si bouble frequency of a light.say from 1064nm to 532nm

All these little 532 nm lasers "in a box" work just about the same...

• A several Watt 808 nm laser diode at one end.
• In front of that, a piece of ND:YVO₄ (yttrium vanadium oxide, doped with neodymium) drops the frequency to 1064 nm (typical YAG λ).
• In front of that, a piece of KTP (KTiOPO₄ - potassium titanyl phosphate) is placed, which gives you the second harmonic of 1064 nm or 532 nm.

A pretty clever way to get 532 nm without having to use the fire power and load of a YAG laser!!! Please see picture...

Thanks.

That raises another question:
Would the TTL modulation in the laser would use a system that comes almost "for free"? If so, would the modulation be via the diode, or would it be via electrical control of the phase-matching in the frequency doubler?
If the former, would the response time of the YVO₄ laser be fast enough?

P.S.1 Given that this would be pre-assembled, I'm still puzzled about the dichroic mirrors...
P.S.2 Is dispersion in the YVO₄ required to compensate dispersion in the KTP? That sounds a bit scary to me - but otherwise I would have expected the right-hand face of the YVO₄ to be transmissive at 1.064u and reflective at 532nm

The TTL is just a two wire input at the back of the power-supply box.

P.S.2 - What are you talking about?

How fast is the TTL input? (My text was intended to say that I expected it to be implemented internally to the laser in the cheapest way possible, and that I was concerned that the more obvious of these could be too slow to be useful for the projector)

PS2: Your diagram shows antireflection coating for 2nd harmonic light on the right-hand side of the YVO₄. The 532nm light that is directed towards the YVO₄ wants to be reflected back so that it enters the KTP with the same phase as thelight that is being generated in the forward path. Because YVO₄ is dispersive, it is usually easier to maintain this phase relationship if the 532nm light does not pass through the YVO₄ - i.e. if it is reflected from the right-hand side of the YVO₄ (or better yet the left-hand side of the KTP - assuming that the coatings can be applied to maintain the appropriate phases). I was just asking if you were aware of the reason why this expected arrangementwas not used.

I don't know if this will help, but let's try (at least the way I interrupt it)...

1. 808nm light comes out of diode and is directed to Nd:YVO4 crystal.
2. The 808nm light passes through the coating on the Nd:YVO4 crystal, where it is converted into 1064nm light.
3. At this point you don't mind if 808nm light escapes, but you want all of the created 1064nm light NOT to escape. You want it to continue out of the Nd:YVO4 crystal on the other side.
4. Notice here that there is a lot of difference between an anti-reflective coating and a "hard-reflective" coating. The Nd:YVO4 crystal in the diagram allows most of the 1064nm light to pass out of the right-hand side of the crystal, but allows NONE of the 1064nm light to pass out of the left-hand side of the crystal - It's "hard reflected" back toward the right.
5. When the beam of 1064nm light reaches the KTP crystal, you want as least as possible of either 1064nm or 532nm light going back to the Nd:YVO4 crystal, hence the anti-reflective coating - note if it was a HR coating all light would have been trapped in the Nd:YVO4 crystal.

Make any sense?

Sorry, but no. Looking at point 5: the AR coating on the right-hand side of the Nd:YVO₄ crystal allows the 532nm light to pass through it and into the Nd:YVO₄, which is both the opposite of what you said and not what I would normally expect.
It also allows the 1.064-um back into the Nd:YVO₄ crystal. Although this is the opposite of what you said, it is exactly what I would expect, for two reasons: first, keeping the frequency doubler inside the lasing cavity means you have a high intensity of 1.064um light, which minimises the length of frequency-doubling medium; and second, having different cavities for the fundamental frequency and for the doubled frequency allows the peaks of any resonances to be coincident.
By the way, in most historical systems the output mirror would be 100% reflective at 1.06um, and still somewhat reflective at 532nm (though naturally less than 100%, so that the optimum amount of 532nm can escape); that would increase the circulating power of the 532nm inside the frequency doubler, thus shortening the length of doubling material that is required. It may be that the non-linearity of KTP and the intensities are such that this is not needed in this particular system - but I think it somewhat unlikely, as historically the only systems where harmonic resonance was not required were high-power pulsed systems.

There are all sorts of hazards. For example, even in a darkened room you will need a relatively powerful laser to project an image of a decent size. Then, high speed rotating scanners have been known to disintegrate, throwing shrapnel in all directions.

Unless you are suitably qualified, I would advise against.

It's nowhere near as bad as you make it sound.

I had assumed this was a build-the-components project. I agree that it becomes relatively safe if Jack uses ready-built components as advised, as the main residual danger would be if he turns the laser on when it is not properly coupled to the scanner (plus, I suppose, more routine electrical issues).

OP why not buy a standard colour laser projector and just feed a monochrome signal into it....

Cheap and simple!!

If you are a beginner first try googling and visiting a few web sites like " www.laserfx.com " to learn some details (visit every nook and cranny of that site).

Try joining photonlexicon.com on line site that specializes in laser enthusiasts both amateur and proffessional.

What you want is monochrome raster scanning which requires a TTL or analog modulatable laser, a laser controller ( Pangolin is good ), a high speed X-Y scanner pair like Cambridge manufacture (good for 60 K PPS " points per second " ).

To get the highest scan speed mechanical galvos like Cambridge can be replaced by acousto optic scanners like those made by NEOS now owned by Gooch & Housego,

They actually have complete systems for video projection that are amazing.

Good luck and play safe.

not bad the link web site.

Hey Jack,

This might be just the thing you're looking for...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200281739057&ssPageName=ADME:B:SS:US:1123