[Laser] How do you pulse laser diodes correctly?

[M0AYF]

I have been experimenting with pulse driving some surplus laser diodes from
range finders. I have no data on the diodes so have been "playing it by ear"
so to speak. So far I have pulsed the diodes with currents ranging from
100's of milliamps to several amps and with times ranging from a few 10's of
nS to about 1 microsecond. In all cases I have been able to detect light
being given off by the devices but have been unable to confirm it is laser
light.

I read somewhere that most laser diodes give out polarised light and in the
past have been able to confirm when C.W. IR laser diodes have reached the
lasing threshold by the presence of polarised light. I confirm the polarised
light by rotating a polarised filter in front of the laser diode and then
observe the change in light O/P. With CW diodes I use a CCTV camera/monitor
combination to observe what is happening. With the pulse diodes I have been
using a PIN photodiode (pointing at the laser) connected to an oscilloscope
and then rotating a polarised filter between the laser diode and photodiode
I look for a change in O/P signal from the photodiode. So far I have seen no
change in O/P amplitude and no evidence of laser light.

Is it possible to confirm laser light is being given off by the pulse diode
by this method or some other simple means? Not knowing the device
characteristics is it reasonable to increase the diode pulse current until I
see a definite threshold effect (as in CW diodes) in the light O/P and is
this likely to be the lasing threshold? Any advice or help would be most
welcome.

Regards and 73,s to all in the group.

Des (M0AYF)