Laser questions

[GreekPIC]

So, I had this laser diode from a CD-ROM, with the help of this site:
http://members.misty.com/don/laserdio.htm#diodct2
I was able to find the pinout. I powered it using this schematic:
http://members.misty.com/don/laserdio.htm#diodct3

I pointed the beam to the wall and looked through my NVG. I saw an illuminated circle (dimmer than an IR LED can provide) and it was short of "stripped", illuminated and dark lines.

I read in that page:
For a current below the lasing threshold for your laser diode, there will be some emission due to simple LED action.

I guess that's what happening, I need more current?

 

[audioguru2]

Hi Greek,
There are two powering circuits. The upper one with a regulated current adjustable supply with a 100 ohm current limiting resistor and the lower one with a fixed 10V supply, a 100 ohm current limiting resistor and a 100 ohm pot. Which circuit did you use? ???

If you used the circuit with only a 100 ohm current limiting resistor without an adjustable supply, then you have blown the laser diode since the circuit will feed 85mA to it.

 

[GreekPIC]

I used the first. It's not a disaster if I burnt it, I'm just trying to understand lasers. How can it give light if it's burned? Can the "simple LED action" the guy describe be on if it's burned?

Nikolas

 

[audioguru2]

I used the first. It's not a disaster if I burnt it, I'm just trying to understand lasers. How can it give light if it's burned? Can the "simple LED action" the guy describe be on if it's burned?

One guy said that over-current in a laser diode burns it into an expensive LED in a cool-looking package. ;D

The laser diode has a photodiode in it to sense its output and control the current. You didn't control the current.

 

[GreekPIC]

Ok, thanks. Next time I canibalize a CD-ROM I'll be more carefull...

How yould a circuit that uses the photodiode look like?

 

[audioguru2]

Hi Greek,
I guess a laser brightness regulator would have the laser's photodiode reverse-biased and feeding an opamp. The opamp would compare the output of the photodiode with a reference voltage and drive a transistor or Mosfet to the correct current for the laser.