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06-03-2009, 07:25 AM #17
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Quote:
 Originally Posted by chipdouglas thats pretty cool seeing these number for me, because it shows where the LD starts to get more and more efficient. In this case the mw surpasses the ma somewhere between 120-140.
That's not the correct way of thinking about efficiency for laser diodes. The differential, or "slope", efficiency of a laser diode is proportional to the slope of the current vs. power output curve. The differential/slope efficiency is the overall efficiency of the diode. The slope of his chart is basically invariant across the whole range given (R^2 >.999 for a linear fit, so it's a very good line, and doesn't curve visibly), so the efficiency isn't changing. Plot the data, and you can see why there's a point where the mA is equal to the mW with these particular diodes: the slope is greater than 1, but the line is offset because you have to reach a certain current before lasing begins, ie threshold. You can move the "mA = mW" point by changing the efficiency (ie the slope) or changing the threshold current, and either one would change that "mA = mW" point. So, think of efficiency as the slope of the region, and threshold as another important factor in diode operation.

With laser diodes, if anything, the chart gets "less steep" as you increase current, as they get less efficient as you increase current. This is especially evident with CW operation due to heat: if these lasers could survive the optical output, the slope would keep decreasing, and could actually roll over and the slope would become negative, but the diodes die from the optical powers before that happens. With these diodes, you really can't see any change in slope on the ranges given, the optical flux seems to kill them before other effects (eg heat) make the efficiency drop.

06-03-2009, 03:09 PM #18
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Meatball
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haha pullbangdead use calculus much? :P According to your second paragraph, you say that the slope on the graph is increasing at a decreasing rate. This makes sense no doubt, because of the heat. So naturally with an increase in heat, we should also look for an increase in electrical resistance across the diode. Someone ought to plot us a current vs. resistance curve, and according to what physics says about heat and resistance's direct relationship to each other, than we should expect to see a concave up curve on such a graph. With just a bit of Ohm's law, should we not be able to figure that at 350mA, this diode's electrical resistance has been tuned up to 16 ohms? That seems like a lot for a diode....

If my math is correct, (you might all double check me) Then Larry's diode at 350mA, while putting out 441mw of light, should have to dissipate about 1.519 watts of power as heat.. ouch!
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06-04-2009, 01:41 AM #19
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LarryDFW
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Meatball;

The laser diodes are getting to the power levels where heat management is a factor;

1.96 Watts total minus ~0.5 Watt = 1.46 Watts Heat
And this diode has relatively low voltage. This means it is more efficient.

Here is MISTERWILLING's lab heatsink I used while testing the power.

This is a host I designed with better heatsinking, for longer operating times (15-30minutes):

LarryDFW

Last edited by LarryDFW; 06-08-2009 at 10:00 PM.

06-04-2009, 02:10 AM #20
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nikokapo
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Whoa that's a massive heatsink!!

Good to hear the 8x are being tested for longevity

Again, when are these babies going into hosts? We're closer and closer to the James Bond laser :P

06-04-2009, 02:29 AM #21
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Hemlock_Mike
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My 8x pointers don't seem to get too hot even after a minute. My small one is like a roll of nickles.

Mike
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06-04-2009, 02:45 AM #22
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LarryDFW
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Mike;

Keep in mind that the 1st minute is just heating the mass of aluminum.

A few cycles will raise that starting temperature.

I have worked with a lot of Cree UV 3 watt leds which generated about the same 1.5 watts of heat.

They required a fairly large 2" finned heatsink,
to stay at a normal operating temperature, for 10 minutes of operation .

LarryDFW

06-04-2009, 03:18 AM #23
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Hemlock_Mike
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8x is amazing !!
Mike
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06-04-2009, 05:09 AM #24
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LarryDFW
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Bond vs. Laser

Quote:
 Originally Posted by nikokapo Again, when are these babies going into hosts? We're closer and closer to the James Bond laser
Funny you should mention that.

Tonight I was operating the 8X @ 300ma max,
and after immediately popping some thick white balloons @ 30',
I decided to check it out on a fluorescent orange target.

Intensely bright orange, but I noticed it immediately burned thru the target, from about 4' away.

"Strap Mr. Bond down right here on this gold table.
The reflection will get him even before the beam"
.

LarryDFW

Last edited by LarryDFW; 06-04-2009 at 06:09 AM.

06-04-2009, 01:58 PM #25
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Meatball
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I bet that kryton lab style heatsink ought to be sufficient enough for longevity tests etc. Either that, or all these 8X guys better get familiar with TEC components like Jayrob used in the "Ice Box" build of his.

Mike, what's your typical on/off duty cycle?
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06-04-2009, 03:42 PM #26
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Quote:
 Originally Posted by LarryDFW Funny you should mention that. Tonight I was operating the 8X @ 300ma max, and after immediately popping some thick white balloons @ 30', I decided to check it out on a fluorescent orange target. Intensely bright orange, but I noticed it immediately burned thru the target, from about 4' away. "Strap Mr. Bond down right here on this gold table. The reflection will get him even before the beam". LarryDFW

Hahahahaha, awesome!!

06-10-2009, 03:03 AM #27
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LarryDFW
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On another design note...

I finished my new driver circuit for the 8X BR's.

I need to check the current stability,
as the diode heats up to operating temperature.

LarryDFW

06-10-2009, 03:52 AM #28
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Hemlock_Mike
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I lit my Cgar twice last night with my 8x. About 3 seconds.
Mike
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06-10-2009, 04:47 AM #29
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john_lawson
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man this bites my first the PHR 803-t diode came out i was like wow got to get me one of those
so I did and killed it -i was happy after a few builds i got em down
but noo mike and a few others got a hold of this 6x .I was like crudd i need that now
scopeguy helped me get one i killed it ,and thought ok at least it kinda worked ..Glenn gave me a free one -a killer friend--- then Mike and Daguin got this 8x thingy at 500mw
ok i really want that now -but wait rumorts of a 445 nm diode is already here
hows my marriage supposed to last with all these temptations around
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Techlaser 532 100 mw cni pointer 106-110 mw
Wicked laser 532 evo pro 135 mw-mnf sample
Wicked laser spyder pro 2 240 mw mnf sample
Wicked laser spyder 1 pro 180 mw nice sweet unit

kenom kryton groove 405 nm 125 mW phr
enighmus 405 two cr123a host nice 100 mW
6x wicked core 200 mw glass lense

650 loc in susies Rpl host 175 mw glass lense
pen style loc 200 mw glass lense

RPL 532-375 the very first polished host from Jack

Rpl 25 473 polished saweeeet

06-10-2009, 05:13 AM #30
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LarryDFW
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John;

I just obtained one of the new Nichia green 515 nm laser diodes.

http://www.semiconductor-today.com/n...HIA_290509.htm

You have to get one of these new toys just to keep up.

LarryDFW

P.S. I don't really have one .

Last edited by LarryDFW; 06-10-2009 at 05:19 AM.

06-10-2009, 05:23 AM #31
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john_lawson
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Quote:
 Originally Posted by LarryDFW John; I just obtained one of the new Nichia green 515 nm laser diodes. http://www.semiconductor-today.com/n...HIA_290509.htm You have to get one of these new toys just to keep up. LarryDFW P.S. I don't really have one .
dang it larry i read the whol;e article before i saw you were joking lol
__________________
The first step is admitting you have a problem

Techlaser 532 100 mw cni pointer 106-110 mw
Wicked laser 532 evo pro 135 mw-mnf sample
Wicked laser spyder pro 2 240 mw mnf sample
Wicked laser spyder 1 pro 180 mw nice sweet unit

kenom kryton groove 405 nm 125 mW phr
enighmus 405 two cr123a host nice 100 mW
6x wicked core 200 mw glass lense

650 loc in susies Rpl host 175 mw glass lense
pen style loc 200 mw glass lense

RPL 532-375 the very first polished host from Jack

Rpl 25 473 polished saweeeet

06-10-2009, 05:37 AM #32
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scopeguy20
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Quote:
 Originally Posted by john_lawson dang it larry i read the whol;e article before i saw you were joking lol
If I get two of 'em, I'll send one to you JL!
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