Freak 803T Diode **A New Mystery**

[daguin]

Looks like you really missed the email, huh..

Apparently. Between my classes, my rockhound and mineral lists, and the laser lists, I go through over 200 emails a day. Occasionally, one gets filtered or deleted in error. The first "level" of filtration that I am involved with (there are two automatic levels before this) allows me to delete emails simply based on the subject and sender. Since I don't remember it at all, this is where I probably lost it. You are marked as a "friend" so I would have had to actively check the email for deletion. I was probably aiming for something above or below it in the list and simply "missed."

Thank for catching me back up.

Peace,
dave

 

[IgorT]

And i was already starting to get worried you don't like me anymore..  


I can imagine what answering 200 emails a day looks like, even tho i'm not close to that number, but it can still take hours! And i sometimes read one, decide to answer later, and then forget, because it's not bolded anymore.. It happens..

 

[danq]

And i sometimes read one, decide to answer later, and then forget, because it's not bolded anymore.. It happens..

me too - so I put a "mark as (read/unread)" button on my Thunderbird toolbar, and hit it when I know I want to look at a message again later. There's also a "tag" button for assigning importance, that I use to mark them with a color (red usually) for later handling.

DanQ

 

[Zom-B]

I have a new mystery for you to solve. I have a diode, and while gradually increasing the current and measuring the optical power (to create a graph) I reached 185mA. I was at a stage where I have 5mA steps. The reading was 166.3mW. Next step was 190mA. I saw the reading was 163mW and was gradually dropping. In an instant I realized optical damage was in progress and I have to lower the current NOW. When I did I managed to see a glimpse of 158mW. To see what the damage is, I upped the current again to 180mW and the reading I got was actually higher of the previous measurement at 180mW! (by 3.3mW nonetheless) I slowly increased to 185mW and the reading was again higher than before, ~167mW. I increased the current even more slowly, stopping at every mA, and the laser did not drop in power. When I reached 190mA the reading was 170mW and after a couple of seconds I actually saw the reading increase. I double checked the setup. The laser was not getting too warm. I waited anothe 5 minutes and the laser was emitting above 190mW! It just raised 20+mW at the same current. I did a look at 180mA again to see if it increased globally, and too my surprise it was only 162.7mW, lower than last time but slightly higher than the first time. I went to 190mA again and the output was stable at 180.7mW and did not rise any more. Strange this is. After aimlessly pondering I decided to continue testing with the normal procedure. At 191mW it is 171.2mW, and at 192mA it is 170.1mW. I double-checked this, going back and forth, and it is just that way. Now this is strange again, laser diodes don't just start dropping at a one mA boundary, especially not when a 'knee' has not yet been detected! The laser diode still lives and at 190mA it is still stable.

The whole graph:

The upper part zoomed in, with key points numbered in order they were measured (points in between ignored)

 

[pullbangdead]

The difference between 171.2 and 170.1?  That's .6%.  I don't think there's a meter out there that you can see that small difference and honestly say that there is a statistically significant difference between those 2 numbers.  Those 2 numbers would definitely fall within the error bars of the stated accuracy limits of any meter I've ever seen. *Not trying to nitpick individual numbers within a phenomenon, just exemplifying that it's hard to differentiate numbers when they are so close together.

As for the increase in output power without changing current, I'm not sure about that one.  I still hesitate to say that the laser diode was definitely doing this and there's nothing about the metering set-up that could do make this happen, but maybe it was.  How were you measuring current at the time, as well?  Also, were you measuring voltage across the diode at the time?

 

[Zom-B]

Accuracy limits for meters say that the reading (eg. 171.2mW) differs by, say, 5%, from the actual universal empirical power entering the sensor at that moment. Meters are however much more accurate between their own measurements (relative values). The reading of my meter is stable within two digits, so the reading might have been between 171.0 and 171.4 mW at one time. I can certainly see power differences beyond that, and even sometimes below that.

I was measuring current with a 3% calibrated meter in series with the laser diode and a limiting resistor of 47 ohm/10W (no driver). I was actually measuring the voltage too. However, I have the lab power supply set to constant-voltage, and the current was stable, so unless the resistor changed its value, the diode voltage was stable. I know this very well, as I have to keep adjusting the voltage as the laser warms up between measurements. When going from eg. 100mA to 105mA I have to wait 30 seconds, observing the voltage drop by 0.01V and the current increase by 0.2mA.