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RGB laser projector ver. 2

   Here you will find some info and see some pictures of the second RGB laser projector I built. Unfortunately (or maybe not?), this project is not finished and it never will be, I will explain the reason of that at the end of this text.

   Let's start with some specs:

Red2x 650nm 200mW diode from LPC-815 DVD-RW sled
Green532nm 100mW DPSS module
Blue405nm 115mW diode from PHR-803T HD DVD sled
or 488nm 80mW argon laser
Total output powerabout 500mW
ScannersGSI G100PD closed-loop galvos with GSI amplifier
Dichrosdisassembled from broken computer equipment
DACPopelscan

   The first thing I'm going to show you is the green laser module. It's a Chinese laser module with glued vanadate+KTP crystal and TEC diode cooling. I didn't buy it specially for this projector, I've had it for a pretty long time. It was removed from a broken Shinp SL-7 disco laser which you can see in the first of the following pictures. According to the guy I bought the laser from, the damage was caused by some voltage surge on the DMX line. Most of the electronics inside were destroyed, however the laser module was still working. It turned out that also the TTL input of the laser was not working, but I managed to repair it. The input signal goes directly to CD4066 IC (6x CMOS inverter) and it was simply one of the inverters that was damaged. Fortunately, not all six inverters of this IC were in use so I just had to re-wire the input to an unused one, so not a big deal. You can see the re-wired IC in the third picture.

   After this repair the laser module was working pretty well, I measured it's power in one of labs at the university where I study and the measured power was 120mW (probably including some infrared). You can see that measure in one of pictures above.

   Next is the red laser, I made this module with a view of building a laser projector already. The whole red laser module is made of two 200mW 650nm lasers and a polarization cube beamsplitter (PCBS). Both PCBS and laser diodes comes from DVD writers. The diodes are 'long die open can' laser diodes from LPC-815 laser sleds that are used in LG's 20x DVD writers. For collimators I used something like Aixiz module housings (slightly different version that can be bought here in Poland). The PCBS I used is a bit small for this application, because it is 4x4x4mm when the beam diameter is also 4mm or even a bit more. But I got it from a DVD (that's practically for free) so there's nothing to complain about. In the following pictures and video you can see a quick-and-dirty attempt to combine beams of two lasers, unexpectedly this attempt was successful :D The output power of each laser module was circa 200mW ( @350mA diode current) and after combining I measured 350mW. That's less than 10% power loss on the PCBS, not bad at all! :D

   After success of that experiment I made a simple holder for the PCBS and mounted it together with the lasers on a piece of aluminum heatsink as shown in the following pics. This way I got a 650nm laser with power of about 360mW at 360mA diodes current.

   When I had the green and red lasers ready, it was time to use a dichroic mirror and try making some yellow beam :) As you can see in the following pictures I tried it with the green module I described above but also with another one. The second one has lower maximum power and I don't have a driver for it, so I decided to use that rectangular one in the projector (it was also easier to mount ;) ). This experiment was successful too, the dichro was combining the beams pretty well. I measured that there was 98% transmission @650nm and 93% reflection @532nm.

   When I already knew that the dichro works good, it was time to think about some mounts for it and also about all the mechanics and the optic table.

   First of all, I made something like kinematic mounts for the dichros and mirrors. I made them of an aluminum angle, aluminum sheet, three screws and kind of rubber washers as springs. I needed two mounts for dichroic mirrors (with an aperture in the middle of it, so that one of the light beams could pass through it) and three mounts for turning mirrors (without that aperture). You can see how I made the mounts in the following pics.

   When the mounts has been finished and cleaned, I painted it with black spray so that they look nice ;)

   I used a 3mm thick 35x40cm aluminum plate for the base to mount all this stuff. What had to be placed on it was:
- green laser with it's PSU,
- red laser,
- BluRay laser,
- driver for these two lasers,
- five mirror mounts,
- a pair of galvos in its' holder,
- galvos' amplifier board,
- popelscan DAC board,
- common PSU for the galvos, green and BluRay lasers and popelscan DAC,
- finally, some panel for mounting connectors, switches etc.

As the driver for the red and violet laser diodes I used two-channel current sink that is described HERE at the bottom (the one added on 12th Dec 2009). I designed and made a PCB for that driver specially to use in this projector, however the schematic was designed for driving lasers in my first RGB laser construction which is described HERE.

   In the following three pictures you can see the layout planning process and also the aluminum plate with holes already drilled and threaded.

   Then I started mounting all that stuff on the plate, firstly red and green lasers to make RGY and check if it works at all. As you can see in the following pictures and the video, it does! :D The yellow beam looks pretty nice. In the second of the following pictures you can see that the power is so high that collimated beam (not focused!) sets black paper on fire easily - laser safety precautions has to be taken really seriously!!!

   After that I added the second dichroic mirror and a 405nm laser module. The power of this module was about 110mW - that's poor in comparison to the power of red and green I used, because there should be something like 400-500mW of 405nm to get nice white. But as we say in Poland `if you don't have what you'd like to, you have to like what you got`, or something like that :P In the following pictures you can see the whole projector already working, but there was no PSU for red and violet laser on board yet (I used external PSU).

   And finally some beam pics! :D This is what this laser projector is capable of:

   I wanted to use my 80mW 488nm argon laser for blue color in this laser projector but I met some problems with it. After I bought an EOM (electro-optic modulator) for modulating the laser beam, it turned out that the beam is not polarized :( That means it can not be modulated in any non-mechanical way like with EOM or AOM. I could put a polarizer between the laser and the modulator, but then I would have lost half of the power at the polarizer... But despite that fact I hooked that laser to the projector just to see how the 488nm laser beam will look like in RGB system. You can see this in the following video, there's no blanking on blue color so it's always turned on. In the video I'm stopping the beams with my finger :)

   Then an idea came to my mind and I connected the modulation signal to the current setting input in laser's PSU. In this way I got partial modulation, because when the laser should be off the current was reduced from 10 to 4 amps (the lowest available current with this PSU), what is equivalent to reducing power from 80 to about 15mW. Actually, this power reduce would even be OK for blanking, but this way of modulation is also veeeery slow and probably not safe for both the PSU and the laser.

   Below you can see some pictures with the projector working with the argon laser modulated in the described way. On the pictures the effects looks worse than with 405nm laser, but when watched with naked eye it looks better that violet, especially blue color itself when not mixed with others.


   At that point, when the projector was almost finished (what left to do was some casing and a few other details) I stopped working on it. As I wrote in the beginning, this project has not been finished and will never be. This is because I sold my previous RGB setup, including the galvos and popelscan board that I used in this projector. But as I already had all the lasers and optics laying around, I bought new galvos set (faster and much smaller than the GSI set), made new DAC board and started working on new construction for the projector :D Actually ... it is already finished! `RGB laser projector ver. 2.5` will probably appear on this website soon (at least I hope so) ;)







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