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2+W single mode by combining 4 LDs (theory)

Light superglue

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During last months I have been playing with Blue-Blue dichro for combining 445 and 462nm checking different types of blue diodes.
Besides multimode LDs I also checked some of highest power single mode ones - among blue and close colours these were of course BDR-209 which according to info found here on LPF should emit at 410-415nm under 600mA, and PLT5 450B emitting at ~447nm under 300mA.

So what I have found is that apart of for combining 445-450nm with 460-465nm, this dichro can very fine work for combining PLT5 450B (92-96% pass) with BDR-209 (80-98% reflection depending on polarisation).

The results for four PLT5 I have tested all with same G-2 lens at 300mA current:
1. 0.23W Pass out of 0.25W before dichro.
2. 0.26W out of 0.27W
3. 0.23W out of 0.24W
4. 0.27-0.28W out of 0.29W

The results for two BDR-209 tested with G-2 at 600mA current:
1. 0.83W Reflection when spot on wall 5 meters away is vertical oval and 0.86W when horisontal oval out of 0.88W.
2. 0.73 and 0.87W out of 0.91W correspondingly.

Regarding these results I would point out that:
-none of my PLT5 turned out to have WL close to 460nm what was dicussed as possible in the thread about this LD. If at least one of four would have, its beam would be reflected instead of passing.
-the Pass/Refl ratio of BDR highly depends on polarisation, what could mean that the 2nd cutoff line on the spectrum curve of this dichro has to be somewhere very close to 415nm - maybe at 425nm or so.
-it seemed that at lower currents (when I adjusted the set up) BDR209 beams were not reflected as well as when overdriven at 600mA, what could mean that the spectrum of this dichro could have a Refl maximum (one of several) somewhere at 410-5nm. It would be interesting if someone could test it with a proper lab spectrometer.

Diachi, do you have one?

Anyway by positioning two BDRs in right polarisations one could combine them with PBS (like janders has done in his Maglite portable) into a beam which would be reflected from dichro with little loss in up to 1.7W residual power and add additional 500mW from a pair of PBSed PLT5. This could result in a 2+W single mode Violet-Blue (VB) beam. Also, DTR wrote me that divergence of these two LD types is similar.

Alienlaser, have you really been able to get 1-1.2W out of single BDR 209? With what driver?
 
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WizardG

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"Alienlaser, have you really been able to get 1-1.2W out of single BDR 209? With what driver?"

And for how long? So far my (limited) experience is that the BDR209 doesn't like extended run times when fed more than 500mA even when water cooled.
 
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1000mW+ out of 405nm BDR-209 ? holy laser beams!!

the only diode i know that could put out power like that is the N!ch!@ diodes... and they cost $600/piece.. or $200-$300 in a tray of 10...
 

CurtisOliver

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It is possible, but this depends on the individual diodes efficiency and it must of been seriously overdriven. The most I got out of mine so far is 847mW @ 520mA (DTR). It is possible that this power output is higher as I didn't leave it to accumulate, but DTR has a max of 950mW @ 520mA on his listing. 1.2W is seriously close to maxing this diode out. We are talking 800mA+.
 

Benm

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Pushing diodes that hard will probably not make them last very long, but the concept of the post gave me an idea:

You could in theory use one diode at a very low temperature (tec controlled) and another identical one at a higher temperature to get a slight difference in wavelength.

The difference would only be a few nanometers, but would it be practially possible to have a dichro selective enough so you could combine these beams realiably?

My experience with dichro's is limited to very different wavelengths (like combining red and green), but i'm not sure what the limitations actually are: how much of a difference in wavelength to you need to be able to make a practical dichro?
 

Light superglue

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Well, even at 500mA the output from BDR-209 should not be much less than at 600mA, so 2W from combination of 2+2 LDs could be possible.

CurtisOliver, what DTR listing do you mean? In his shop he recommends 600mA as maximum current for prolonged life but has test pictures of up to 800mA.

Benm, would not Samsung 5.6mm diodes be better for such testing of the WL shift at TEC cooling? I mean even when in the cold housing the dye in 3.8mm diodes might not have enough copper around for the heat to flow to the housing as fast as in 5.6mm diodes ???
 

Light superglue

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Hi Benm,

I have done this experiment, and in order to avoid hassle with TECs and their drivers I set up the "unique ice-cooled laser" device - the chemist´way of cooling things.
This was made from an old Coca-cola cans car cooler (the Al glass) and three Al 12mm pipe holders from aliexpress (parts for quadcopters) which ones I attached to the plate where TEC was.

The ice+water at 2°C keeps the laser cold all time and at the 596mA current the beam does not pass through the Dichro at all. So the result is negative, it comes out that at cold the BDR-209 beam is reflected by this Dichro completely, so even more than when LD was not cooled!

Such a laser can also be cooled by cans kept in fridge - you do not need to put the laser itself into fridge!
 

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CurtisOliver

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Well, even at 500mA the output from BDR-209 should not be much less than at 600mA, so 2W from combination of 2+2 LDs could be possible.

CurtisOliver, what DTR listing do you mean? In his shop he recommends 600mA as maximum current for prolonged life but has test pictures of up to 800mA.

Benm, would not Samsung 5.6mm diodes be better for such testing of the WL shift at TEC cooling? I mean even when in the cold housing the dye in 3.8mm diodes might not have enough copper around for the heat to flow to the housing as fast as in 5.6mm diodes ???
Sorry Light superglue, I missed this. Alaskan had to point it out.

I believe it was this one I was referring to. 900mW 405nm BDR-209 Blu-Ray Copper Laser Module W/Boost Driver & G-2 Glass Lens

Anyway, it is possible for a BDR-209 to hit over 1W when overdriven.
 
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