Revised mirror and dichro layout

[norty303]

Ok, so last year I built a pair of 8W RGB's and they used modules that needed to be well thermally coupled to the baseplate. So this left me with a problem of differing beam heights.
Not a problem, I've done this before, I just use steering mirrors.

However, my original setup (unfortunately I don't think I documented it - I'll grab one tomorrow from the other projector before i take it apart) introduced the green to the red/blue beam between the final steering mirror and galvos.
Seemed like a good idea at the time, but in practise it meant that whenever the red or blue got adjusted very slightly, I had to do a load of work on the green as well.

So I had a bit of a think today and came up with this solution which is much more solid and introduces the green before the steering mirror.
I tested the dichro for transmission and reflect at angles other than 45 degrees and it makes hardly any difference, and starts to actually get better as the angle narrows/widens.

I also took the oppontunity to file grooves out of the base of the mounts laterally and longitudinally so the screw down pressure is focussed on a much smaller surface area. The mounts are much more stable and resistant to moving now when you adjust them.

[jors]

This is a smart idea. thanks. is that steering mirror dielectric broadband laser wave brand?

[norty303]

They may be, I buy those 20x10mm ones from Stanwax and Goldenstar. I also just use the mirrors out of the video projectors. DTR sells the whole optic assemblies which include some really quite excellent dichros.
In particular this narrow band one I used here for the pass red/blue, reflect green.
I find its not worth getting fussy about 1 or 2% on a mirror, with diode based systems you can always just tweak that up a bit anyway, and when you're dealing with multiple watts, the odd 50mW here or there really isn't something you'd notice anyway.

Did the second projector today, much quicker now i knew what i had to do.
Here is what the layout used to be like.

[jors]

Thanks Norty, nice work

[dkumpula]

Thanks for sharing, Norty! Was there a reason for not just raising your green with alum? I just cut plates to size out of scrap stack to the correct height. Although this only saves you one steering mirror, I would think it would be easier to raise your green as opposed to adding an extra mirror on your baseplate. (There is also the minor cost of the extra mirror and mount.)

-David

[norty303]

Raising the green by a very specific amount, whilst maintaining 2 flat surfaces to ensure good thermal interface (the OEM-V-SS heads need the heatsink) was going to require milling capabilities. As I mentiond before, if it was a simple case of tipping the module I'd put washers under one end or the other.
Also, the beam heights of the red/blue modules are never going to be consistent, so the point where the green needs to intersect them is going to vary in height between both projectors (it does). This would mean a lot of to-ing a fro-ing in aligning, measuring, milling, testing, aligning again, etc, etc. And then what if something changes? Mill a new plate, rinse, repeat.

No thanks, I'll stick with an adjustable mount The cost in monetary terms is cheap compared to the time involved in shimming. Besides, £20 for a mount is cheap in terms of a few thousand for a projector, right? The mirrors are essentially free.

[dkumpula]

I hear you. Near-field alignment can be a PITA - even when the modules are starting at the same height.

-David

[drm916]

I hear you. Near-field alignment can be a PITA - even when the modules are starting at the same height.

-David

I agree. I really wish ALL my projectors had a bounce mirror before the dicro. Then I could align everything perfectly. As it stands some of my modules are off my a hair... I have messed with them over and over. Finally gave up on getting them perfect. Maybe now that I have a mill.. I should get back on it and get them perfect height.

[norty303]

The thing is that regardless of what arrangement you use, providing 2 of the modules are relatively close in height, you only need the adjustment on the third beam (I actually have my first bigger RGB projector that has it on 2, but that was before I realised it can be done with just one).

In both of these projectors the red comes out slightly higher, so the perfectly mixed blue/red beam has a slight upwards incline to the steering mirror (hence the big mirror!)

I'm not sure that even with a mill i could get the mix as perfect as it is now. Some of the adjustments are tiny to get the beams perfectly centred in the nearfield on the dichros. That is where the real effort is with alignment. Once you have that sorted, the farfield is a cinch! Lots of haze in the room is a must. I remove the steering mirror so I can stand back at the wall and stare back along a couple of metres of beam (carefully! Even turned down these are multiwatt), through the dichros. Any slight lack of parallel lines really shows up - the human brain seems to be really good at that sort of observation.