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FrozenGate by Avery

638nm Divergence question

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blasterman

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I'm planning on upgrading one or two of my light show projectors from 200mW 650s. These were my oldest units, and while at the time they were pretty cool they just can't keep up visually with my newer 445nm and 532nm units. Fairly easy task swapping out diodes.

I'll likely use the Mitsi ML501P73 diodes based on reviews here. My question though is about the divergence of the 638 multimode diodes. Originally I thought this would be an issue, but then I realized I'm only using my red units for flat scanning anyways. From looking at beam shots of the 638s it seems that divergence is only an issue with one axis. If I'm jut flat scanning, I can just rotate the diode so the divergence is on a plane, and then it should be no different than a 650nm...if this makes sense.
 





If you only need one axis to be focused you should be fine. Otherwise, the beam looks more like a bar shining out. The 638nm will look substantially brighter than the 650s, and you can drive them far higher too. Should be good.
 
Just a note I got this going in a Reke-01 (servo) with my single axis, liquid sky hack, and it looks great. Used a big Z-bolt heat sink, and it doesn't even get warm.

Rotated the diode so the wide axis was in the plane of the scanning, and the beam width / divergence is actually tighter than my 445's running G2s and equal to my best greens. Maybe not quite as bright subjectively as a 1watt blue or 100mW green, but certainly keeps ups and is a nice contrast. 200mW 650's might have a bit deeper color, but they just don't have the impact.

Ultimate goal is try try these in a galvo driven scanner, but the beam is pretty wide to fit on those galvo paddles.

I'll shoot some video tonight.
 
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That idea sounds great bro. You say that it isn't as bright as the 445nm or the 532nm so I'm wondering what current it is being run at. Those 500mW Mitsus can pack quite a punch when you power them up to 1.5A.
 
Sure you can drive them that hard but you may be working against yourself if the unit does not have TEC cooling. In a portable host or projector with only passive cooling if you run them @ 1.5A they can shift in wavelength significantly and to me it actually makes them look less bright than running them @ 900mA or under where the diode can maintain a stable wavelength. Plus you loose that unique color as they shift toward 650nm.

These diodes are not what I would be using if I want to burn stuff since they have such poor divergence so I have never seen the need to drive them above 900mA without TEC cooling stabilizing the wavelength.:beer:
 
I'm using the stock 850mA X-Drive and 638 from DTR :) I just use the 12volt circuit inside the projector to power it, and everything is cherry.

I really need these to hit a duty cycle of at least 500hours, so I don't want to push them harder than I have to.

Oh yeah....even though the mitsi diodes are multimode one thing they have over 445's is less of that annoying off axis 'spray'. Not sure what the actual technical term for it is, but even using a pin hole with 445s to try and clean up the off axis glare 638's are just fine by themselves. A big reason I don't drive 445's higher than an amp. Video coming later...I promise
 
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20130216191807.jpg


660 vs 635
 
Here you go - shot this tonight.

From the projector to the back of the monitors is about 60', so the beam is having no problems traversing the smoke. Awesome liquid sky (for a $50 servo based projector), and the video can't do it justice. Might add a few more......but I want to see if the beam will fit on a galvo mirror.

638 diode at 850mA in Reke - 01
 
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Does anyone have a list of mA to mW outputs for the Mitsu diodes? Can't find them anywhere....
 
If/when I end up getting another Mitsu 500 and if time allows I will make an output graph.
 
Hey, so one thing that should help with aligning to galvo mirrors is the fact that the beam on these coming out of the aperture is thicker in the orthogonal direction to the orientation of the final bar.

Since you want the bar aligned with the axis of rotation on your mirror, and in general the mirrors are longer in the axis of rotation the shape of the light from the laser aperture should match up with the mirror as long as you have it fairly close to the mirror! This is going to be the case anyway since once you get past a foot it will have fanned out larger than any galvo mirror I've ever seen.

But yeah hopefully the galvo mirrors you're using are big enough. But even if not, the sheer brightness will outdo anything you can get from 650/660 short of an epic knife-edge setup. The use case of sweeping it along the thin edge of the bar is pretty much perfect for these diodes.
 
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