[Laser] Laser diode characteristics.

[laser@mailman.qth.net]

Hello group.

After building a couple of simple transmitters based on laser pointers and 
just replacing the mercury cells with a regulated supply of the same voltage, 
I'm now trying a circuit with discrete 650nm diodes. Hopefully this will 
increase power output.

However, in being very cautious, I've noticed that as I slowly increase 
current up to the lasing threshold the device begins to emit laser light but 
after about 30 seconds at that current level, the light output decreases and 
becomes non-coherent again.

Question........Am I seeing an effect which causes the lasing threshold to 
change as the device warms up?     And is this a normal characteristic?

If I switch the device off, wait for two minutes and try again the same thing 
happens, so I haven't killed it.....yet.

Finally, the laser output power appears to increase very rapidly once the 
threshold is reached. Without an optical power meter it's going to be very 
difficult to judge if I'm still within the safe limits. According to the data 
sheet the operating point may be anywhere between 28 and 48mA.  Is there a 
good rule of thumb I can follow e.g. Threshold + 5% is OK but +20% = dead 
laser diode?

I should add that this is with a cheap 5mW diode, but I have a 20mW device 
which I really don't want to destroy by doing something silly.

Thanks

David  G0MRF







--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment. Attachments are not allowed.
Please post in Plain-Text only.---