Recent batch of 455nm 500mW laser diodes made available on YKW ...

[LesioQ]

In my 445nm diode setup (simple 405-G-1 lens) I can achieve hardly visible image of single emitters, in a line. When I move around treshold current, I can see the 'firing' order ... i.e. lasing treshold for single emitters. I think I can see 6-7 emitters. The first ones to start tend to occupy the central part of die. When current goes up, all emitters are lasing, making the spot more elongated.

Your picture shows the spot with a weak tail going down. Your setup divergence seems very low. May it be the case that You lost the part of the LD die ? This may be the result of reverse bias ... ?

It would be good if You could go backwards and check the spot pattern without advanced optics, just single lens. This way You could verify all the emitters are 'doing their job'

My diode was very healthy, ca 190mA treshold, high slope. It was slightly better than specified by the seller on his dedicated LD report. I guess You also got Your spec sheet, matching LD box# so You can learn how healthy it was prior to rev. bias.

Piotr.K

[andythemechanic]

Piotr,

it is the same here, I saw not a single line but several spots. If I remember right I have seen 5 so it could be that one or two are gone.
Treshhold of the diode was from spec sheet 180mA and is now 280mA. What I have heard from others was that all diodes performed to spec, so mine got definitely damaged by the reverse bias. Not a big problem though, as long as it will not die very fast now. Power is still a lot for me.

Andreas

[drlava]

It's likely that could be the explanation for the increased lasing threshold. I have seen that damaged single emitter laser diodes have a slightly lower forward voltage than when they were intact, so the damaged emitters could be pulling more than their fair share of current, increasing the apparent threshold of the operating emitters.

[Stoney3K]

It's likely that could be the explanation for the increased lasing threshold. I have seen that damaged single emitter laser diodes have a slightly lower forward voltage than when they were intact, so the damaged emitters could be pulling more than their fair share of current, increasing the apparent threshold of the operating emitters.

I've noticed that behavior with slightly damaged Blurays as well. They keep working, but pulling more current and dropping laser power, generating tons of heat in the process.

Ultimately you end up with a very fancy UV LED.

[FourDee]

I just got mine! No testing yet, I'm awaiting other things first.
They were very nicely packed and I was surprised to see individual test sheets for each diode.

[FourDee]

Sorry for the double post, but I think you guys will get some use out of this.
Based on some experiments Dave did, I made a little calculation of approximate values for different focal lenghts.

The beam width isn't extremely accurate, but I think this may be because it's just hard to measure. I think the divergence is fairly correct though

(FL and beam width in mm, divergence in mrad)

[pullbangdead]

In my 445nm diode setup (simple 405-G-1 lens) I can achieve hardly visible image of single emitters, in a line. When I move around treshold current, I can see the 'firing' order ... i.e. lasing treshold for single emitters. I think I can see 6-7 emitters. The first ones to start tend to occupy the central part of die. When current goes up, all emitters are lasing, making the spot more elongated.

Pics of this happening?

[LesioQ]

Here's an avi. The flashes are from my cellular, not present in laser intensity.
Analog modulation used (0-5V).

Freq is 0.05Hz
Offset is 1.1V
Amplitude is 1.6V

Mobile went through 445nm blocking dichro.

Piotr.K

[drlava]

Are you sure those are separate emitters and not just different modes becoming prominent at different thresholds

[LesioQ]

Definitely not sure. There seems to be some kind of competition between them during slope, but thier positions seem consistent, thus emitters explanation comes to mind.

Piotr.K