Ith and 445nm Diodes ??

[LazyBeam]

I've read the Ith for these diodes (A130 & A140) is ~200-220mA with ~30mW of output.

How does temperature affect Ith in practice?
Is there a big jump in Ith or does the output just drop as the temperature rises?

 

[JLSE]

Threshold can be from 180mA-210mA on average. The colder the ambient temp, the lower the threshold. I have had mine run as low as 5mw, but this will not last unless the temp can be controlled. With 200mA in, they heat up fairly quick. The output drops, and the threshold increases.

The 445 LD's are temperature dependent unlike anything seen in common 650 or 405nm diodes.

 

[LazyBeam]

What's a reasonable setting for mA if I want to set a 445nm diode as low as it will go without Ith fluctuating under the set mA? I just want as low of a power as possible but with some margin for realiable operation as it heats up.

Edit: Ideally, I'd love to be <40mW... the lower the better.

 

[daguin]

What's a reasonable setting for mA if I want to set a 445nm diode as low as it will go without Ith fluctuating under the set mA? I just want as low of a power as possible but with some margin for realiable operation as it heats up.

Edit: Ideally, I'd love to be <40mW... the lower the better.

This would be an experiment you need to do. When getting to the "edges" of output, the diode-to-diode variability will become a factor. Does your particular diode lase at 180mA or at 220mA? That individual lth will affect the current needed to work the way you want it to.

At 1000mA, +-20mA doesn't make much difference. At 200mA +-20mA does make a difference, especially when skirting the boundary of lasing.

Peace,
dave

 

[JLSE]

What's a reasonable setting for mA if I want to set a 445nm diode as low as it will go without Ith fluctuating under the set mA? I just want as low of a power as possible but with some margin for realiable operation as it heats up.

Edit: Ideally, I'd love to be <40mW... the lower the better.

That is something you may want to experiment with. Each LD is going to have its own characteristics to an extent. But your main concern is going to be controlling the temp.

In a pen build, you are going to have behavior like that seen in a DPSS. The moment it warms up, the output is going to fall. Im not sure which is more drastic, but you get the idea...

In a larger hand held, you can get the lower mW, but again when the temp begins to rise, the output will begin to drop. Stability will depend more or less on the heat-sinking and dissipation abilities..

I have an order that has to go out tonight, I will run a couple of tests at ~40mW and see what happens while I have it on the bench.

 

[LazyBeam]

I don't much care about power stability at lower powers as long as it's between 5mW and 40mW and keeps lasing.
I'd like to use it for a pointing application without worrying about hurting people's eyes with diffuse reflections.

 

[JLSE]

So I tested a random 445 with no additional heat sinking other than the rear cap of an aixiz module and the metal lens holder with an aixiz 405nm AR...

At 5mW the output lasts less than 10 seconds before dropping out. This could be extended, but its extremely touchy with the slightest heat.

At 40mW, the laser ran for 3mins @ 234mA, steadily dropping its output... see graph.

You could maintain a low output, but if its for a pen, only short bursts of use will work. The heat from your hand alone will also affect where the threshold sits, and may want to factor this in when making your setup. You would have to keep the laser in your pocket or warm prior to use to ensure the output does not exceed your 'safe mW' as would happen when cold...