New Mitsu P73 quad build

[MountainGoat]

Though a shorter wavelength appears brighter, there is one down side: the shorter the wavelength the more orange your beam will be. This would then reduce the overall color gamut of your projector, making it hard (impossible?) to get really deep red colors.

All things being equal (which they rarely are in life), I prefer to balance the brightness of the laser with the color tones being produced.

For example, as an extreme , I believe Planters liquid nitrogen-cooled diode had the wavelength shortened so much that I think he said it was clearly past red and orange , almost approaching a yellow/orange. (Planters, please correct me if i am misspeaking here.). . If you cooled your diode to this extreme, you'd be missing out on some very dramatic reds in your shows.

Questions for Planters:

1) What TECs have you found that work well? Any value in those copper TECs over the Chinese ceramic models?

2) This may be more appropriate for another thread somewhere, but have you any thoughts on a good driver for an array such as this? I'm interest in good color balance and therefore think I need a driver which has excellent modulation characteristics such that I can vary the red intensity over a wide range and develop some nice yellow/ gold tones when combined with green.

I haven't heard too much on this front but honestly haven't looked exhaustively.


Thanks guys.

[jors]

Really interesting post
Mountain, I'm really happy with lasertack drivers w beam suppression
Jors

[planters]

The liquid nitrogen module was built to test these diodes down to extremely low temperatures and to produce a rare 600nm wavelength. The color is orange. There is no yellow in this color. When I run my red diodes down to -30C the color is still very red. Only when you compare this red to a warm diode can you detect a color change and the change is very subtle, but the increase in brightness is stunning. This is why in a real world projector the power of these reds to pull the green to yellow and orange and the blue from violet to magenta overwhelms the slightly decreased red when projecting a pure red beam.

An interesting thing I have found is that when you view a continuous (black body) source through a monochrometer, as you dial the wavelength redder and redder it ceases to look much richer at 650 than at 630. It does change, but not very much. It does grow dimmer, however. Even at 808nm you can see the red if it is bright enough (1/67,000 as bright as the visual peak @555nm) and it looks like a very feeble Mitsu diode. It does not look any redder.

The cooling is a hassle if you are just looking to build a projector, close it up and project shows. But, if you are looking to work with the machine and enjoy engineering the components, then cooling the reds and spatial filtering give a lot of improvement for the effort. I source most of my TECs from:http://www.customthermoelectric.com/tecs_imax.html.

They are not the least expensive route, but each TEC is well characterized and the associated graphs allow you to choose the best combinations based on the available dimensions, power supply voltages and the anticipated cooling load from the running diodes. Buy a few and mess with them; they're a lot of fun.

[MountainGoat]

Lots of good information. Thanks for correcting me and sharing your experience.

[CDBEAM]

WOW !! I Just found this. Where have I been....??? Errr... ah...distracted !!! yea...Beautiful set up Logsquared !!!!!!!!!!! And just a great amount of very interesting info Mr.P !!!!! Thank you.

[MountainGoat]

Well I managed to blow to P73 diode. Maybe it was just a fluke? I had it chilled at about -10C and was only running 1.2amps through it at the time.
I'm hoping it was just an anomaly as I'm not getting as bright of a red as I had hoped. Part of the issue is probably also due to cumulative losses from the cylinderical lenses and spatial filtering.
I have a replacement on order and will post a follow-up on this thread.
The projector is currently running 1.5 watts @ 532nm, ~2-3 watts (with both diodes) at ~635nm, and my blue diodes are in the mail.

[planters]

That is disappointing. The diodes are now LEDs? Do they continue to draw the 1.2 A, but only glow dimly? If you can post an image of the set up it might help to see if there are any characteristics that might have caused this. If you can also list the driver, collimator and other optics that could help as well.

How are you measuring the current input, the optical output and temperature? I am assuming you are running both diodes in series, but even so it is unlikely that both diodes are defective and if they both blew at the same time, then I suspect the set up is causing this and not the diodes themselves. When you mention that cumulative loses may have something to do with this then I am guessing you are measuring the output of the diodes after these components?

Before risking another diode or giving up on the technique I would establish the current output to modulation voltage relationship. Temporarily replace the diode with a 2 ohm resistor (appropriate as a fill in for the P73) and run the driver while measuring the voltage drop across this resistor. This is a closer simulation than running the driver across the current meter of a VOM. Next, measure the optical output of the diode just outside of the module as the current is raised. There is a fairly large range of current near maximum optical output where additional current does not increase output and this is often called the plateau. There is no benefit to running a diode any harder than the lower end of this range and this well below the current where the diode will instantly blow (hundreds of mA).

Beyond this there are other possibilities, but some images of the set up would help.