Laserdiode

[kinglite]

I guess you mention it because of the heat? The LD is not often at max power and if that is, than it's only for some less seconds.

My collegue guaratie that the LD isn't gliming. He say that it eventually glim at 20mA but never at 1-7mA.
He don't want to show me because it would last one hour to insert this LD into his "construction".

Greets

[ElektroFreak]

Do you have an adjustable lab power supply? If so, turn all current down on a channel and hook the diode up to it. Ramp the current up slowly and see when the diode starts to glow. This will tell you if there is actually an issue with your driver or if the diode just starts to glow at very low current.

[mixedgas]

Do you have an adjustable lab power supply? If so, turn all current down on a channel and hook the diode up to it. Ramp the current up slowly and see when the diode starts to glow. This will tell you if there is actually an issue with your driver or if the diode just starts to glow at very low current.

That assumes a constant current lab supply or a series resistor. Test that supply on a power led like a luxeon first.

In all honestly, I've been working with CW diodes since they were first available commercially and I've never seen one, IR or VIS that did not have some non coherent led like emission around the wavelength its supposed to emit at.

Your eye has a very nice quasi log response, so your seeing a few hundred microwatts of incoherent emission before the diode pops up to lasing threshold. Perfectly normal. Now, if you overdrive them, they very often become weak, non lasing, leds instead of burning out. This occurs when the reflecting faucet is blown off the face of the diode.

Steve

[Psi]

Do you have an adjustable lab power supply? If so, turn all current down on a channel and hook the diode up to it.

I would recommend against this, a typical lab psu isn't spike free.
They can easy kill laser diodes.

Unless of course it's a special psu designed for testing laser diodes or testing spike sensitive electronics.

[ElektroFreak]

In my own experience with my lab supply, as long as you ramp the current up slowly there is no problem. I should have added what Steve said about it needing to be a constant current supply, however. You definitely do not want to just flip a switch and send current to the diode under any circumstances. Slowly applying current is the only way to do it. All paranoia aside, I've never killed a single diode doing this out of the hundreds that I've tested this way..

[kinglite]

Yes I could test it so, but I think I already destroyed one of the LDs :/
and I don't whant to risc to break a second.
I absolutely agree with you that the LD is gliming below Threshold, but my collegue swears on the grave of his mother that it's definitly not gliming beneath the Threshold.
He wants to use my driver for his laser which will be used for shows/projections and that light beneath the threshold would produce a defect in the picture/projection. Is this probably a better type of LD which is better for this sort of application or are all of the LDs emitting that much light beneath the threshold?

Greets

[T0mmm]

I'd say the brightness of the diode when lasing will make the faint,unblanked light almost unnoticeable.

how about putting the LD in an enclosure and collimating it into a beam so you can see how bright it actually is?

[ElektroFreak]

At this point I'd say you can either go with what your colleague tells you or go with what a whole bunch of laser people tell you (some of which are professionals with years of experience). It's your call, but I know what I'd go with.

EVERY diode module I have ever used glows faintly when beneath threshold and they DO NOT cause problems with the imagery displayed. In fact, you don't really want to go too far below threshold with your modulation response since it's much better for the diode that way.

[shrad]

emission below treshold is uncoherent and therefore will not be collimated like a coherent emission, so it will glow some centimeters away of the diode but not in far field