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RGB laser

I'm proudly informing that the laser described here took second place in 'The best DIY project of autumn 2009' contest at elektroda.pl portal! :D

   An RGB laser is a kind of laser that emits a single beam of light, but consisting three combined beams: red (R), green (G) and blue (B). These are prime colors and by mixing them in suitable proportions it's possible to get any other color. By simply mixing these three colors (without adjusting the brightness, just turn on or off a component) the following colors can be obtained: red (R), green (G), blue (B), yellow (R+G), magenta (R+B), cyan (B+G), white (R+G+B), and that are possible colors of light emitted by my RGB laser described here.

   There are also other RGB lasers based on a single Ar-Kr gas laser, that works on different spectral lines and emits white light. That white beam goes through switched color filters to obtain different beam colors. However, nowadays RGB lasers are made of three separate lasers and three laser beams are combined to one white beam. Dichroic filters are used for beam combining. Then, to obtain any colour you just need to modulate the power of each laser (R, G and B laser), and that is quite simple in case of diode lasers. This is exactly how my laser is made, below you can see a diagram showing three lasers and beam combining optics.

   The blue laser is a little cheated here because it's 405nm laser diode which is actually rather violet than blue. 405nm laser diodes can be found in BluRay and HD DVD drives, so they're relatively cheap (more about 405nm diodes is in my article HERE). Real blue lasers that emits blue light, which is something around 470nm, are gas or DPSS lasers, and they are very expensive (at least a few hundred dollars). But fortunately there's one nifty trick that can improve the situation with 405nm light! Adding a little of green light to 405nm beam turns it to pretty good blue color. It's just needed to make another power supply for green laser connected parallel with the main green power supply and set to less power. Red laser comes from DVD burner and it's 650nm (description HERE) and green laser is a 50mW laser pointer without it's casing, that's 532nm (description of such pointer HERE). The total optical power is about 50mW max when diodes' currents are set correct to obtain white color. The dichroic filters I used in this project also comes from optical drives. The first one (for combining 532nm with 405nm) is a turning mirror from Xbox360 HD DVD player laser sled. The other one is probably from some DVD or CD drive, I have it in my treasures for a long time and I just don't remember where exactly I have it from. These dichros are not ideal for this purpose because some light is reflected or transmitted when it shouldn't (especially the green light on the first dichro), but they have one really big advantage - they're free ;) )

    Here are some photos. The first one shows my dichro collection harvested over years :) The second and third picture shows the RGB laser setup, first with only the first dichro mounted, and then with both of them.

   Setting the lasers and dichros is not an easy job at all, because the beams must overlap each other perfectly. Normally (when you have some money to spend for the project :) the dichros would be mounted in special adjustable holders, and then all adjustment can be done by rotating tiny screws (which still is not too easy to do). I can't afford such holders so the only way I could get them is to make something similar on my own. But I decided to put all the optics including lasers on an aluminum block and try to adjust it by hand and then glue it to the block. The first thing to do was mount the lasers so that all three beams were in the same plane. Then I put the dichros on the block and began to adjust them by pushing them with a toothpick back and forth on held breath :P That was pretty long and hard job. But somehow in the end I succeeded and then gently glued the dichros to the aluminum block.
   You can see a ready-to-work setup on three pictures below.

   I didn't have a 3-channel laser didoe driver to power this laser, so at first I run it by three different current sources that I had from experiments with lasers I've made before. The following picture is made of seven separate photos and it shows the laser spot with all available colors. It works!!! :D

   I reached this point at the end of June and then the work stopped because of summer holidays (you know, all that trips, parties, laying on the beach - who would stay at home and pore over a laser :P ). I pushed this project further a few days ago (in late September), when I got a flu so I had to sit at home anyway. So next things to do was some casing for all that optics and a laser diodes driver. By the way, this article is probably the one that appeared here on the website the fastest, because it's the next day after I finished building it! :D

   Here are some photos showing the laser in a new beautiful wooden-aluminum casing ...

   ... and a 3-channel adjustable constant current sink as the laser diodes power supply.

   The laser diodes PSU is made only from nine transistors (three per channel), ref. voltage source and some resistors. Current adjustment is a must here because it's necessary to set correct ratio between laser powers to obtain white color. You can download the schematic of the driver from here:

  • RGB_DRV.pdf

       I'm sure many people will wonder why I used so strange transistors in this circuit. I'm a guy who don't like to go to electronics shop and spend money if he don't have to, so I just used components recycled from old electronic equipment. Almost ANY NPN transistors and ANY N-MOSFETs of similar size could be used here.

       After making a casing and a PSU for the laser I considered the project finished. So it was the highest time to see some cool effects :) Directing a white laser beam at a diffraction grating was pretty good for the beginning. The diffraction grating splits different wavelengths with different density, so it splits white light beam to many red, green and blue beams. I took this diffraction grating out of a DVD writer (looks like such thing can't be found in any drive, unfortunately), but a CD disk would work here pretty good too. The data paths on the CD are so close to each other that they acts like a diffraction grating (and that's why the CD disks makes rainbow patterns when you put it under light).
       Below some pictures showing the laser directed at a diffraction grating.

       After a short play with a grating I had to take out my galvo scanners and hook it up to the laser. Below a few pictures of the RGB laser and galvos cooperation.

       I used Popelscan 3.1 software for controlling the galvos as usual, but I had to make some upgrade in the DAC board. There was only one laser blanking output and I needed three for R, G and B components. Fortunately the software can control RGB laser, I just needed to hook up an additional latch to the board (three D flip-flops were needed, I used 74ls273 IC). Firstly I planned to make a new PCB for the interface, but I'm so lazy that I decided to just add the IC to the PCB I have :P
       You can download a complete schematic of this interface here:

  • Popelscan_RGB.pdf

       I think the schematic doesn't need much explanation. Potentiometers are for adjusting gain and offset of both X and Y analog signals. Besides three blanking outputs: R, G and B, there's also one named tot. blank. (total blanking) - this is simply a sum of R, G and B blanking signals that can be used for blanking one laser if you don't have RGB yet ;)
       Below a picture of modified DAC board and in the right picture all setup with description.

                     

       Simple graphics, like a rainbow line or circles can be easily 'painted' in the Popelscan software itself. But there's no easy way to put some text or more complicated graphics into the projection. That's why I wrote a program for conversion BMP files to Popelscan's MOT files :) I mentioned this program before in my argon laser description, but I had to modify it a bit for support of different colors.
       Here's a screenshot of the program's window and below it a link for download.

  • bmp2mot.exe (330kB)

       Well, looks like that's all I have to say. Below you can see some pics of my RGB laser at work - pretty nice effects! To increase beams visibility I made some smoke with soldering iron and rosin :P There's also a short video at the bottom. Almost nothing can be seen on the vid but since I made it I decided to put it here anyway ;)

    [ ADDED ON 6.03.2009 ]

       Somebody asked me if I would like to sell the projector from the pictures that you can see above. I put it together on a piece of wood and sold it :) In the pictures at the bottom you can see the final version of tis projector.






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